["Cryptic" arteriovenous malformation of the brain stem--a successfully operated case (author's transl)].

We have experienced a case of a 35-year-old man with a lesion located on the left lateral surface of the floor of the 4th ventricle and showing high density on CT, part of which showed positive contrast enhancement. The patient was successfully treated by complete excision of the lesion. Pathological study indicated arteriovenous malformation.