Uncal herniation diagnosis [Neurosurgery Wiki]

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====== Uncal herniation diagnosis ======

The [[tentorial incisura]] surrounds the interpeduncular and pre-pontine cisterns and brainstem.

There is great interpersonal variability in the amount of space in the incisura.

===== Radiographic features =====

==== CT ====

Impending uncal or hippocampal herniation may be indicated by encroachment on the lateral aspect of the suprasellar cistern → flattening of normal pentagonal shape. Once herniation occurs CT may show: brainstem displacement and flattening compression of the contralateral cerebral peduncle, and midbrain rotation with a slight increase of ipsilateral subarachnoid space. Also, contralateral hydrocephalus may occur.

Obliteration of parasellar and interpeduncular cisterns occurs as uncus and/or hippocampus are
forced through hiatus. The brainstem is elongated in the AP direction due to lateral compression. Since dural structures enhance with IV contrast, this may be used to help delineate tentorial margins when necessary.
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{{::chronicsubduralhematomarebleedingct.jpg?266|}}{{::uncal_herniationct.jpg?300|}}

A 79-year-old patient with left [[chronic subdural hematoma]] was operated on. Marked worsening of the neurological condition, and [[drowsiness]].
A greater deformation of the [[midbrain]] and collapse of the right [[perimesencephalic cistern]] are observed, these findings being compatible with left [[uncal herniation]]


==== MRI ====


Uncal herniation can be suggested on CT, however, MRI is the gold standard. Mass effect and obliteration of the suprasellar cistern will be seen. The midbrain is displaced and effaced. 


Unilateral transtentorial herniation:

more common 
uncus and medial temporal lobe displaced medially causing effacement of the suprasellar cistern if mild
hippocampus will obliterate the quadrigeminal cistern in moderate transtentorial herniation
Bilateral transtentorial herniation:

occurs due to extensive mass effect or severe trauma, less common
both temporal lobes herniated into tentorial incisura
complete obliteration of suprasellar cistern 
midbrain effaced and displaced inferiorly
Treatment and prognosis

Uncal herniation carries a bad prognosis due to the direct compression of the vital midbrain centres. They often require emergency neurosurgical decompression.