1. A cerebral peduncle indentation associated with some forms of transtentorial herniation (uncal herniation). It is a secondary condition caused by a primary injury on the opposite hemisphere of the brain. Kernohan’s notch is an ipsilateral condition, in that a left-sided primary lesion (in which Kernohan’s notch would be on the right side) evokes motor impairment in the left side of the body and a right-sided primary injury evokes motor impairment in the right side of the body. The seriousness of Kernohan’s notch varies depending on the primary problem causing it, which may range from benign brain tumors to advanced subdural hematoma. (wikipedia.org)
2. A notch in the cerebral peduncle caused by displacement of the brainstem against the incisura of the tentorium by a transtentorial herniation. (biology-online.org)