Rhabdomyosarcoma of the brain.

The authors report a case of rhabdomyosarcoma originating in the fourth ventricle and review the eight comparable previous reports on true rhabdomyosarcoma, composed solely of mesenchymal elements. Tumors in most adults arose in the cerebral hemisphere, while those in children arose exclusively in the midline structures of the posterior fossa. The tumor in the author's case was initially benign and well circumscribed, but within 2 years had changed into a malignant rhabdomyosarcoma. The histological documentation during the interval is presented and discussed.