[Unilateral ptosis induced by pure midbrain infarction: a case report].

We describe herein a case with left-side ptosis induced by pure midbrain infarction in a 49-year-old woman. She also presented with diplopia and right-side cerebellar ataxia. MRI demonstrated new ischemic stroke of the left ventral paramedian midbrain. In this case, ischemia of the left oculomotor fascicles caused the left-side ptosis and diplopia, and ischemia of the left decussation of the superior cerebellar peduncle caused the right-side cerebellar ataxia. These symptoms resulted from inner superior medial mesencephalic branch infraction. This case offers an educational example that can be explained by models proposed in the past and requires knowledge of neuroanatomy and cerebrovasculature.