Germinoma presenting as a fourth cranial nerve palsy in a patient with adenomatous polyposis coli (APC) gene mutation.

A 17-year-old boy with adenomatous polyposis and a history of an adenomatous polyposis coli (APC) gene mutation (IVS13(-2) A>G) presented for evaluation of vertical, binocular diplopia. Examination was suggestive of a fourth (trochlear) nerve palsy. A history of headaches was elicited and led to further investigation with neuroimaging, which identified a germinoma in the tectal plate and secondary hydrocephalus. We report the clinical, radiological, and histopathological findings of this patient, who to our knowledge is the first reported case of a germinoma occurring in association with adenomatous polyposis.