Ipsilateral hemiparesis and spontaneous horizontal nystagmus caused by middle cerebral artery territory infarct in a patient with agenesis of the corpus callosum.

Ipsilateral hemiparesis and spontaneous nystagmus have rarely been reported after a cerebral lesion. A 35-year-old man with agenesis of the corpus callosum developed ipsilateral hemiparesis and spontaneous horizontal nystagmus after an infarct in the right middle cerebral artery territory. Magnetic resonance imaging revealed the presence of an acute infarct in the right middle and inferior frontal gyrus, supramarginal gyrus, insular gyrus, internal capsule, head of caudate nucleus, putamen, and globus pallidus. Transcranial stimulation of the hand area of the cerebral motor cortex produced motor-evoked potentials in the abductor pollicis brevis muscle exclusively on the ipsilateral side. No motor-evoked potentials were evoked in the abductor pollicis brevis muscle contralateral to the stimulation. The motor-evoked potentials and magnetic resonance imaging findings in our case suggest that anomalies of the decussation of the corticospinal tracts can be found in agenesis of the corpus callosum.