Descending tentorial herniation (DTH) can be diagnosed by computed tomography. Encroachment upon the lateral aspect of the suprasellar cistern is an early sign of impending tentorial herniation. Actual herniation is evidenced by rotation and shift of the brain stem with consequent widening of the crural and ambient cisterns on the side of the space-occupying lesion. In a more advanced stage of herniation, obliteration of cisternal spaces at the tentorial level will occur. Aqueductal compression secondary to the herniation will cause increased intraventricular pressure with widening of those parts of the lateral ventricles that are not exposed to the compression by the mass; a characteristic finding is widening of the temporal horn on the side opposite the space-occupying lesion. Infarction in the territory of the posterior cerebral artery may complicate DTH.