[One and a half syndrome and MRI--a case report and functional neuroanatomy of the syndrome].

This is a case report of 63 year old men who presented one and a half syndrome with ipsilateral peripheral type facial palsy due to lacunar infarct. MRI taken one week after the onset (TR 2000, TE 38) demonstrated small high intensity lesion, 4 mm in diameter, located at the dorsal portion of pontine tegmentum, contacting with the floor of 4th ventricle. This MRI coincides with the lesion limited to the abducens nucleus and genu of facial nerve. Traditionally, projections from the PPRF to the ipsilateral abducens nucleus and opposite MLF was postulated. Recently, however, experiment on monkey and autopsy cases showed projection from abducens nucleus, instead of PPRF, to the opposite MLF has been proposed. MRI findings in this case support the latter hypothesis. It is expected that, with the advent of MRI, more meticulous functional neuroanatomy will be developed.