[One-and-a-half syndrome due to a brain tumor--a case report and review of the literature].

A 69-year-old woman was admitted to our hospital on March 13, 1990, with a 1-month history of progressive gait disturbance. She had been operated on for colon cancer in May 1987. Examination in March 1989 revealed that she had metastatic liver tumor. On neurological examination, slight right abducens palsy, gaze-evoked horizontal nystagmus to the left, upbeat nystagmus and mild left hemiparesis were noted. Two weeks after admission, right lateral gaze palsy developed. Right MLF syndrome became apparent in the 3rd week. She was diagnosed as having one-and-a-half syndrome. Left hemi-hypesthesia and left limb ataxia were noted at that time. CT scan revealed ring-enhancing mass lesions in and around the right pontine tegmentum. Two weeks after development of the one-and-a-half syndrome, she became comatose with her eyes' conjugate deviation to the left and died on April 24, 1990. The metastatic lesions in both paramedian pontine reticular formation and medial longitudinal fasciculus were considered to be causative of her one-and-a-half syndrome. Clinical characteristics of 13 reported cases with one-and-a-half syndrome caused by brain tumor were reviewed. Half of them were caused by metastatic brain tumor.