Walsh & Hoyt: Pyramidal Signs

Pyramidal false localizing signs were present in 26 of the cases reviewed by Gassel. In 15 patients, they were bilateral despite a unilateral, supratentorial tumor. In nine patients, they were ipsilateral, and in two patients, they were contralateral. We have also observed supratentorial tumors that produced signs of pyramidal tract disturbance that were both ipsilateral and contralateral to the tumor. In the latter setting, damage to the contralateral cerebral peduncle is caused by a shift of the brain stem, resulting in indentation of the peduncle by the edge of the tentorium (the Kernohan notch phenomenon).