Basal ganglia germinoma in children with associated ipsilateral cerebral and brain stem hemiatrophy

Germinoma is the most common and least-malignant intracranial germ cell tumor, usually found in the midline. Germinoma that arises in the basal ganglia, called ectopic germinoma, is a rare and well-documented entity representing 5% to 10% of all intracranial germinomas. The association of cerebral and/or brain stem atrophy with basal ganglia germinoma on CT and MRI is found in 33% of the cases.

To review the literature and describe the CT and MRI findings of basal ganglia germinoma in children, known as ectopic germinoma, with associated ipsilateral cerebral and brain stem hemiatrophy.

Three brain CT and six brain MRI studies performed in four children at two institutions were retrospectively reviewed. All patients were male (case 1, 14 years; case 2, 13 years; case 3, 9 years; case 4, 13 years), with pathologically proved germinoma arising in the basal ganglia, and associated ipsilateral cerebral and/or brain stem hemiatrophy on the first imaging study. It is important to note that three of these children presented with cognitive decline, psychosis and slowly progressive hemiparesis as their indication for imaging.

Imaging results on initial scans were varied. In all patients, the initial study showed ipsilateral cerebral and/or brain stem hemiatrophy, representing Wallerian degeneration. All patients who underwent CT imaging presented with a hyperdense or calcified lesion in the basal ganglia on unenhanced scans. Only one of these lesions had a mass effect on the surrounding structures. In one of these patients a large, complex, heterogeneous mass appeared 15 months later. Initial MR showed focal or diffusely increased T2 signal in two cases and heterogeneous signal in the other two.

The association of a focal lesion in the basal ganglia of children with progressive hemiparesis, neuropsychiatric symptoms and ipsilateral cerebral and/or brain stem hemiatrophy should prompt the diagnosis of ectopic germinoma, avoiding delay in the diagnosis and further irreversible clinical deterioration, in a malignancy with an otherwise favorable prognosis. In these patients, hemiatrophy preceding or accompanying the imaging depiction of a basal ganglia mass lesion is thought to be caused by a paraneoplastic process.