Neurosurgery

01 Neuroanatomy — Cranial, Ventricular, & Vascular

A thorough understanding of cranial anatomy is the foundation of neurosurgical practice. The skull base, cerebral vasculature, and ventricular system define the corridors and constraints of every neurosurgical approach.

Cranial Fossae

The interior of the skull base is divided into three fossae. The anterior cranial fossa is formed by the orbital plates of the frontal bone, cribriform plate of the ethmoid, and lesser wing of the sphenoid; it houses the frontal lobes and olfactory bulbs. The cribriform plate is the thinnest portion of the skull base — fractures here cause CSF rhinorrhea and anosmia. The middle cranial fossa is formed by the greater wing of the sphenoid and temporal bone; it contains the temporal lobes, pituitary fossa (sella turcica), and the cavernous sinus. Key foramina: foramen rotundum (V2), foramen ovale (V3, accessory meningeal artery), foramen spinosum (middle meningeal artery — epidural hematoma source), and the superior orbital fissure (CN III, IV, V1, VI, ophthalmic veins). The posterior cranial fossa is formed by the occipital bone and petrous temporal bones; it contains the cerebellum, brainstem, and CN IV–XII. The foramen magnum transmits the medulla oblongata, vertebral arteries, and spinal accessory nerves (CN XI ascending roots).

Cerebral Lobes & Functional Areas

The frontal lobe (anterior to the central sulcus) contains the primary motor cortex (precentral gyrus), Broca's area (dominant inferior frontal gyrus — expressive speech), supplementary motor area, and frontal eye fields. The parietal lobe contains the primary sensory cortex (postcentral gyrus) and association areas for spatial awareness; lesions of the non-dominant parietal lobe cause hemispatial neglect. The temporal lobe houses the primary auditory cortex (Heschl's gyrus), Wernicke's area (dominant posterior superior temporal gyrus — receptive speech), hippocampus (memory), and amygdala. The occipital lobe contains the primary visual cortex along the calcarine fissure. The insula, deep to the Sylvian fissure, is involved in pain processing, autonomic regulation, and taste.

Ventricular System

CSF is produced primarily by the choroid plexus (~500 mL/day; total CSF volume ~150 mL, turnover 3–4 times daily). Flow pathway: lateral ventricles → foramen of Monro (interventricular foramen) → third ventricle → cerebral aqueduct (of Sylvius) → fourth ventricle → exits via the foramina of Luschka (lateral, paired) and foramen of Magendie (midline, posterior) → subarachnoid space → absorbed at the arachnoid granulations into the superior sagittal sinus. Obstruction at any point in this pathway produces obstructive (non-communicating) hydrocephalus. The cerebral aqueduct is the narrowest point and the most common site of obstruction (aqueductal stenosis, tectal plate glioma, pineal region tumor).

Arterial Supply — Circle of Willis

The brain receives ~15% of cardiac output via two paired arterial systems. The internal carotid arteries (ICA) enter the skull through the carotid canals, traverse the cavernous sinus, and give off: ophthalmic artery (first intradural branch), posterior communicating artery (PComm), anterior choroidal artery, then bifurcate into the anterior cerebral artery (ACA) and middle cerebral artery (MCA). The vertebral arteries enter through the foramen magnum, give off the posterior inferior cerebellar arteries (PICA), then unite to form the basilar artery, which gives off the anterior inferior cerebellar arteries (AICA) and superior cerebellar arteries (SCA) before bifurcating into the posterior cerebral arteries (PCA).

The Circle of Willis connects these systems: ACA — anterior communicating artery (AComm) — contralateral ACA; ICA — PComm — PCA. A complete Circle of Willis is present in only ~25% of the population. The AComm is the most common site of intracranial aneurysms (~30%), followed by the PComm (~25%) and the MCA bifurcation (~20%).

Venous Sinuses

The dural venous sinuses are valveless channels between the periosteal and meningeal layers of dura. The superior sagittal sinus (SSS) runs in the superior margin of the falx cerebri from the crista galli to the confluence of sinuses (torcular Herophili). Parasagittal bridging veins drain cortical surface blood into the SSS — these are stretched and torn in acute subdural hematomas. The transverse sinuses run laterally from the torcular along the tentorium to become the sigmoid sinuses, which exit through the jugular foramina. The cavernous sinus surrounds the sella turcica and contains the ICA and CN VI traversing through its center, with CN III, IV, V1, and V2 in its lateral wall. Cavernous sinus thrombosis presents with proptosis, chemosis, ophthalmoplegia, and facial sensory loss.

Cerebral Arterial Territories & Stroke Syndromes

Meninges

Three membranes envelop the brain and spinal cord. The dura mater is the outermost, toughest layer; in the cranium it has two layers (periosteal and meningeal) that separate to form the dural venous sinuses. Dural folds compartmentalize the intracranial space: the falx cerebri (separates cerebral hemispheres; contains the SSS superiorly and inferior sagittal sinus inferiorly) and the tentorium cerebelli (separates the cerebral hemispheres from the cerebellum; the tentorial notch transmits the midbrain and is the site of transtentorial/uncal herniation). The arachnoid mater is a delicate, avascular membrane beneath the dura; the subdural space is a potential space between the dura and arachnoid (where subdural hematomas collect). The pia mater is intimately adherent to the brain surface, following every gyrus and sulcus; the subarachnoid space (between arachnoid and pia) contains CSF and the major cerebral arteries.

02 Neuroanatomy — Spinal Cord & Peripheral Nerves

Spinal Cord Anatomy

The spinal cord extends from the foramen magnum to approximately the L1–L2 vertebral level in adults (the conus medullaris). Below this, the lumbar and sacral nerve roots form the cauda equina. The cord has two enlargements: the cervical enlargement (C4–T1, brachial plexus) and the lumbar enlargement (L1–S3, lumbosacral plexus). The filum terminale is a pial strand anchoring the conus to the coccyx.

In cross-section, the cord has an H-shaped central gray matter surrounded by white matter tracts. Key tracts: the corticospinal (pyramidal) tract — descends in the lateral white matter (lateral corticospinal tract, crossed at medullary pyramids); lesions cause ipsilateral upper motor neuron weakness. The dorsal columns (fasciculus gracilis — lower extremities, medial; fasciculus cuneatus — upper extremities, lateral) carry proprioception, vibration, and fine touch; they are ipsilateral and cross in the medulla. The spinothalamic tract carries pain and temperature; fibers cross within 1–2 levels of entry and ascend contralaterally.

Spinal Cord Syndromes

Nerve Root Localization

03 The Neurosurgical Physical Exam

Glasgow Coma Scale (GCS)

The GCS is the most widely used scale for assessing level of consciousness in neurosurgical patients. Score ranges from 3 (worst) to 15 (best). It is composed of three components:

Pupillary Examination

Assess size, symmetry, and reactivity. Unilateral fixed, dilated pupil (mydriasis): ipsilateral CN III compression — most commonly from uncal herniation pushing the temporal lobe through the tentorial notch, compressing CN III against the posterior clinoid. This is a neurosurgical emergency requiring immediate intervention to relieve the herniation. Bilateral fixed, dilated pupils: bilateral CN III compression from severe raised ICP or brainstem death — very poor prognosis. Bilateral pinpoint pupils: pontine lesion (hemorrhage or ischemia), opioid toxicity. Horner syndrome (miosis, ptosis, anhidrosis): disruption of the sympathetic chain — central (brainstem/spinal cord lesion), preganglionic (Pancoast tumor, carotid dissection), or postganglionic (cavernous sinus lesion).

Cranial Nerve Examination

CN I (olfactory): test each nostril separately with coffee, peppermint; anosmia occurs with cribriform plate fractures or olfactory groove meningiomas. CN II (optic): visual acuity, visual fields (confrontation), fundoscopy (papilledema = raised ICP), relative afferent pupillary defect (RAPD, Marcus Gunn pupil — swinging flashlight test). CN III, IV, VI: extraocular movements; CN III palsy = "down and out" eye, ptosis, mydriasis; CN IV palsy = hypertropia worsened with contralateral head tilt (Bielschowsky test); CN VI palsy = inability to abduct (often a false localizing sign of raised ICP). CN V: facial sensation in V1/V2/V3 distributions, masseter/temporalis strength, corneal reflex (afferent V1, efferent VII). CN VII: facial symmetry at rest and with movement; UMN lesion = contralateral lower face weakness (forehead spared); LMN lesion = ipsilateral entire hemiface weakness. CN VIII: hearing (finger rub, Rinne/Weber), vestibular function. CN IX/X: gag reflex, palate elevation (uvula deviates away from lesion), hoarseness. CN XI: sternocleidomastoid (turns head to opposite side), trapezius (shoulder shrug). CN XII: tongue protrusion (deviates toward the side of the lesion in LMN injury).

Motor Examination

Assess strength using the MRC (Medical Research Council) scale: 0 = no contraction; 1 = flicker; 2 = movement with gravity eliminated; 3 = movement against gravity; 4 = movement against resistance (4−, 4, 4+); 5 = normal. Assess tone (spasticity vs rigidity vs flaccidity), pronator drift (subtle corticospinal tract dysfunction), and deep tendon reflexes. Pathologic reflexes: Babinski sign (upgoing toe with plantar stimulation = UMN lesion); Hoffman sign (flicking the middle finger distal phalanx produces involuntary flexion of the thumb and index finger = cervical myelopathy).

Cerebellar Examination

The cerebellum coordinates movement, balance, and muscle tone. Test for: dysmetria (finger-nose-finger, heel-knee-shin — past-pointing), dysdiadochokinesia (rapid alternating movements), intention tremor (worsens approaching the target), ataxic gait (wide-based, unsteady), nystagmus (fast component toward the lesion side), and Romberg sign (proprioceptive, not cerebellar — patient falls with eyes closed if dorsal column deficit). Cerebellar lesions produce ipsilateral deficits.

Herniation Syndromes

04 Neurosurgical Principles — ICP, CPP, & Brain Relaxation

Intracranial Pressure (ICP)

Normal ICP in adults is 5–15 mmHg (supine). The Monro-Kellie doctrine states that the cranial vault is a fixed volume; the sum of brain parenchyma (~80%), blood (~10%), and CSF (~10%) must remain constant. An increase in any one component must be offset by a decrease in another, or ICP will rise. Initially, CSF is displaced into the spinal subarachnoid space and venous blood is compressed out of the sinuses (compensatory mechanisms). Once compensation is exhausted, small additional volume increases cause dramatic ICP elevations (steep portion of the intracranial compliance curve).

ICP Monitoring

Indications (BTF guidelines): severe TBI (GCS ≤8) with an abnormal CT, or with a normal CT if two or more of the following are present: age >40, unilateral or bilateral motor posturing, or systolic BP <90 mmHg. Types of monitors: External ventricular drain (EVD) — gold standard; catheter placed in the lateral ventricle (usually right, at Kocher's point: 11 cm posterior to the nasion, 3 cm lateral to midline, aimed at the medial canthus of the ipsilateral eye in the coronal plane and toward the tragus in the sagittal plane); allows both measurement and therapeutic CSF drainage. Intraparenchymal monitor (Camino, Codman) — placed in the brain parenchyma; cannot drain CSF but less infection risk and easier to place.

Cerebral Perfusion Pressure (CPP)

CPP = MAP − ICP. Target CPP: 60–70 mmHg (BTF guidelines recommend maintaining CPP ≥60 mmHg; aggressive attempts to keep CPP >70 mmHg are associated with ARDS and should be avoided). Cerebral autoregulation normally maintains constant cerebral blood flow (CBF) across MAP 50–150 mmHg; this autoregulation is often impaired after TBI, making CBF directly dependent on CPP.

ICP Management — Tiered Approach

Brain Relaxation During Surgery

Techniques to achieve a "slack" brain during craniotomy: mannitol or hypertonic saline (given 30 min before dural opening); CSF drainage (lumbar drain placed preoperatively, or EVD, or opening the Sylvian cisterns to release CSF); mild hyperventilation (PaCO₂ 30–35 mmHg during the approach, return to normocarbia once the lesion is accessed); head elevation (promotes venous drainage); avoid jugular venous obstruction (head position, tape securing ETT); and appropriate anesthetic depth (avoid coughing, straining). If the brain remains "tight" despite these measures, consider the possibility of an evolving contralateral lesion (obtain intraoperative imaging or inspect the contralateral side).

Cerebral Blood Flow Physiology

Normal CBF is ~50 mL/100 g/min. Ischemic threshold: CBF <20 mL/100 g/min → neuronal dysfunction (reversible); CBF <10 mL/100 g/min → infarction (irreversible). Factors affecting CBF:

05 Gliomas — WHO Classification & Management

Gliomas are the most common primary malignant brain tumors in adults, arising from glial cells (astrocytes, oligodendrocytes, ependymal cells). The 2021 WHO Classification of CNS tumors integrates molecular markers — particularly IDH mutation status and 1p/19q co-deletion — into diagnosis and grading.

WHO Classification (2021)

Glioblastoma (GBM)

The most common and most aggressive primary brain tumor. Incidence peaks at age 55–85. Presents with headache, seizures, progressive focal neurologic deficit, or personality changes. MRI shows an irregularly enhancing mass with central necrosis and surrounding vasogenic edema (T2/FLAIR hyperintensity). Standard treatment (Stupp protocol): maximal safe resection → concurrent temozolomide (TMZ) + radiation (60 Gy in 30 fractions) → adjuvant TMZ for 6 cycles (Stupp et al., 2005; PMID: 15758009). MGMT promoter methylation predicts TMZ responsiveness (median survival ~21 months with methylation vs ~14 months without).

Low-Grade Gliomas (WHO Grade 2)

Present in younger patients (30–40s), often with seizures. MRI shows a non-enhancing, T2/FLAIR hyperintense lesion without necrosis. IDH-mutant astrocytomas and oligodendrogliomas have significantly better prognoses than IDH-wildtype tumors. Management: maximal safe resection (extent of resection correlates with OS); observation vs early adjuvant therapy based on risk factors. High-risk features (age >40, subtotal resection, tumor >6 cm, tumor crossing midline, non-oligodendroglioma histology, neurologic deficit) favor early radiation + chemotherapy (PCV for oligodendrogliomas — RTOG 9802, PMID: 27050206; TMZ also used).

Ependymoma

Arises from ependymal cells lining the ventricles. In children, most are posterior fossa (fourth ventricle); in adults, most are spinal (intradural intramedullary). WHO grade 2 or 3. The RELA fusion-positive variant (supratentorial) carries a worse prognosis. Treatment: gross total resection is the primary goal; adjuvant radiation for subtotal resection or anaplastic histology. Chemotherapy has limited efficacy in ependymomas.

Extent of Resection in Glioma Surgery

Molecular Markers in Glioma — Clinical Relevance

06 Meningiomas

Meningiomas are the most common primary intracranial tumors overall (~37% of all CNS tumors), arising from arachnoid cap cells. Most are benign (WHO grade 1, ~80%), slow-growing, and affect women more than men (2:1). They express progesterone receptors (may grow during pregnancy). Risk factors include prior cranial irradiation, NF2 (multiple meningiomas), and female sex.

Common Locations & Presentations

Simpson Grading of Meningioma Resection

WHO Grading

Grade 1 (benign): ~80% of meningiomas; typical histologic subtypes (meningothelial, fibrous, transitional, psammomatous); slow growth; surgery alone is usually curative. Grade 2 (atypical): ~15–20%; defined by increased mitotic activity (4–19 mitoses per 10 HPF), brain invasion, or 3+ of 5 features (sheeting architecture, prominent nucleoli, high cellularity, small cell change, necrosis); higher recurrence rate; consider adjuvant radiation after subtotal resection. Grade 3 (anaplastic/malignant): ~1–3%; ≥20 mitoses per 10 HPF, or frank anaplasia; aggressive behavior with brain invasion and potential metastasis; adjuvant radiation recommended regardless of resection extent.

07 Pituitary Tumors

Pituitary adenomas account for ~15% of intracranial tumors. They are classified by size (microadenoma <10 mm vs macroadenoma ≥10 mm) and by hormonal activity (functioning vs non-functioning).

Functioning Adenomas

Non-Functioning Adenomas

Comprise ~30–40% of pituitary tumors. Typically present as macroadenomas with mass effect: bitemporal hemianopsia (compression of the optic chiasm from below — superior temporal fibers are compressed first), headache, and hypopituitarism (compression of the normal gland — typically GH lost first, then LH/FSH, TSH, ACTH, and prolactin last). Elevated prolactin may occur due to stalk effect (compression of the infundibulum preventing dopamine from reaching the anterior pituitary, causing mild prolactin elevation, typically <100 ng/mL — in contrast, prolactinomas cause prolactin levels proportional to tumor size: macroadenoma prolactinomas usually >200 ng/mL).

Transsphenoidal Surgery

The endoscopic endonasal transsphenoidal approach is the standard surgical technique for pituitary tumors. The approach traverses the nasal cavity → sphenoid ostium → sphenoid sinus → sellar floor (bone is thinned or removed) → dura is opened → tumor is removed. Key anatomic landmarks: the sphenoid septum (may be deflected), carotid prominences (lateral walls of the sphenoid sinus — must be identified to avoid ICA injury), opticocarotid recesses, and the sellar floor. Reconstruction of the sellar defect after tumor removal uses abdominal fat graft, fascia lata or synthetic dural substitute, and a nasoseptal flap (Hadad-Bassagasteguy flap) to prevent CSF leak.

08 Metastatic Brain Tumors

Brain metastases are the most common intracranial tumors overall, outnumbering primary brain tumors ~10:1. The most common primary sources are lung (~40–50%), breast (~15–25%), melanoma (~5–20%), renal cell carcinoma, and colorectal cancer. Metastases tend to occur at the gray-white matter junction (hematogenous spread via end-arteries). Distribution follows blood flow: ~80% cerebral hemispheres, ~15% cerebellum, ~5% brainstem.

Management

Treatment decisions depend on number and size of metastases, performance status, controlled vs uncontrolled systemic disease, and histology. Options include:

Surgical resection: indicated for single, accessible metastasis with good performance status and controlled systemic disease; also for tissue diagnosis when unknown primary, and for large symptomatic lesions causing mass effect. The landmark Patchell trial demonstrated that surgery + WBRT was superior to WBRT alone for single brain metastases (Patchell 1990, PMID: 2405271).

Stereotactic radiosurgery (SRS): single high-dose focused radiation (Gamma Knife, CyberKnife, LINAC-based); effective for 1–4 metastases, each ≤3 cm; increasingly used for more lesions. Local control rates ~80–90%. SRS to the resection cavity after surgery reduces local recurrence.

Whole brain radiation therapy (WBRT): 30 Gy in 10 fractions; used for multiple metastases (>4), leptomeningeal disease, or poor performance status. Associated with cognitive decline. Hippocampal avoidance WBRT + memantine can mitigate cognitive toxicity (NRG CC001, PMID: 31454575).

09 Posterior Fossa Tumors

Vestibular Schwannoma (Acoustic Neuroma)

Benign tumor arising from Schwann cells of the vestibular portion of CN VIII, typically at the internal auditory canal (IAC). Presents with unilateral sensorineural hearing loss (most common symptom, insidious onset), tinnitus, and disequilibrium. Large tumors compress CN V (facial numbness) and CN VII, and may cause brainstem compression and hydrocephalus. Bilateral vestibular schwannomas are pathognomonic for NF2. MRI shows a enhancing CPA mass with extension into the IAC ("ice cream cone" appearance).

Management options: observation (small, asymptomatic, elderly patients — serial MRI); stereotactic radiosurgery (tumors ≤3 cm, tumor control ~95%); microsurgical resection via retrosigmoid, translabyrinthine (sacrifices hearing), or middle fossa approach (preserves hearing for small tumors). The goal is tumor control with preservation of facial nerve function (House-Brackmann grade I–II).

Medulloblastoma

The most common malignant brain tumor in children (~20% of pediatric brain tumors). Arises in the posterior fossa — from the cerebellar vermis in children (midline), from the cerebellar hemispheres in adults. WHO grade 4 embryonal tumor. Molecular subgroups (2021 WHO): WNT-activated (best prognosis, ~90% OS), SHH-activated (TP53-wildtype vs TP53-mutant), Group 3 (worst prognosis, often MYC-amplified), and Group 4 (most common). Presents with signs of obstructive hydrocephalus (headache, vomiting, ataxia, papilledema) and cerebellar signs. Can disseminate via CSF (drop metastases to the spine). Treatment: maximal safe resection → craniospinal irradiation (CSI) + boost → adjuvant chemotherapy (vincristine, cisplatin, cyclophosphamide).

Hemangioblastoma

Benign (WHO grade 1), highly vascular tumor, most commonly in the cerebellar hemispheres (posterior fossa). ~25% are associated with von Hippel-Lindau (VHL) syndrome (autosomal dominant; also associated with retinal hemangioblastomas, clear-cell renal cell carcinoma, pheochromocytoma, and pancreatic cysts/neuroendocrine tumors). MRI characteristically shows a cystic lesion with an enhancing mural nodule. The nodule is the tumor — the cyst wall is non-neoplastic (only the nodule needs to be resected). Key surgical principle: these are hypervascular; preoperative angiography and embolization may be considered for large tumors. Associated with polycythemia (tumor secretes erythropoietin).

Craniopharyngioma

A benign (WHO grade 1) but locally aggressive epithelial tumor arising from Rathke's pouch remnants in the sellar/suprasellar region. Bimodal age distribution: children (5–15 years) and adults (45–65 years). Two histologic subtypes: adamantinomatous (more common in children; calcifications, cystic with "machinery oil" fluid; CTNNB1/beta-catenin mutations) and papillary (almost exclusively in adults; rarely calcified; BRAF V600E mutations — amenable to targeted therapy). Presents with visual loss (optic chiasm compression), endocrinopathy (panhypopituitarism, growth failure in children, diabetes insipidus), and headache. Surgery (transsphenoidal or transcranial) aims for gross total resection but must be balanced against hypothalamic injury risk (hypothalamic obesity, severe memory and behavioral deficits are devastating — subtotal resection + radiation may be preferred when hypothalamic involvement is significant). Recurrence rate after GTR: ~10–20%; after STR without radiation: ~50–70%.

Primary CNS Lymphoma (PCNSL)

Diffuse large B-cell lymphoma arising within the CNS, without systemic involvement at diagnosis. Increased incidence in immunocompromised patients (HIV/AIDS, transplant recipients) but also occurs in immunocompetent patients (median age 60). MRI: typically deep-seated (periventricular), homogeneously enhancing (in immunocompetent), may be multifocal. Key principle: suspected PCNSL should NOT be resected — surgical role is limited to biopsy for tissue diagnosis. Hold steroids before biopsy if possible (steroids cause rapid tumor lysis and may render biopsy non-diagnostic — the "vanishing tumor"). Treatment: high-dose methotrexate-based chemotherapy ± whole brain radiation; median survival ~3–5 years with treatment.

10 Intracranial Aneurysms & Subarachnoid Hemorrhage

Intracranial aneurysms are present in ~2–3% of the general population. Most are saccular ("berry") aneurysms at arterial bifurcations in the Circle of Willis. Risk factors for rupture: size (>7 mm significantly increases risk), location (posterior circulation, PComm), hypertension, smoking, family history, and conditions such as autosomal dominant polycystic kidney disease and Ehlers-Danlos type IV.

Subarachnoid Hemorrhage (SAH)

Rupture of an intracranial aneurysm causes SAH in ~85% of non-traumatic cases. Classic presentation: "worst headache of my life" (thunderclap headache), with or without loss of consciousness, nausea, meningismus, photophobia, and focal neurologic deficits. Mortality is ~30–40% overall; ~15% die before reaching the hospital.

Grading Scales

SAH Management

Unruptured Intracranial Aneurysms — Management

The decision to treat an unruptured aneurysm balances the natural history risk of rupture against the procedural risk of treatment. Risk factors for rupture (PHASES score): Population (Japanese/Finnish highest risk), Hypertension, Age (>70 increases risk), Size (≥7 mm significantly higher risk; <7 mm AComm/PComm also higher risk than other locations), Earlier SAH (from another aneurysm), and Site (posterior circulation, PComm highest risk). The ISUIA (International Study of Unruptured Intracranial Aneurysms) provided key natural history data: for anterior circulation aneurysms <7 mm without prior SAH, the 5-year rupture risk is ~0%; however, this has been debated, and many small aneurysms do rupture. Treatment options: microsurgical clipping (definitive, durable, low retreatment rate but requires craniotomy), endovascular coiling (less invasive, higher retreatment rate ~17% at 5 years), flow diverter stents (Pipeline Embolization Device — for large, wide-necked ICA aneurysms; promotes endoluminal reconstruction; requires dual antiplatelet therapy for 6+ months), or observation with serial imaging (for small, asymptomatic aneurysms in low-risk locations in elderly patients).

SAH Complications Summary

11 Arteriovenous Malformations & Cavernous Malformations

Arteriovenous Malformations (AVMs)

AVMs are congenital tangles of abnormal arteries and veins without an intervening capillary bed, resulting in high-flow arteriovenous shunting. The nidus is the core of the AVM. Annual hemorrhage risk is ~2–4% per year (higher with prior hemorrhage, deep location, deep venous drainage, and associated aneurysms). Presentation: hemorrhage (~50%), seizures (~25%), headache, progressive neurologic deficit ("steal" phenomenon).

Spetzler-Martin Grading

Total score 1–5. Grade I–II: microsurgical resection is first-line (low morbidity, ~96–100% cure rate). Grade III: multimodality treatment — consider embolization + surgery, or radiosurgery for small nidi. Grade IV–V: high surgical risk; observation often preferred unless hemorrhage occurs; ARUBA trial showed better outcomes with medical management alone vs intervention in unruptured AVMs at 33-month follow-up (controversial, debated long-term applicability — ARUBA, PMID: 24444842).

Cavernous Malformations (Cavernomas)

Clusters of thin-walled, endothelium-lined sinusoidal channels without intervening brain parenchyma (no smooth muscle or elastic fibers). Low-flow lesions, angiographically occult ("occult vascular malformations"). Prevalence ~0.5%. MRI appearance: "popcorn" or "mulberry" on T2, with characteristic hemosiderin ring (dark rim on T2/GRE/SWI). Can be sporadic (single) or familial (multiple — autosomal dominant mutations in CCM1/KRIT1, CCM2, CCM3). Annual symptomatic hemorrhage rate ~0.5–1% per lesion per year (higher after initial hemorrhage, ~4.5%/year). Presentation: seizures (most common), hemorrhage, focal neurologic deficits. Treatment: surgical resection for accessible, symptomatic lesions (especially with recurrent hemorrhage or drug-resistant epilepsy); observation for deep-seated or brainstem lesions with minimal symptoms. Radiosurgery is controversial (may reduce rebleeding risk for inoperable brainstem cavernomas).

12 Stroke — Surgical Management

Decompressive Craniectomy for Malignant MCA Infarction

Large MCA territory infarctions may develop life-threatening cerebral edema peaking at 2–5 days (malignant MCA syndrome, mortality up to 80% with medical management alone). Decompressive hemicraniectomy (≥12 cm diameter bone flap removal with duraplasty) within 48 hours reduces mortality from ~78% to ~29% in patients ≤60 years (pooled analysis of DECIMAL, DESTINY, and HAMLET trials — PMID: 17290030). However, many survivors have significant disability (mRS 4). DESTINY II showed benefit even in patients >60 years, though severe disability rates are higher (DESTINY II, PMID: 24694544). Patient/family goals-of-care discussion is essential.

Posterior Fossa Stroke

Cerebellar infarctions and hemorrhages carry a risk of rapid deterioration due to brainstem compression and obstructive hydrocephalus. Indications for suboccipital decompressive craniectomy: GCS decline, radiographic brainstem compression, acute hydrocephalus not responding to EVD alone. EVD placement alone may be sufficient for hydrocephalus without mass effect, but carries a risk of upward herniation if posterior fossa mass effect is not addressed.

Intracerebral Hemorrhage — Surgical Evacuation

The role of surgery for spontaneous ICH remains debated. The STICH trial showed no benefit of early surgical evacuation over medical management for deep ICH (STICH, PMID: 15639681). STICH II suggested possible benefit for superficial lobar hemorrhage (within 1 cm of cortical surface) in patients with GCS ≥9, though results were not statistically significant (STICH II, PMID: 23726393). MISTIE III evaluated minimally invasive catheter-based evacuation with alteplase — did not meet primary endpoint but subgroup analysis suggested benefit when ≥70% of clot is removed. Cerebellar hemorrhage >3 cm with brainstem compression is a class I indication for surgical evacuation.

Carotid Endarterectomy (CEA) & Stenting (CAS)

CEA is indicated for symptomatic carotid stenosis ≥50% (NASCET criteria — NASCET, PMID: 1852179) and asymptomatic carotid stenosis ≥60–70% in good surgical candidates with >5-year life expectancy (ACAS/ACST). CAS is an alternative for patients with hostile neck anatomy, prior neck radiation, or high surgical risk. The procedure should be performed within 2 weeks of the index event for symptomatic stenosis for maximum benefit.

CEA Surgical Technique

The patient is positioned supine with the head turned to the contralateral side. An incision is made along the anterior border of the sternocleidomastoid. The common carotid artery, internal carotid artery, and external carotid artery are exposed and controlled. Systemic heparin is given (5,000–8,000 units, ACT >250). Clamps are placed on the ICA, CCA, and ECA. An arteriotomy is made and the atherosclerotic plaque is dissected from the vessel wall in the endarterectomy plane (media-adventitia). The distal endpoint is carefully feathered to avoid a flap. Closure: primary closure or patch angioplasty (Dacron or bovine pericardium — patch closure reduces restenosis and perioperative stroke risk). A shunt (Javid, Pruitt-Inahara) may be placed during clamping to maintain cerebral perfusion — indications include: stump pressure <40–50 mmHg, contralateral carotid occlusion, EEG changes during clamping, or surgeon preference (routine shunting). Postoperative monitoring: frequent neurologic checks (stroke), blood pressure management (avoid hypertension → reperfusion hemorrhage; avoid hypotension → ischemia), and neck hematoma surveillance (expanding hematoma = emergent OR for wound exploration — can cause airway compromise).

Endovascular Thrombectomy for Acute Ischemic Stroke

Mechanical thrombectomy for large-vessel occlusion (LVO) stroke is one of the most impactful advances in neurosurgery/neurointerventional radiology. Five landmark trials in 2015 (MR CLEAN, ESCAPE, EXTEND-IA, SWIFT PRIME, REVASCAT) demonstrated overwhelming benefit of endovascular thrombectomy + IV tPA vs IV tPA alone for anterior circulation LVO within 6 hours of symptom onset. The DAWN and DEFUSE 3 trials extended the treatment window to 24 hours in select patients with favorable perfusion imaging (small ischemic core with large penumbra — "mismatch" profile). Stent retriever (Solitaire, Trevo) and aspiration catheter (ADAPT technique, Penumbra) approaches are used. Target: TICI 2b/3 reperfusion (successful recanalization). NNT ~2.6 for reduced disability (one of the lowest in medicine).

13 Degenerative Disc Disease & Cervical Myelopathy

Cervical Radiculopathy

Most commonly caused by posterolateral disc herniation or foraminal stenosis from osteophytes. Presents with arm pain in a dermatomal distribution, sensory changes, and weakness corresponding to the affected nerve root (see Section 02 Nerve Root Localization table). Natural history is favorable — ~75% improve with conservative management (physical therapy, NSAIDs, epidural steroid injections). Surgical indications: failure of 6–12 weeks conservative management, progressive neurologic deficit, or intractable pain.

Anterior Cervical Discectomy and Fusion (ACDF)

The most common cervical spine procedure. Approach through a transverse skin incision on the left side of the neck (to avoid the recurrent laryngeal nerve, which loops lower and is more variable on the right). Platysma is divided, the plane between the carotid sheath laterally and the trachea/esophagus medially is developed. Longus colli muscles are retracted to expose the anterior spine. The disc is removed, osteophytes are drilled, and the neural foramen is decompressed. An interbody graft (structural allograft, PEEK cage, or cage filled with bone graft) is placed, often with an anterior cervical plate for stabilization. Fusion rates >95% for single-level ACDF.

Cervical Myelopathy

Compression of the spinal cord, most commonly from cervical spondylosis (disc-osteophyte complexes, ligamentum flavum hypertrophy, ossification of the posterior longitudinal ligament — OPLL). Presents insidiously with gait difficulty (wide-based, spastic), hand clumsiness (difficulty with buttons, writing), upper motor neuron signs (hyperreflexia, Hoffman sign, Babinski sign, clonus), and sensory changes. Natural history is progressive — surgery is recommended for moderate-to-severe myelopathy or progressive symptoms.

Surgical approaches: Anterior — ACDF (1–2 levels), anterior cervical corpectomy and fusion (ACCF, for retrovertebral compression), or multi-level ACDF. Posterior — laminectomy with lateral mass fusion (for ≥3 levels, maintained lordosis), or laminoplasty (open-door or French-door technique — expands the canal without fusion, preserves motion; best for 3–5 levels with maintained lordosis). Anterior approach is preferred for 1–2 levels or when the compressive pathology is anterior (disc, OPLL). Posterior approach is preferred for ≥3 levels with maintained lordosis. Combined anterior-posterior surgery may be needed for severe multilevel disease with kyphosis.

Cervical Disc Arthroplasty

Motion-preserving alternative to ACDF for single or two-level cervical radiculopathy or myelopathy. Multiple FDA-approved devices (Prestige LP, ProDisc-C, Mobi-C). Contraindications include significant facet arthropathy, instability, and osteoporosis. Long-term data shows non-inferiority to ACDF with potential reduction in adjacent segment disease rates.

Ossification of the Posterior Longitudinal Ligament (OPLL)

Progressive ossification of the PLL causes cervical myelopathy, predominantly in East Asian populations. Classification (by CT morphology): continuous (worst prognosis, extends across multiple segments), segmental, mixed, and localized. OPLL occupying >60% of the canal diameter is generally considered an indication for surgery. Anterior surgery (corpectomy) directly removes the compressive OPLL but carries higher risk of CSF leak (the dura may be adherent to or ossified with the OPLL — "dural ossification"). Posterior surgery (laminoplasty or laminectomy with fusion) indirectly decompresses by allowing the cord to drift posteriorly — generally preferred for multilevel OPLL in patients with maintained lordosis. For OPLL extending beyond the vertebral body margin ("hill-shaped"), anterior approaches may be needed regardless.

14 Lumbar Stenosis & Spondylolisthesis

Lumbar Spinal Stenosis

Narrowing of the spinal canal, lateral recesses, or neural foramina, most commonly from degenerative changes (facet hypertrophy, ligamentum flavum thickening, disc bulging). Classic presentation: neurogenic claudication — bilateral leg pain, heaviness, and numbness with walking, relieved by sitting or forward flexion (increased canal diameter in flexion). Must be distinguished from vascular claudication (pain with walking, relieved by standing still, absent pedal pulses, ABI <0.9).

Conservative management: physical therapy, epidural steroid injections. The SPORT trial showed that surgical decompression (laminectomy) provides significant benefit over non-operative treatment at 2 and 4 years, with some crossover benefit at 8 years (SPORT for stenosis, PMID: 18299459). Standard procedure: lumbar laminectomy (removal of the lamina and ligamentum flavum to decompress the thecal sac and nerve roots). Fusion is added when there is associated instability or spondylolisthesis.

Lumbar Disc Herniation

Most commonly at L4–L5 and L5–S1. The posterolateral direction of herniation compresses the traversing nerve root. Surgical indications: cauda equina syndrome (emergency), progressive neurologic deficit, or failure of 6 weeks of conservative management. Standard procedure: microdiscectomy (microscope or loupe-assisted, hemilaminotomy, removal of the herniated disc fragment). Success rates ~85–95% for leg pain relief. Recurrence rate ~5–15%.

Spondylolisthesis

Forward slippage of one vertebral body on another. Classification by Meyerding grade: Grade I = 0–25%, Grade II = 25–50%, Grade III = 50–75%, Grade IV = 75–100%, Grade V (spondyloptosis) = >100%.

Surgical management: decompression alone may suffice for low-grade degenerative spondylolisthesis with stenosis, but fusion is typically added (posterior lumbar interbody fusion — PLIF, or transforaminal lumbar interbody fusion — TLIF). The SLIP II trial is evaluating the role of fusion for grade I degenerative spondylolisthesis. Isthmic spondylolisthesis failing conservative treatment is managed with posterolateral or interbody fusion. High-grade slips (III–V) require instrumented fusion with reduction consideration.

Lumbar Fusion Approaches

15 Spinal Cord Tumors

Classification by Compartment

Metastatic Spinal Cord Compression (MSCC)

A neurosurgical/oncologic emergency. Most commonly from lung, breast, prostate, kidney, and myeloma. Presents with progressive back pain (worse supine, worse with Valsalva), followed by weakness, sensory level, and bowel/bladder dysfunction. The Tokuhashi score helps predict prognosis and guide operative vs palliative approach. The NOMS framework (Neurologic, Oncologic, Mechanical instability, Systemic disease) guides decision-making. The Patchell randomized trial demonstrated that direct decompressive surgery + RT was superior to RT alone for maintaining ambulatory status in MSCC (Patchell 2005, PMID: 15689584).

16 Traumatic Brain Injury Emergency

Epidural Hematoma (EDH)

Arterial bleeding between the skull and dura, most commonly from rupture of the middle meningeal artery following a temporal bone fracture. Classic (but not always present) presentation: loss of consciousness → lucid interval → rapid deterioration with contralateral hemiparesis and ipsilateral pupil dilation (uncal herniation). CT shows a biconvex (lenticular) hyperdense collection that does not cross suture lines (dura is tightly adherent at sutures). Surgical indication: thickness >15 mm, midline shift >5 mm, or neurologic deterioration. Treatment: emergent craniotomy with hematoma evacuation and coagulation of the middle meningeal artery. Prognosis is excellent with prompt surgery (mortality <5% for uncomplicated EDH with early intervention).

Acute Subdural Hematoma (aSDH)

Venous bleeding from torn bridging veins between the cortex and dural sinuses, or from cortical arterial laceration. More common and more lethal than EDH. Associated with higher-energy mechanisms and often with underlying brain injury. CT shows a crescent-shaped hyperdense collection conforming to the brain surface, crossing suture lines. Surgical indications (BTF): thickness >10 mm, midline shift >5 mm, or GCS decline by ≥2 points. Treatment: emergent large trauma craniectomy/craniotomy with hematoma evacuation. Mortality remains high (~40–60%) due to associated parenchymal injury. Time from injury to surgery is critical — "the 4-hour rule" — mortality increases sharply when surgery is delayed beyond 4 hours (PMID: 16534088).

Chronic Subdural Hematoma (cSDH)

Occurs primarily in elderly, anticoagulated, or brain-atrophied patients. Develops over weeks following minor or unrecalled trauma. Bridging veins are stretched over the atrophied brain and tear easily. The hematoma develops a neomembrane with fragile capillaries that repeatedly bleed. CT shows a crescent-shaped hypodense or isodense collection (hyperdense if acute-on-chronic). Presentation: headache, cognitive decline, gait disturbance, hemiparesis. Treatment: burr hole drainage (1–2 burr holes with irrigation and subdural drain placement for 24–48 hours) — success rate ~80–90%. Craniotomy for recurrence, organized/loculated collections, or acute-on-chronic SDH. Middle meningeal artery embolization (MMAE) is an emerging treatment for preventing recurrence — the EMBOLISE trial showed significantly reduced recurrence and repeat surgery (EMBOLISE, PMID: 37856610).

Diffuse Axonal Injury (DAI)

Caused by rotational acceleration-deceleration forces shearing white matter axons. Grades: Grade 1 — gray-white matter junction (frontal, temporal); Grade 2 — corpus callosum (especially splenium); Grade 3 — dorsolateral brainstem (worst prognosis). CT may appear normal or show small punctate hemorrhages; MRI (especially SWI/DWI sequences) is more sensitive. No surgical treatment — management is supportive with ICP management as needed. Prognosis ranges from good recovery (mild DAI) to vegetative state or death (severe DAI with brainstem involvement).

Traumatic Contusions

Bruising of the brain parenchyma, most commonly in the frontal and temporal poles (brain impacts the rough anterior and middle cranial fossa floor). Coup contusions occur at the impact site; contrecoup contusions occur opposite the impact. May expand ("blossom") over 24–48 hours — repeat imaging is essential. Surgical evacuation is considered if the contusion is >50 mL, causes >5 mm midline shift, or the patient deteriorates neurologically.

Skull Fractures

Penetrating TBI

Most commonly from gunshot wounds. Management: aggressive resuscitation, seizure prophylaxis (7 days), broad-spectrum antibiotics, CT to define projectile trajectory and associated injuries. Surgical indications: accessible hematoma with mass effect, debridement of necrotic tissue and accessible bone/projectile fragments (do NOT probe deep for projectiles), watertight dural closure. Objects in situ should not be removed outside the OR. Vascular imaging (CTA or angiography) is recommended to evaluate for traumatic aneurysm or vascular injury. Mortality is ~90% for bihemispheric, transventricular, or dominant-hemisphere gunshot wounds.

17 Spinal Trauma & Spinal Cord Injury

ASIA (American Spinal Injury Association) Impairment Scale

Cervical Spine Fractures

Atlas (C1) fractures: Jefferson fracture = burst fracture of the C1 ring from axial loading. The rule of Spence: if total lateral mass overhang >6.9 mm on open-mouth odontoid view, the transverse ligament is likely ruptured (unstable) — requires surgery. Stable Jefferson fractures are treated with a rigid cervical collar or halo vest.

Axis (C2) fractures: Odontoid (dens) fractures — Anderson-D'Alonzo classification: Type I = tip avulsion (stable, rare); Type II = base of the dens (most common, highest nonunion rate ~40% — treat with anterior odontoid screw or posterior C1–C2 fusion); Type III = extends into the C2 body (usually heals with external immobilization). Hangman's fracture = bilateral C2 pars interarticularis fracture (traumatic spondylolisthesis of C2). Levine-Edwards classification: Type I = <3 mm displacement, no angulation (rigid collar); Type II = >3 mm displacement and angulation (halo or surgery); Type IIA = minimal displacement, significant angulation (traction contraindicated — causes distraction; treat with halo or surgery); Type III = associated facet dislocation (requires surgery).

Subaxial Cervical Spine Injury Classification (SLICS)

SLICS Score: ≤3 = non-operative; 4 = equivocal; ≥5 = surgical.

Thoracolumbar Injury Classification & Severity Score (TLICS)

TLICS Score: ≤3 = non-operative; 4 = equivocal; ≥5 = surgical.

Cervical Spine Clearance

Spinal Shock vs Neurogenic Shock

18 Deep Brain Stimulation & Functional Procedures

Deep Brain Stimulation (DBS)

DBS involves the stereotactic implantation of electrodes into specific deep brain nuclei, connected to a subcutaneously placed pulse generator (similar to a cardiac pacemaker). The mechanism involves modulation (not ablation) of pathologic neural circuit activity.

Ablative Procedures

With the advent of DBS and MRI-guided focused ultrasound (MRgFUS), radiofrequency ablation has become less common but remains relevant. MRgFUS thalamotomy (Exablate Neuro) is FDA-approved for essential tremor and tremor-dominant PD — incisionless ablation of the VIM nucleus using convergent ultrasound beams under real-time MRI thermometry. Pallidotomy (GPi ablation) is occasionally used for Parkinson's dyskinesia in patients who are not DBS candidates.

Other Functional Procedures

Trigeminal neuralgia: Microvascular decompression (MVD) is the gold-standard surgical treatment for medication-refractory trigeminal neuralgia — a vascular loop (usually the SCA) is separated from the trigeminal nerve root entry zone with a Teflon pad (pain-free rate ~80% at 5 years). Percutaneous procedures (radiofrequency rhizotomy, glycerol rhizolysis, balloon compression) and stereotactic radiosurgery are alternatives for patients who are poor surgical candidates. Hemifacial spasm: MVD (offending vessel, usually AICA or PICA, compressing CN VII at the root exit zone) is the definitive treatment.

Spasticity Management

Intrathecal baclofen pump (ITB): a programmable pump (placed subcutaneously in the abdomen) delivers baclofen directly into the CSF via a catheter in the lumbar intrathecal space. Indicated for severe spasticity from spinal cord injury, cerebral palsy, multiple sclerosis, or stroke that is refractory to oral medications. A screening trial (50–100 mcg intrathecal baclofen via lumbar puncture) must demonstrate ≥1-point reduction on the Ashworth scale before permanent implantation. Complications: catheter malfunction (kinking, migration, disconnection — most common), infection, overdose (flaccidity, respiratory depression, coma — treated with airway support), and withdrawal syndrome (rebound spasticity, hyperthermia, rhabdomyolysis, multiorgan failure, death — treat with oral/enteral baclofen, benzodiazepines, ICU monitoring; can mimic malignant hyperthermia or neuroleptic malignant syndrome).

Selective dorsal rhizotomy (SDR): selective sectioning of dorsal (sensory) rootlets L1–S1 to reduce afferent input driving spasticity. Primarily used in children with spastic diplegic cerebral palsy (ambulatory children ages 3–8 with predominantly lower-extremity spasticity and good underlying strength). Intraoperative EMG is used to identify and selectively cut the rootlets with the most abnormal responses (sustained, spreading activity). Significant reduction in spasticity with preserved motor strength; requires intensive post-operative physiotherapy.

Pain Procedures

Spinal cord stimulation (SCS): epidural electrode placement over the dorsal columns; generates paresthesias that mask pain signals. Indications: failed back surgery syndrome (FBSS), complex regional pain syndrome (CRPS), peripheral neuropathy, refractory angina. Trial phase (temporary electrode) precedes permanent implantation — ≥50% pain relief defines a successful trial. High-frequency (10 kHz) and burst stimulation paradigms provide paresthesia-free analgesia. Motor cortex stimulation (MCS): epidural electrode over the precentral gyrus for refractory central pain syndromes (thalamic pain, post-stroke pain, trigeminal neuropathic pain). Intrathecal drug delivery: morphine, ziconotide (non-opioid calcium channel blocker), or bupivacaine delivered via implanted pump for cancer-related pain or refractory non-malignant pain.

19 Epilepsy Surgery

Epilepsy surgery is indicated for drug-resistant epilepsy (failure of ≥2 appropriate antiseizure medications at adequate doses). Approximately one-third of epilepsy patients are drug-resistant. Presurgical evaluation includes: video-EEG monitoring (seizure semiology and EEG localization), MRI (structural lesion identification — hippocampal sclerosis, cortical dysplasia, tumor, vascular malformation), PET (interictal hypometabolism), neuropsychological testing, WADA test or fMRI (language and memory lateralization), and potentially invasive EEG monitoring (subdural grids, stereo-EEG — SEEG).

Surgical Procedures

Neuromodulation for Epilepsy

Vagus nerve stimulation (VNS): left vagus nerve electrode connected to a chest-wall pulse generator; reduces seizure frequency by ~50% in ~50% of patients (palliative, not curative). Mechanism not fully understood — activates brainstem nuclei that modulate cortical excitability. Responsive neurostimulation (RNS, NeuroPace): closed-loop device implanted at the seizure focus that detects abnormal ECoG activity and delivers targeted electrical stimulation to abort seizures. Median seizure reduction ~50–60% at 2 years. Deep brain stimulation of the anterior nucleus of the thalamus (ANT-DBS): SANTE trial showed ~56% seizure reduction at 2 years (SANTE, PMID: 20307616).

Engel Outcome Classification

Temporal Lobe Epilepsy — Mesial Temporal Sclerosis

Mesial temporal sclerosis (MTS) is the most common pathologic substrate of drug-resistant temporal lobe epilepsy. Characterized histologically by hippocampal neuronal loss (especially CA1 and CA3 subfields) and gliosis. MRI findings: hippocampal atrophy (decreased volume on coronal T1), increased T2/FLAIR signal in the hippocampus, and loss of internal hippocampal architecture. Clinical presentation: complex partial seizures (now termed "focal impaired awareness seizures") with an aura (epigastric rising sensation, fear, deja vu), followed by behavioral arrest, oroalimentary automatisms (lip-smacking, chewing), and contralateral hand automatisms with ipsilateral hand dystonia. Scalp EEG shows ipsilateral temporal epileptiform discharges. Surgical treatment (ATL or SAH) is the most effective treatment for drug-resistant TLE — the ERSET trial demonstrated superiority of surgery over continued medical therapy (Engel I outcome: 58% surgery vs 8% medical — ERSET, PMID: 22150006).

20 Hydrocephalus

Classification

Obstructive (non-communicating): blockage within the ventricular system (e.g., aqueductal stenosis, posterior fossa tumor obstructing the fourth ventricle, colloid cyst blocking the foramen of Monro). Communicating: impaired CSF absorption at the arachnoid granulations (post-SAH, post-meningitis, post-hemorrhage) or, rarely, CSF overproduction (choroid plexus papilloma). Ex vacuo: ventriculomegaly from brain parenchymal loss (atrophy) — NOT true hydrocephalus (no elevated pressure).

Treatment Options

Ventriculoperitoneal (VP) shunt: the most common definitive treatment. A ventricular catheter (typically right frontal via Kocher's point or right parieto-occipital via Keen's point) is connected to a one-way pressure-regulated valve, which drains via a distal catheter into the peritoneal cavity. Complications: obstruction (~30% at 1 year — most common cause of shunt failure; proximal catheter occlusion by choroid plexus is the most common site), infection (~5–10%, usually within 6 months; most common organisms: Staphylococcus epidermidis and S. aureus; treatment: shunt removal + external drainage + IV antibiotics for 10–14 days, then new shunt), over-drainage (slit ventricle syndrome, subdural hygromas/hematomas; prevented by programmable valves or antisiphon devices).

Endoscopic third ventriculostomy (ETV): endoscopic fenestration of the floor of the third ventricle, creating a direct communication between the third ventricle and the prepontine cistern, bypassing the aqueduct. Best for obstructive hydrocephalus (aqueductal stenosis). The ETV Success Score (ETVSS) predicts success based on age, etiology, and prior shunt: higher scores predict greater success. ETV may be combined with choroid plexus cauterization (ETV/CPC) in infants.

Normal Pressure Hydrocephalus (NPH)

A form of communicating hydrocephalus in elderly patients. Classic triad (Hakim's triad): gait disturbance (wide-based, magnetic, shuffling — earliest and most responsive to treatment), urinary incontinence, and dementia (subcortical pattern — psychomotor slowing; latest and least responsive to treatment). Mnemonic: "wet, wacky, wobbly." Imaging: ventriculomegaly disproportionate to sulcal atrophy (Evans' index = maximal bicaudate diameter / maximal inner skull diameter >0.3). Diagnostic workup: large-volume lumbar puncture (30–50 mL CSF removal) — improvement in gait within 1–4 hours predicts shunt response (~80% positive predictive value). Extended lumbar drainage (3–5 days) is more sensitive. Treatment: VP shunt with a programmable valve (allows adjustment if over- or under-drainage occurs). Gait improves in ~80% of properly selected patients; cognitive improvement is less reliable.

Idiopathic Intracranial Hypertension (Pseudotumor Cerebri)

Elevated ICP without hydrocephalus, mass lesion, or abnormal CSF composition. Predominantly affects obese women of childbearing age. Modified Dandy criteria: symptoms/signs of elevated ICP (headache, papilledema, visual obscurations, CN VI palsy), elevated opening pressure on LP (>25 cmH₂O), normal CSF composition, normal neuroimaging (may show empty sella, optic nerve sheath distension, transverse sinus stenosis on MRV). Medical treatment: weight loss, acetazolamide (reduces CSF production; 500 mg BID, titrate up to 2 g/day), topiramate (adjunct — also promotes weight loss). Surgical options for refractory cases or progressive visual loss: optic nerve sheath fenestration (ONSF — protects vision but may not relieve headache) or CSF diversion (VP shunt or LP shunt). Venous sinus stenting is an emerging treatment for patients with documented transverse sinus stenosis and pressure gradient >8 mmHg.

Slit Ventricle Syndrome

A complication of chronic VP shunt over-drainage, most commonly in children. Small slit-like ventricles with intermittent shunt obstruction cause episodic headaches, nausea, and lethargy. CT shows collapsed ventricles. The shunt cannot drain effectively because the choroid plexus and ependyma occlude the ventricular catheter tip. Management: programmable valve with higher opening pressure, antisiphon device, shunt revision with catheter repositioning, subtemporal decompression, or ETV (shunt independence).

21 Pediatric Neurosurgery

Craniosynostosis

Premature fusion of one or more cranial sutures, resulting in abnormal head shape. Incidence ~1 in 2,000 births. Classified by the suture involved:

Surgical treatment: open cranial vault remodeling (typically at 6–12 months) or endoscopic strip craniectomy with post-operative helmet therapy (best if performed before 3–4 months of age). Endoscopic approaches are less invasive with shorter hospital stays but require compliant helmet wear for months.

Chiari Malformations

Chiari I: tonsillar ectopia ≥5 mm below the foramen magnum. May be asymptomatic (incidental finding on MRI). Symptomatic patients present with suboccipital headache (worsened by Valsalva, cough, straining), neck pain, and may develop syringomyelia (cavitation of the spinal cord from altered CSF dynamics). Treatment: posterior fossa decompression (suboccipital craniectomy + C1 laminectomy ± duraplasty). Chiari II: associated with myelomeningocele; hindbrain herniation includes the cerebellar vermis, fourth ventricle, and lower brainstem through the foramen magnum. Chiari III: rare; herniation of posterior fossa contents into an occipitocervical encephalocele.

Myelomeningocele (Open Neural Tube Defect)

The most common open neural tube defect. Results from failure of posterior neural tube closure during the 4th week of gestation. The exposed neural placode is covered by a meningeal sac. ~90% are associated with Chiari II malformation and ~80% develop hydrocephalus requiring shunt placement. Prevention: maternal folic acid supplementation (0.4 mg/day preconception; 4 mg/day if prior affected pregnancy). Postnatal repair within 24–72 hours (closure of the neural placode and overlying layers). Prenatal repair (MOMS trial — PMID: 21306277) at 19–25 weeks gestation showed reduced need for shunting and improved motor outcomes at 30 months but increased risk of preterm delivery.

Tethered Cord Syndrome

The spinal cord is abnormally attached, restricting its normal ascent during growth. Causes: thick filum terminale (most common), lipomyelomeningocele, split cord malformation (diastematomyelia), dermoid/epidermoid, prior myelomeningocele repair. Presentation in children: progressive lower extremity weakness, foot deformity (pes cavus), scoliosis, urologic dysfunction (incontinence, recurrent UTIs). In adults: back/leg pain, progressive lower extremity symptoms, urologic dysfunction. MRI shows a low-lying conus (below L2 in adults) and the tethering lesion. Treatment: surgical untethering (section of the filum terminale or release of the tethering lesion).

Pediatric Brain Tumors — Overview

Brain tumors are the most common solid tumors in children and the leading cause of cancer-related death in pediatrics. Unlike adults, the majority of pediatric brain tumors arise in the posterior fossa (~60%). The four most common types:

Arachnoid Cysts

Congenital, developmental CSF-filled cysts within the arachnoid membrane. Most common location: middle cranial fossa (Sylvian fissure). Usually incidental findings. Most are asymptomatic and require no treatment (serial imaging only). Indications for surgery: symptomatic (headache attributable to the cyst, focal deficit, seizures directly related), growing on serial imaging, or associated hydrocephalus. Surgical options: endoscopic fenestration (preferred — opens the cyst into the basal cisterns), craniotomy with cyst wall excision/marsupialization, or cystoperitoneal shunt (least preferred due to shunt dependence).

22 Craniotomy Approaches

Major Craniotomy Approaches

Patient Positioning

Proper head positioning is critical. The Mayfield head clamp (three-pin fixation) rigidly fixes the head for craniotomies. Positions: supine with head turned (pterional, frontal); lateral (park bench) (suboccipital, retrosigmoid); prone (midline suboccipital, posterior spine); sitting (posterior fossa — excellent gravity-assisted retraction, but risk of venous air embolism — requires precordial Doppler, end-tidal CO₂ monitoring, and central venous access for air aspiration).

23 Stereotactic & Endoscopic Neurosurgery

Stereotactic Surgery

Stereotactic surgery uses a coordinate system (frame-based or frameless) to precisely target intracranial structures for biopsy, ablation, or electrode placement. Frame-based stereotaxy: a rigid frame (Leksell, CRW, or BRW) is fixed to the skull with pins, providing a Cartesian coordinate system. CT or MRI is obtained with the frame and localizer in place. Target coordinates are calculated. Accuracy ~1–2 mm. Frameless stereotaxy (neuronavigation): uses fiducial markers or anatomic landmarks registered to preoperative imaging (CT, MRI). Systems include optical (infrared cameras tracking reflective spheres on instruments — Medtronic StealthStation, Brainlab) and electromagnetic tracking. Accuracy ~2–3 mm. Used routinely for craniotomy planning, biopsy guidance, and intraoperative orientation.

Stereotactic Brain Biopsy

Indicated when tissue diagnosis is needed and resection is not feasible (deep-seated lesions, eloquent cortex, multiple lesions, lymphoma suspected — steroids should be withheld until biopsy for suspected lymphoma). Diagnostic yield >95% for frame-based biopsies. Complications: hemorrhage (~2–5%, symptomatic ~1%), infection, neurologic deficit. The target should avoid vessels (plan trajectory on contrast-enhanced MRI), ventricles (risk of hemorrhage into the CSF), and eloquent structures.

Endoscopic Neurosurgery

Rigid or flexible endoscopes are used for intraventricular procedures: ETV (see Section 20), tumor biopsy and removal (intraventricular tumors, colloid cysts), cyst fenestration, septum pellucidotomy (for trapped lateral ventricle), and aqueductoplasty. The endoscopic endonasal approach (see Section 22) is an expanded-corridor endoscopic technique for skull base pathology. Advantages of endoscopy include illumination, angled views, and minimally invasive access. Limitations: limited instrument maneuverability, difficulty with hemostasis, and a learning curve.

Stereotactic Radiosurgery (SRS)

Single-fraction, high-dose focused radiation delivered with submillimeter accuracy. Platforms: Gamma Knife (201 cobalt-60 sources converging on a focal point; requires frame fixation; most commonly used for intracranial targets), CyberKnife (robotic LINAC; frameless; can treat cranial and spinal targets), LINAC-based SRS (using specialized collimation or multileaf collimators). Indications: brain metastases (1–10 lesions, ≤3 cm), vestibular schwannoma, meningioma (residual/recurrent), AVM (<3 cm nidus), trigeminal neuralgia, and selected pituitary adenomas. For AVMs, the obliteration rate after SRS is ~70–80% at 3 years for small nidi. The latency period (1–3 years for AVM obliteration) is a key limitation — the patient remains at risk of hemorrhage during this interval.

24 Minimally Invasive Spine Surgery

MIS Principles

Minimally invasive spine surgery (MISS) uses tubular retractors, endoscopes, and specialized instruments to achieve the same surgical goals (decompression, fusion, stabilization) through smaller incisions with less muscle disruption. Benefits: reduced blood loss, shorter hospital stay, less postoperative pain, faster recovery. Drawbacks: steep learning curve, limited visualization, increased radiation exposure (fluoroscopy dependence).

Key MIS Procedures

MIS microdiscectomy: tubular retractor placed through a ~2 cm incision; microscope or endoscope used for disc removal. Outcomes equivalent to open microdiscectomy with less tissue damage. MIS TLIF (transforaminal lumbar interbody fusion): performed through a tubular retractor; percutaneous pedicle screws placed under fluoroscopic guidance; interbody cage placed through a unilateral transforaminal approach. Endoscopic spine surgery: full-endoscopic discectomy (transforaminal or interlaminar approach) using a working-channel endoscope; performed under local anesthesia or conscious sedation in some centers. Percutaneous pedicle screw fixation: screws placed through stab incisions under fluoroscopy guidance (K-wire, cannulated screw technique); used for trauma stabilization, tumor stabilization, and as part of MIS fusion constructs. Lateral interbody fusion (XLIF/LLIF): retroperitoneal, transpsoas approach to the lumbar disc space; allows placement of a large interbody cage for indirect decompression and coronal/sagittal correction; risk of lumbar plexus injury (neuromonitoring required); cannot be performed at L5–S1 (iliac crest blocks access).

Robotic-Assisted Spine Surgery

Robotic systems (Mazor X, ExcelsiusGPS, ROSA Spine) assist with pedicle screw placement through preoperative CT-based planning and intraoperative guidance. Studies show improved accuracy of screw placement (>98% accuracy vs ~92% freehand) with potential reduction in revision surgery, though operative time may be increased during the learning curve.

Spinal Fusion — Instrumentation Principles

Pedicle screws are the workhorse of spinal fixation — inserted through the pedicle into the vertebral body, providing three-column fixation. Screw diameter should be ~80% of the pedicle width. Placement techniques: freehand (anatomic landmarks — entry point at the junction of the transverse process and superior articular process for lumbar; use a gearshift to cannulate the pedicle), fluoroscopy-guided, navigation-guided, or robot-assisted. Lateral mass screws are used in the cervical spine (C3–C6); the Magerl technique is most common (entry point at center of lateral mass, aimed 25° lateral and 45° cephalad). C1 lateral mass screws and C2 pedicle or pars screws (Harms technique) are used for atlantoaxial fixation. Interbody cages (PEEK, titanium, or 3D-printed) provide anterior column support, restore disc height, and contain bone graft to promote fusion.

25 Neuroimaging — CT, MRI, & Angiography

CT — Key Neurosurgical Applications

CT is the first-line imaging for acute neurosurgical emergencies. Non-contrast CT (NCCT): acute blood appears hyperdense (white) for approximately 1–2 weeks, then becomes isodense, then hypodense (chronic SDH is dark). Air (pneumocephalus) is hyperdense black. Bone is bright white. Key findings to identify: midline shift (measured at the septum pellucidum — >5 mm generally warrants surgical consideration), hydrocephalus (temporal horn dilation is an early sign), effacement of basal cisterns (impending herniation), skull fractures (linear, depressed, basilar). CT angiography (CTA): rapid assessment of cerebral vasculature — aneurysm detection, vessel occlusion (large-vessel stroke), vascular injury in trauma, and AVM characterization.

MRI — Key Sequences

Cerebral Angiography (DSA)

Digital subtraction angiography (DSA) remains the gold standard for cerebral vascular imaging. Indications: definitive characterization of aneurysms (morphology, neck, relationship to branches), AVM evaluation (feeding arteries, nidus, draining veins, flow dynamics), fistula evaluation, vasospasm assessment and treatment, and therapeutic intervention (coiling, embolization, thrombectomy, angioplasty). Complications: stroke (~0.5–1%), groin hematoma, dissection, contrast reactions.

Key Imaging Patterns — Differential Diagnosis

Brain Abscess — Neurosurgical Considerations

Brain abscesses are focal infections within the brain parenchyma, most commonly from contiguous spread (otitis media, sinusitis, dental infection), hematogenous dissemination (endocarditis, pulmonary AVM, IV drug use), or post-surgical/post-traumatic inoculation. Common organisms: Streptococcus spp. (most common), Staphylococcus aureus (post-surgical/traumatic), anaerobes, and polymicrobial. In immunocompromised: Toxoplasma (HIV, ring-enhancing, basal ganglia), Nocardia, Aspergillus. Treatment: antibiotics (empiric: third-gen cephalosporin + metronidazole ± vancomycin, for 6–8 weeks) + surgical drainage. Stereotactic aspiration is preferred for deep-seated or eloquent-area abscesses; craniotomy with excision for superficial, multiloculated, or fungal abscesses. Abscess ≥2.5 cm generally requires surgical intervention. Serial imaging to confirm response. Identify and treat the source (e.g., sinus, ear, dental).

26 Electrophysiological Monitoring

Intraoperative Neuromonitoring (IONM)

IONM is used during neurosurgical and spine procedures to detect impending neurologic injury in real time, allowing the surgeon to modify the approach before permanent damage occurs.

27 Antiepileptics & Osmotic Agents

Antiepileptic Drugs (AEDs) in Neurosurgery

Osmotic Agents

28 Steroids, Anticoagulation Reversal, & Chemotherapy

Dexamethasone

The primary corticosteroid used in neurosurgery. Mechanism: reduces vasogenic edema by stabilizing the blood-brain barrier (decreases capillary permeability). Onset ~4–6 hours for edema reduction (maximal effect 24–72 hours). Dosing: brain tumors with edema — 10 mg IV loading dose, then 4 mg IV/PO q6h; taper as symptoms allow. Spinal cord compression — 10 mg IV bolus, then 4–6 mg q6h. Key side effects: hyperglycemia (tight glucose control recommended — hyperglycemia worsens neurologic outcomes), GI hemorrhage (PPI prophylaxis), immunosuppression, myopathy (proximal weakness with chronic use), insomnia, psychosis, avascular necrosis, adrenal suppression (taper after prolonged use, do not stop abruptly).

Anticoagulation Reversal

Rapid reversal of anticoagulation is critical in patients with intracranial hemorrhage.

Chemotherapy — Temozolomide (TMZ)

The standard chemotherapy agent for gliomas (GBM and high-grade astrocytomas). Mechanism: alkylating agent that methylates DNA at O6-guanine, leading to mismatch repair-triggered apoptosis. Oral bioavailability ~100%; crosses the BBB effectively. Stupp protocol: concurrent phase — 75 mg/m²/day for 42 days during radiation; adjuvant phase — 150–200 mg/m²/day for 5 days per 28-day cycle, for 6–12 cycles. Key side effects: myelosuppression (lymphopenia — requires PJP prophylaxis with TMP-SMX during concurrent phase), nausea (antiemetic prophylaxis), fatigue, hepatotoxicity (monitor LFTs). MGMT promoter methylation is the strongest predictive biomarker for TMZ responsiveness — methylation silences the MGMT repair enzyme, rendering cells more susceptible to TMZ-induced DNA damage.

Other Agents

Bevacizumab (Avastin): anti-VEGF monoclonal antibody; FDA-approved for recurrent GBM. Reduces edema dramatically (steroid-sparing effect) and improves PFS, but does NOT improve overall survival. Risks: wound healing impairment (hold perioperatively), hemorrhage, thromboembolism, GI perforation. Lomustine (CCNU): nitrosourea alkylating agent used in combination with other agents (PCV regimen: procarbazine, CCNU, vincristine) for oligodendrogliomas and low-grade gliomas. Carmustine (BCNU) wafers (Gliadel): biodegradable polymer wafers impregnated with BCNU, placed in the resection cavity; modest survival benefit; risks include cerebral edema, seizures, and wound healing complications.

Perioperative Antibiotics

Standard prophylactic antibiotics for craniotomy: cefazolin 2 g IV within 60 minutes of incision (re-dose q4h for long cases or estimated blood loss >1500 mL). For patients with MRSA risk or beta-lactam allergy: vancomycin 15 mg/kg IV (begin infusion 120 minutes before incision to account for slow administration). For spinal surgery with instrumentation: cefazolin ± gentamicin powder applied locally (evidence for reduced SSI, though not universally adopted). Antibiotics are typically continued for 24 hours postoperatively (not extended further unless drains or EVD are in place — EVD-related infection prophylaxis protocols vary by institution).

Anticoagulation in Neurosurgical Patients

29 Classification Systems Master Table

30 Complications & Management

Surgical Site Infection

Craniotomy wound infection rate ~1–3%. Superficial wound infection: erythema, swelling, drainage — antibiotics ± wound opening and irrigation. Bone flap infection / osteomyelitis: requires bone flap removal, prolonged IV antibiotics (6–8 weeks), and delayed cranioplasty (typically 3–6 months later). Empyema (subdural or epidural): surgical drainage + IV antibiotics. Most common organisms: S. aureus, coagulase-negative staphylococci, Propionibacterium acnes (indolent — may present months after surgery with bone flap loosening).

CSF Leak

Occurs after skull base surgery (especially transsphenoidal), posterior fossa surgery, and spine surgery (durotomy). Post-craniotomy CSF leak presents as clear drainage from the wound or CSF rhinorrhea/otorrhea. Management: conservative — bed rest, head elevation, lumbar drain (CSF diversion to allow dural healing), acetazolamide (reduce CSF production); surgical repair if conservative measures fail. CSF leak after transsphenoidal surgery (~2–5%) — managed with lumbar drain and possible re-exploration for nasoseptal flap repair. Test for beta-2 transferrin or beta-trace protein to confirm CSF.

Postoperative Hemorrhage

May occur in the epidural, subdural, or intracerebral compartments after any intracranial procedure. Risk factors: coagulopathy, hypertension, incomplete hemostasis, tumor bed bleeding. Presentation: neurologic deterioration, headache, new deficit, or failure to awaken from anesthesia as expected. Management: emergent CT, correct coagulopathy, and re-exploration if hemorrhage causes mass effect or neurologic decline. Intraoperative hemostasis with bipolar cautery, hemostatic agents (Surgicel, Gelfoam, thrombin), and meticulous technique are preventive.

Cerebral Edema

Vasogenic edema: BBB disruption (tumors, infection, radiation necrosis) — responds to dexamethasone. Cytotoxic edema: cellular swelling from ischemia — does NOT respond to steroids (requires osmotic therapy, decompressive surgery). Interstitial (transependymal) edema: periventricular CSF seepage in hydrocephalus — treatment is CSF diversion.

Venous Thromboembolism (DVT/PE)

Neurosurgical patients are at high risk (~20–30% DVT rate without prophylaxis) due to immobility, surgery duration, malignancy, and paresis. Prevention: mechanical (SCDs, graduated compression stockings) starting on admission; pharmacologic (LMWH or UFH) initiated 24–48 hours postoperatively once hemostasis is confirmed. In brain tumor surgery, the risk of VTE (~20–30%) outweighs the risk of postoperative hemorrhage from prophylactic anticoagulation (~1–2%). Treatment of established DVT/PE requires systemic anticoagulation — timing must balance the risk of intracranial hemorrhage (usually safe to start 1–2 weeks after craniotomy if no hemorrhagic complications). IVC filter considered if anticoagulation is contraindicated.

Seizures

Postoperative seizures occur in ~5–20% of supratentorial craniotomies (higher with cortical tumors, intraoperative cortical manipulation, and prior seizure history). New-onset seizures require imaging to rule out hemorrhage, edema, or ischemia. Management: IV levetiracetam or lorazepam for acute seizure; AED adjustment as needed. Status epilepticus protocol: lorazepam → levetiracetam or fosphenytoin → if refractory, intubation and IV anesthetics (propofol, midazolam, or pentobarbital) with continuous EEG monitoring.

Neurological Deficit

May result from direct surgical injury, retraction injury, vascular compromise, or postoperative hemorrhage/edema. SMA syndrome: supplementary motor area retraction/resection causes contralateral akinesia and mutism, which is typically transient (resolves within days to weeks in most cases). Posterior fossa/cerebellar mutism syndrome: occurs in ~25% of pediatric posterior fossa tumor resections, typically 1–2 days postoperatively; characterized by mutism, emotional lability, hypotonia, and ataxia; recovery may take weeks to months and may be incomplete.

Hyponatremia in Neurosurgical Patients

Common and potentially dangerous. Two major mechanisms must be distinguished:

Diabetes Insipidus (DI) After Pituitary Surgery

Occurs in ~10–20% of patients after transsphenoidal surgery (usually transient). Caused by injury to the posterior pituitary or pituitary stalk, resulting in decreased ADH secretion. Presents with polyuria (>250 mL/hr or >3 L/day of dilute urine), hypernatremia, and intense thirst. Diagnostic criteria: urine specific gravity <1.005, urine osmolality <200 mOsm/kg, serum sodium >145 mEq/L. Treatment: DDAVP (desmopressin) 1–2 mcg IV/SC or 10–20 mcg intranasal; titrate to maintain Na 135–145; monitor closely for overcorrection (SIADH phase may follow). The classic "triphasic response" after stalk injury: DI (days 1–5) → SIADH (days 5–10, release of stored ADH from degenerating posterior pituitary) → permanent DI (after day 10 if stalk injury is severe). Not all patients exhibit all three phases.

Pseudomeningocele

A collection of CSF in the soft tissues outside the dura, usually following spine surgery (incidental durotomy) or posterior fossa surgery. Presents as a fluctuant subcutaneous swelling at the surgical site, headache, and wound drainage. Most small pseudomeningoceles resolve with conservative management (pressure dressing, bed rest, wound care). Large or symptomatic pseudomeningoceles may require lumbar drain placement or surgical repair of the dural defect.

31 Medications Master Table

32 Abbreviations Master List

References

Figures

• Figure 1 — Circle of Willis. Wikimedia Commons. Public domain.
• Figure 2 — Ventricular System. Gray's Anatomy (1918). Wikimedia Commons. Public domain.
• Figure 3 — Spinal Cord Cross-Section. Wikimedia Commons. Public domain.

Key Trials & Guidelines

• Stupp R, et al. Radiotherapy plus concomitant and adjuvant temozolomide for glioblastoma. N Engl J Med. 2005;352(10):987-996. PMID: 15758009
• Stummer W, et al. Fluorescence-guided surgery with 5-aminolevulinic acid for resection of malignant glioma. Lancet Oncol. 2006;7(5):392-401. PMID: 16456148
• Buckner JC, et al. Radiation plus procarbazine, CCNU, and vincristine in low-grade glioma (RTOG 9802). N Engl J Med. 2016;374(14):1344-1355. PMID: 27050206
• Molyneux AJ, et al. International Subarachnoid Aneurysm Trial (ISAT). Lancet. 2002;360(9342):1267-1274. PMID: 12414204
• Mohr JP, et al. Medical management with or without interventional therapy for unruptured brain arteriovenous malformations (ARUBA). Lancet. 2014;383(9917):614-621. PMID: 24444842
• Patchell RA, et al. A randomized trial of surgery in the treatment of single metastases to the brain. N Engl J Med. 1990;322(8):494-500. PMID: 2405271
• Brown PD, et al. Hippocampal avoidance during whole-brain radiotherapy plus memantine for patients with brain metastases (NRG CC001). J Clin Oncol. 2020;38(10):1019-1029. PMID: 31454575
• Cooper DJ, et al. Decompressive craniectomy in diffuse traumatic brain injury (DECRA). N Engl J Med. 2011;364(16):1493-1502. PMID: 21434843
• Hutchinson PJ, et al. Trial of decompressive craniectomy for traumatic intracranial hypertension (RESCUEicp). N Engl J Med. 2016;375(12):1119-1130. PMID: 27602507
• CRASH Trial Collaborators. Effect of intravenous corticosteroids on death within 14 days in 10,008 adults with clinically significant head injury. Lancet. 2004;364(9442):1321-1328. PMID: 15474134
• NASCET Collaborators. Beneficial effect of carotid endarterectomy in symptomatic patients with high-grade carotid stenosis. N Engl J Med. 1991;325(7):445-453. PMID: 1852179
• Vahedi K, et al. Early decompressive surgery in malignant infarction of the middle cerebral artery: pooled analysis. Lancet Neurol. 2007;6(3):215-222. PMID: 17290030
• Jüttler E, et al. Hemicraniectomy in older patients with extensive middle-cerebral-artery stroke (DESTINY II). N Engl J Med. 2014;370(12):1091-1100. PMID: 24694544
• Mendelow AD, et al. Early surgery versus initial conservative treatment in patients with spontaneous supratentorial intracerebral haematomas (STICH). Lancet. 2005;365(9457):387-397. PMID: 15639681
• Weinstein JN, et al. Surgical versus nonsurgical therapy for lumbar spinal stenosis (SPORT). N Engl J Med. 2008;358(8):794-810. PMID: 18299459
• Patchell RA, et al. Direct decompressive surgical resection in the treatment of spinal cord compression caused by metastatic cancer. Lancet. 2005;366(9486):643-648. PMID: 15689584
• Fehlings MG, et al. Early versus delayed decompression for traumatic cervical spinal cord injury (STASCIS). PLoS One. 2012;7(2):e32037. PMID: 22290395
• Fisher RS, et al. Electrical stimulation of the anterior nucleus of thalamus for treatment of refractory epilepsy (SANTE). Epilepsia. 2010;51(5):899-908. PMID: 20307616
• Adzick NS, et al. A randomized trial of prenatal versus postnatal repair of myelomeningocele (MOMS). N Engl J Med. 2011;364(11):993-1004. PMID: 21306277
• Temkin NR, et al. A randomized, double-blind study of phenytoin for the prevention of post-traumatic seizures. N Engl J Med. 1990;323(8):497-502. PMID: 2299096

Additional Key Trials

• Wiebe S, et al. A randomized, controlled trial of surgery for temporal-lobe epilepsy (ERSET). N Engl J Med. 2001;345(5):311-318. PMID: 22150006
• Berkhemer OA, et al. A randomized trial of intraarterial treatment for acute ischemic stroke (MR CLEAN). N Engl J Med. 2015;372(1):11-20. PMID: 25517348
• Nogueira RG, et al. Thrombectomy 6 to 24 hours after stroke with a mismatch between deficit and infarct (DAWN). N Engl J Med. 2018;378(1):11-21. PMID: 29129157
• Albers GW, et al. Thrombectomy for stroke at 6 to 16 hours with selection by perfusion imaging (DEFUSE 3). N Engl J Med. 2018;378(8):708-718. PMID: 29364767
• Hanley DF, et al. Efficacy and safety of minimally invasive surgery with thrombolysis in intracerebral haemorrhage evacuation (MISTIE III). Lancet. 2019;393(10175):1021-1032. PMID: 30739747
• Mendelow AD, et al. Early surgery versus initial conservative treatment in patients with spontaneous supratentorial lobar intracerebral haematomas (STICH II). Lancet. 2013;382(9890):397-408. PMID: 23726393
• Fiorella D, et al. Middle meningeal artery embolization for chronic subdural hematoma (EMBOLISE). N Engl J Med. 2024;391:568-578. PMID: 37856610

Textbooks

• Greenberg MS. Handbook of Neurosurgery. 9th ed. Thieme; 2020.
• Winn HR. Youmans and Winn Neurological Surgery. 8th ed. Elsevier; 2022.
• Rhoton AL. Rhoton's Cranial Anatomy and Surgical Approaches. Oxford University Press; 2019.
• Benzel EC. The Cervical Spine. 5th ed. Lippincott Williams & Wilkins; 2012.
• Vaccaro AR, et al. Spine Surgery: Techniques, Complication Avoidance, and Management. 4th ed. Elsevier; 2021.
• Louis DN, et al. WHO Classification of Tumours of the Central Nervous System. 5th ed. IARC; 2021.
• Brain Trauma Foundation. Guidelines for the Management of Severe Traumatic Brain Injury. 4th ed. 2016.