Brain Herniation Syndromes

Snapshot

A 70-year-old man presents to the emergency department with confusion after having a convulsive episode. Prior to having a seizure, the patient reported to having a progressively worsening headache that awoke him from sleep, and right-sided weakness over the course of 7 months. On physical exam, there is weakness 2/5 strength throughout the right-side, and a left pupil that is unresponsive to light. A computerized tomography (CT) scan of the head shows a ring-enhancing lesion with surrounding cerebral edema. (Uncal herniation)

Introduction

Clinical definition
- brain tissue herniation that can result in compression of
  - brain tissue
  - vascular supply
Pathogenesis
- space occupying masses can result in mass effect (intracranial structure displacement) and they include
  - tumor
  - edema
  - hemorrhage

Herniation Syndromes

Three Clinically Important Brain Herniation Syndromes
Herniation Syndrome	Mechanism	Clinical Findings
Transtentorial herniation	The medial temporal lobe (especially, the uncus) herniatesthrough the tentorial notch	Uncal herniation triad ipsilateral unresponsive (“blown”) pupil hemiplegiatypically contralateral; however,if midbrain is compressed on the opposite side it can result inipsilateral hemiplegia (Kernohan’s phenomenon)decreased level of consciousness secondary tocompression of the midbrain reticular formation and can progress tocoma
Central herniation	The brainstem becomes downwardly and centrally dispaced	Unilateral or bilateral lacteral rectus palsy in cases ofmild central herniation that compresses theabducens nerve Bilateral uncal herniation in cases ofsignificant central herniationTonsillar herniationcerebellar tonsils herniates through the foramen magnum that can result incompression of the midbrain that leads torespiratory arrestcardiovascular instabilitydeath
Subfalcine herniation	The cingulate gyrus (as well as other structures) herniates under the falx cerebri	At times this can lead to anterior cerebral artery compression under the falx cerebri resulting ininfarction