Transtentorial Herniation

Explanation:
This 26 year-old female presented with a 2 week history of headache and nausea. Previous investigations had included a CT and MRI, reported to be normal, and a lumbar puncture with an opening pressure of 40cm H2O and a monocytosis.
Treatment for viral meningitis was instituted. The patient deteriorated, with vomiting, systemic hypertension (160/120), headache, 4th cranial nerve palsies, visual disturbance and papilloedema.
The CT demonstrates effacement of the quadrigeminal plate and ambient cisterns consistent with transtentorial herniation. There is also loss of the grey-white differentiation, and effacement of the surface subarachnoid spaces, consistent with cerebral oedema.
Cranial nerve palsies may occur with transtentorial herniation. The fourth cranial nerve has a long, exposed course after its exit from the dorsal midbrain, and is prone to compression against the tentorium cerebelli. Cranial nerve nuclei may also be damaged by compression of the brainstem, usually causing multiple cranial nerve deficits.
Another possible complication of transtentorial herniation is infarction of the posterior cerebral artery territory as the artery is compressed against the tentorial incisura. The midbrain and basal ganglia may also infarct due to occlusion of perforators arising from the Circle of Willis.
Reference: Anne Osborn. Diagnostic Neuroradiology. Mosby 1994
Credit: Dr Laughlin Dawes
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