[A case of pineal teratoma arising from hydrocephalus of unknown cause].

We report a case of "functional aqueductal stenosis" which reveals dilatation of the lateral and 3rd ventricles without stenosis at the aqueduct in MRI. This case shows a pineal teratoma which presents one year later with symptoms of hydrocephalus caused by "functional aqueductal stenosis". A seven-year-old boy was admitted to our department owing to headache and vomiting. CT and MRI showed hydrocephalus. The lateral and 3rd ventricles were dilated while the 4th ventricle was normal. Furthermore, tumoral obstruction of the aqueduct was not found. After a ventriculoperitoneal shunt, he recovered well without neurological deficits. One year later, symptoms of precocious puberty, that is the appearance of public hair and deepening of his voice, were found. A follow-up MRI demonstrated a pineal region tumor. Although human chorionic gonadotropin level in the serum and urine was transiently elevated, it normalized before surgery. The operation was performed by the occipital transtentorial approach and the tumor was totally removed. Histological examination proved this tumor to be a mature teratoma, showing three germ cell layers. About two weeks later, he was discharged without any neurological deficit. In this case, although hydrocephalus occurred, MRI didn't demonstrate aqueductal obstruction caused by the tumor. However, one year later, a pineal region tumor was confirmed by MRI. This suggests that hydrocephalus might have some association with the appearance of the pineal region tumor. Therefore, it is necessary to be aware of the possibility of the occurrence of tumors whenever we encounter "functional aqueductal obstruction", when MRI doesn't demonstrate aqueductal obstruction caused by a tumor.