[A case of abulia without memory disturbance due to infarction of the bilateral genua of the internal capsules].

A 68-year-old right handed man with treated hypertension presented with acute-onset somnolence without hemiparesis, dysarthria or sensory disturbance. Although he became laconic and his verbal responses were only in short terms, his replies were accurate and judgmental. A cranial MRI in axial, coronal, and sagittal section revealed small hemorrhagic infarcts essentially limited to the bilateral capsular genua without involvement of the inferior thalamic peduncles. A 123I-IMP single photon emission CT disclosed remarkable hypoperfusion in the bilateral frontal cortex. After a week of somnolence, he gradually became wakeful, but was still abulic. Neuropsychological examinations revealed no memory disturbance. We consider that disconnection of the thalamo-frontal projection at the genua of the internal capsules caused somnolence, apathy, and abulia in our case. The hitherto reported cases of the genu infarcts that showed memory disturbance had the lesion involving both the inferior thalamic peduncle and its nearby mamillothalamic tract. In contrast, our case without memory disturbance had infarcts confined to the genua apparently sparing the two tracts, implicating that memory function may be preserved when such structures are intact.