What are the types of brain herniation?

Types of Brain Herniation

Brain herniation is classified into intracranial and extracranial types, with intracranial hernias further divided into subfalcine, transtentorial (ascending or descending), and tonsillar herniation. 1

Intracranial Herniation Types

Subfalcine Herniation

• Most common type of brain herniation, occurring when brain tissue shifts beneath the falx cerebri across the midline 1, 2
• In patients with intracerebral hemorrhage, subfalcine herniation was the most frequently observed pattern (found in 6 of 11 patients with herniation) 2
• Generally well-tolerated unless lateral displacement becomes excessive 3
• Associated with compression of the anterior cerebral artery and potential infarction in its territory 4

Transtentorial Herniation

This category includes two distinct subtypes based on direction of herniation:

Descending Transtentorial Herniation

• Uncal herniation: Occurs when the medial temporal lobe (uncus) herniates through the tentorial opening 4, 1

• In intracerebral hemorrhage patients, uncal herniation was the second most common pattern (found in 3 of 11 patients with herniation) 2

• Contrary to traditional teaching, temporal lobe herniation may not be the primary mechanism of irreversible midbrain damage; rather, lateral displacement of the brain at the tentorium appears to be the critical factor 3

• Can cause compression of the third cranial nerve, leading to ipsilateral pupillary dilation and fixed pupil 4

• Central transtentorial herniation: Downward displacement of both cerebral hemispheres and basal ganglia through the tentorial opening 1

Ascending Transtentorial Herniation

• Upward cerebellar herniation: Occurs when posterior fossa contents herniate upward through the tentorial opening 4, 1
• Primarily serves as a sign of an overfull posterior fossa rather than a primary pathologic mechanism 3
• Can result from space-occupying cerebellar strokes, leading to brainstem compression with transtentorial (upward) herniation 4

Tonsillar Herniation

• Downward herniation of cerebellar tonsils through the foramen magnum 1
• Also termed "transforaminal herniation" or "cerebellar pressure coning" 4
• In space-occupying cerebellar strokes, can lead to death from transforaminal (downward) herniation 4
• Historical observations have raised questions about its universally lethal reputation, though it remains a critical complication 3

Combined Herniation Patterns

• Multiple simultaneous herniations are common: In one series, combined subfalcine and uncal herniation occurred in one patient, while another demonstrated subfalcine, uncal, and tonsillar herniation simultaneously 2
• The imaging spectrum shows that many herniation patterns overlap, and it is essential to recognize that patients may exhibit features of multiple herniation types concurrently 1, 5

Clinical Correlates and Imaging

• Each herniation type produces specific neurologic syndromes based on the structures compressed 1
• Herniation can cause brain damage through multiple mechanisms: compression of cranial nerves and vessels (causing hemorrhage or ischemia), obstruction of cerebrospinal fluid circulation (producing hydrocephalus), and direct tissue compression 1
• CT is the preferred imaging modality due to shorter acquisition time, lower cost, and wider availability, though MRI provides superior soft tissue visualization 1, 5
• Radiologic signs include midline shift, compression of basal cisterns, ventricular compression, and displacement of specific brain structures depending on herniation type 4, 1