Kernohan-Woltman notch phenomenon caused by an acute subdural hematoma.

Uncal herniation through the tentorial notch is occasionally associated with false localizing ipsilateral hemiparesis, known as the Kernohan-Woltman notch phenomenon (KWNP). We report an 81-year-old female who presented with a decreased level of consciousness, a right mydriasis and an ipsilateral motor deficit caused by a large right hemispheric subdural hematoma that was immediately evacuated. The patient recovered well, although her right hemiplegia persisted. A follow-up MRI showed a residual lesion in the left cerebral peduncle, corresponding to KWNP. The presence of such a structural lesion suggests a poor prognosis for recovery from the initial motor deficit.