Isolated Fourth Ventricle

An adult case of isolated fourth ventricle with an unusual clinical course is reported. A 62-yearold female had undergone lateral ventriculo-peritoneal (V-P) shunting for communicating hydrocephalus which was related to subarachnoid hemorrhage (SAH). Approximately three months later, following surgery for acute traumatic subdural hematoma (ATSDH) the symptoms of posterior fossa mass lesion developed. Computed tomography scan revealed disproportionate enlargement of the fourth ventricle, which was treated by fourth V-P shunting. Ultimately, the patient recovered well and returned to normal life. A possible mechanism for the isolated fourth ventricle in this case might be that the aqueduct was occluded by a midline shift due to ATSDH, in addition to the communicating hydrocephalus caused by SAH. The authors stress that the recognition of this entity is, indeed, important and that early diagnosis and adequate surgical intervention are indispensable.