Ectopic Germinoma: A Delayed Diagnosis With Serial Magnetic Resonance Imaging Features

Germinoma arising from intracranial off-midline structures is considered ectopic. Although basal ganglia germinoma is a rare occurrence, it is more commonly seen in the Asian population, particularly among boys. Here, we report a case of an adolescent boy who presented with hemiplegia and delayed diagnosis of basal ganglia germinoma with progression on serial magnetic resonance imaging (MRI). Several signal changes have been described during the early stage of the disease such as T2-weighted patchy hyperintense signal, cerebral hemiatrophy, and signal change on susceptibility-weighted imaging. ¹¹C-methionine positron emission tomography is an additional imaging technique that can reveal ectopic germinoma. Follow-up MRI revealed small cystic changes, and the latest imaging showed progression into a large multicystic lesion with mass effect. The patient underwent surgery, and histopathological examination revealed basal ganglia germinoma. We highlight the serial MRI changes that were suggestive of basal ganglia germinoma in this case.