[Dermoid tumor in left cerebellum--A case report (author's transl)].

This paper describes a dermoid tumor which developed in the dorso-lateral area of the left cerebellar hemisphere. It is the first to be reported in Japan. The patient was a 31 year old female who suffered from severe occipital headaches, frequent vomiting and gait disturbances. Neurological findings on admission included marked bilateral choked discs, horizontal nystagmus on gaze to the left, and poor coordination on the finger to nose test, nose-finger-nose test and and heel-shin test on the left side. Left suboccipital craniectomy was performed. A tumor was found which displaced the left cerebellum anteromedially and inferiorly. The postero-lateral surface of the tumor was adherent to the overlying dura matter. It was completely removed and found to be about the size of a hen's egg. It contained a yellow, porridge-like substance and short hairs. Histological examination of the capsule of the tumor showed stratified squamous epithelium and cutaneous structures, such as hair follicles and sebaceous glands. The diagnosis was dermoid tumors. We could find as many as 78 cases of the posterior fossa dermoids in the literature. In 72 cases (92.4%), the mass existed along the midline in the posterior fossa. The dermoids developed in the cerebellar hemisphere were reported in only 6 cases (7.6%) including the present case. Laterally growing dermoids are considered to be very rare. The pathogenesis is discussed and the literature reviewed.