Diagnosis of descending transtentorial herniation by cranial computed tomography.

Descending transtentorial herniartion (DTH) secondary to a supratentorial mass effect can be detected by CT. Early signs of uncal herniation include encroachment on the suprasellar cistern, displacement of the brain stem, enlargement of the ipsilateral crural subarachnoid space, and compression of the contralateral cerebral peduncle. Increasingly severe combined uncal and hippocampal DTH results in progressive obliteration of the suprasellar and interpeduncular cisterns, elongation or compression of the brain stem, and inferior or posterior displacement of the basilar artery.