Right uncal herniation: Uncal herniation is most commonly unilateral and is observed with unilateral lesions involving one of the cerebral hemispheres. However, it may be seen with bilateral swelling of the hemispheres, in which case the herniation is bilateral. This view of the inferior aspect of the brain shows herniation of the uncus on the left side of the photograph (right side of the brain), which means that a lesion in this hemisphere has created enough pressure to force the medial part of the temporal lobe over the free edge of the tentorium. The groove created by the edge of the tentorium is readily identified. (Compare the uncus on the two sides and note the asymmetry.) Note also that the brain stem is deviated away from the right cerebral hemisphere.