Cerebral Edema & Herniation Syndromes

ABPN Neurocritical Care Study Guide Exam

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1 Chapter 1: Neurologic Examination & Coma Assessment in the ICU

Current Examination, Blueprint & Preparation Neurologic Examination in Critically Ill Patients Coma Evaluation & Consciousness Alterations Delirium & Toxic-Metabolic Encephalopathy in the ICU

2 Chapter 2: Cerebral Physiology & Intracranial Dynamics

Cerebral Blood Flow, Metabolism & Autoregulation Intracranial Pressure & Compliance Cerebral Edema & Herniation Syndromes

3 Chapter 3: Intracranial Hypertension & Cerebral Perfusion Management

Tiered ICP Management Protocols Hyperosmolar Therapy & Fluid Management Advanced & Refractory ICP Interventions

4 Chapter 4: Airway, Mechanical Ventilation & Pulmonary ICU Management

Emergency Airway Management & Neuro-Intubation Mechanical Ventilation Strategies in Acute Brain Injury Tracheostomy & Ventilator Weaning in Neurocritical Care Pulmonary Complications in the Neuro-ICU Obstructive Lung Disease, Pulmonary Hypertension & Bronchoscopy

5 Chapter 5: Hemodynamics, Shock & Cardiovascular Management

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6 Chapter 6: Neuropharmacology, Analgesia & Sedation

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7 Bleeding, Thrombosis & Hematologic Emergencies

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8 Chapter 8: Systemic ICU Care, Fluids, Electrolytes & Endocrine

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10 Cardiac Emergencies & Mechanical Support

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14 Chapter 9: Neuroimaging in the Neuro-ICU

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15 Chapter 10: Electrophysiology & Neuromonitoring

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16 Angiography, Electrodiagnosis & CSF Analysis

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17 Chapter 11: Bedside Procedures, Ultrasound & Death by Neurologic Criteria

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18 Chapter 12: Acute Ischemic Stroke & Reperfusion Therapies

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19 Chapter 13: Spontaneous Intracerebral Hemorrhage & Intraventricular Hemorrhage

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20 Chapter 14: Aneurysmal Subarachnoid Hemorrhage & Delayed Cerebral Ischemia

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21 Venous, Spinal & Traumatic Vascular Disease

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22 Chapter 15: Traumatic Brain & Spinal Cord Injury

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23 Chapter 16: Status Epilepticus, Seizures & Neuromuscular Emergencies

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24 Chapter 17: Post-Cardiac Arrest Care, CNS Infections & Encephalitis

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25 Neuroinflammation & Neurooncology

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26 Pregnancy, Transplantation & Pediatric Care

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27 Chapter 18: Neurosurgical & Perioperative Emergencies

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28 Chapter 19: Ethics, Palliative Care & Organ Donation in the Neuro-ICU

Communication, Surrogate Decision-Making & Conflict Resolution Neuroprognostication Ethics, Withdrawal of Life Support & Palliative Care Organ Donation & Management of the Deceased Donor

Cerebral Edema & Herniation Syndromes

Key Takeaways Explain This Topic AI

Do not use corticosteroids to treat TBI edema or improve TBI outcome; CRASH found increased mortality with high-dose methylprednisolone.

Uncal herniation classically produces ipsilateral pupillary dilation from superficial parasympathetic Cranial Nerve III compression and contralateral hemiparesis; Kernohan's notch phenomenon produces paradoxical ipsilateral hemiparesis.

Central herniation follows a stereotypical rostrocaudal progression from diencephalic small reactive pupils to midbrain fixed mid-position pupils and decerebrate posturing.

Subfalcine herniation causes anterior cerebral artery compression, tonsillar herniation compresses the medulla causing Cushing's triad and apnea, and upward herniation causes upward gaze impairment.

Last updated: October 2026

2.3 Cerebral Edema & Herniation Syndromes

Cerebral edema is an abnormal accumulation of fluid within brain parenchyma resulting in volumetric expansion. When tissue expansion exceeds spatial compensatory reserve, pressure gradients develop across rigid dural partitions—the falx cerebri, tentorium cerebelli, and foramen magnum. The resulting mechanical displacement compresses vital neurovascular pathways, culminating in stereotypical herniation syndromes.

Pathophysiologic Subtypes of Cerebral Edema

Cerebral edema is categorized into four distinct pathophysiologic classes:

Edema Type Location BBB Integrity Fluid Compartment Etiologies Steroid Responsive? First-Line Management

Vasogenic White matter Disrupted (tight junctions open) Extracellular (plasma proteins) Neoplasms, abscess, radionecrosis Cause-dependent Tumor steroids when indicated; infection/source control for abscess, with steroids only for selected severe edema

Cytotoxic Gray and white matter Intact (early phases) Intracellular (cell swelling) Ischemic stroke, arrest anoxia, TBI No (contraindicated in TBI) Osmotherapy, hemicraniectomy

Interstitial Periventricular white matter Intact Extracellular (CSF transudate) Acute hydrocephalus No CSF diversion (EVD, shunt)

Osmotic Diffuse gray & white matter Intact Intracellular (osmotic shift) Acute hyponatremia, rapid lowering of chronic hypernatremia, selected metabolic emergencies No Controlled sodium titration

1. Vasogenic Edema

Vasogenic edema stems from breakdown of blood-brain barrier (BBB) tight junctions (claudin-5, occludin, ZO-1) driven by VEGF and inflammatory cytokines. Plasma proteins and fluid extravasate into extracellular spaces, tracking through subcortical white matter along parallel axonal tracts that offer minimal mechanical resistance, sparing cortical gray matter. Neoplastic vasogenic edema responds dramatically to dexamethasone ( 4 – 10 mg 4\text{--}10\text{ mg} 4 – 10 mg IV q6h), which stabilizes tight junctions and downregulates VEGF.

Caution

The MRC CRASH trial demonstrated that high-dose corticosteroids in traumatic brain injury significantly increase mortality. Steroids should not be used to treat TBI-related edema or improve TBI outcome; a separate indication requires its own assessment and provide no benefit in acute ischemic stroke or intracerebral hemorrhage.

2. Cytotoxic (Cellular) Edema

Cytotoxic edema results from cellular energy failure. Depletion of ATP halts Na + / K + \text{Na}^+/\text{K}^+ Na + / K + -ATPase pumps, causing intracellular Na + \text{Na}^+ Na + accumulation and osmotic swelling of neurons and astrocytes. Astrocytic water entry is mediated by aquaporin-4 (AQP4) channels. Involving both gray and white matter, it produces sulcal effacement and loss of gray-white differentiation on CT. It is unresponsive to corticosteroids, requiring osmotherapy (mannitol, hypertonic saline) and decompressive surgery.

3. Interstitial and Osmotic Edema

Interstitial (Hydrocephalic) Edema: Elevated intraventricular pressure in acute hydrocephalus forces CSF across the ventricular ependymal lining into periventricular white matter (trans-ependymal transudation), seen as a periventricular halo on CT/FLAIR. Definitive therapy is CSF diversion via EVD.

Osmotic Edema: Acute drops in serum osmolality create a trans-barrier gradient driving water into parenchymal cells. Etiologies include rapid correction of hypernatremia, acute hyponatremia, and water intoxication.

Mechanical Brain Herniation Syndromes

When localized edema or mass lesions generate compartmental pressure gradients, parenchyma shifts across internal dural folds or through the foramen magnum:

Herniation Syndrome Displaced Structure Compressive Pathology Cardinal Clinical Signs

Uncal (Lateral Transtentorial) Medial temporal uncus over tentorium Ipsilateral CN III, cerebral peduncle, PCA Ipsilateral blown pupil, contralateral hemiparesis (or ipsilateral via Kernohan's notch), PCA stroke

Central (Transtentorial) Bilateral hemispheres & diencephalon downward Basilar perforators, midbrain, pons Rostrocaudal progression: small reactive pupils → \rightarrow → fixed mid-position pupils, decorticate → \rightarrow → decerebrate

Subfalcine (Cingulate) Cingulate gyrus beneath falx cerebri Anterior cerebral arteries, foramen of Monro Contralateral leg-predominant hemiparesis, abulia, trapped hydrocephalus

Tonsillar Cerebellar tonsils through foramen magnum Medulla oblongata, cervicomedullary junction Cushing's triad (hypertension, bradycardia, irregular breathing), rapid apnea, arrest

Upward Transtentorial Superior cerebellar vermis upward Dorsal midbrain tectum, superior cerebellar arteries Downward gaze palsy, stupor, mid-position fixed pupils, hydrocephalus

Transcalvarial (External) Cortical parenchyma through skull defect Cortical bridging veins against bone edges Venous congestion, hemorrhagic venous infarction, external venous congestion; syndrome of the trephined is a separate complication of the skull defect

1. Uncal (Lateral Transtentorial) Herniation

Uncal herniation occurs when an expanding supratentorial mass forces the medial temporal uncus over the tentorium cerebelli into the posterior fossa:

CN III Compression: Parasympathetic pupillomotor fibers travel on the superficial dorsomedial perimeter of CN III. Extrinsic compression produces ipsilateral pupillary sluggishness progressing rapidly to mydriasis and light unresponsiveness ("blown pupil") . Deeper somatic motor fibers fail later, causing ptosis and ophthalmoplegia.

Cerebral Peduncle Compression: Compression of the ipsilateral cerebral peduncle produces contralateral hemiparesis .

Kernohan's Notch Phenomenon (False-Localizing Sign): Severe lateral midbrain shift crushes the contralateral cerebral peduncle against the opposite tentorial edge (Kernohan's notch), causing motor weakness ipsilateral to the mass lesion . The ipsilateral dilated pupil correctly localizes the lesion side.

Vascular Sequelae: PCA compression causes occipital infarction. Downward basilar artery traction tears paramedian perforators, causing fatal Duret hemorrhages in the midbrain and pons.

2. Central (Transtentorial) Herniation

Central herniation involves symmetric downward displacement of hemispheres and diencephalon through the incisura, manifesting as rostrocaudal deterioration:

Diencephalic Stage: Stupor, small reactive pupils ("diencephalic pupils"), Cheyne-Stokes breathing, and decorticate (flexor) posturing.

Midbrain-Upper Pons Stage: Deep coma, fixed mid-position pupils (3–5 mm), loss of oculocephalic reflexes, central neurogenic hyperventilation, and decerebrate (extensor) posturing.

Medullary Stage: Flaccid quadriplegia, ataxic breathing, and terminal cardiopulmonary arrest.

3. Subfalcine, Tonsillar, and Other Syndromes

Subfalcine Herniation: The cingulate gyrus shifts beneath the falx cerebri, compressing anterior cerebral artery (ACA) branches to cause contralateral leg-predominant weakness , abulia, and trapped hydrocephalus from foramen of Monro occlusion.

Tonsillar Herniation: Cerebellar tonsils are forced through the foramen magnum, crushing the medulla. This triggers Cushing's triad (hypertension with widened pulse pressure, bradycardia, irregular breathing) followed by sudden apnea and arrest.

Upward Transtentorial Herniation: Posterior fossa masses drive the vermis upward through the incisura, compressing the tectal plate to cause upward gaze impairment, fixed pupils, and hydrocephalus.

Transcalvarial Herniation: Brain tissue extrudes through a craniectomy defect. Bone edge pressure strangulates cortical veins, causing hemorrhagic venous infarction.

Important

Cushing's triad is a pre-terminal indicator of impending medullary strangulation. Its emergence demands immediate osmotherapy, hyperventilation, and emergency surgical decompression to avert fatal respiratory arrest.