[Case of ipsilateral monoparesis by lacunar infarction: a consideration on the pathological mechanism].

An 81-year-old man had sudden-onset dysarthria and weakness in the right leg, and was admitted to our hospital in July 2009. Neurological examination showed right leg monoparesis, sensory disturbance on the right limbs, dysarthria, and decreased deep tendon reflexes. Brain MRI revealed an acute lacunar infarction in the right corona radiata and an old lacunar infarction in the left centrum semiovale, which occurred 4 years before. MR tractography disclosed impaired motor fibers in the right corona radiata, and transcranial magnetic stimulation (TMS) suggested diminished innervation from the bilateral cerebral cortices to the right leg. These results collectively indicated that reorganization of the pyramidal fibers were responsible for the monoparesis ipsilateral to the lacunar infarction, although anomalous pyramidal fibers with ipsilateral innervation were responsible for ipsilateral hemiplegia a previous study.