Atypical Basal Ganglia germ cell tumor presenting as cerebral and brainstem hemiatrophy.

We describe a 20-year-old male patient with a germ cell tumor of the basal ganglia who presented with progressive hemiparesis and hemisensory loss. Initial computed tomography and magnetic resonance imaging showed ipsilateral cerebral and brain stem hemiatrophy predominantly in the left basal ganglia and thalamus, whereas no mass or enhancement was depicted. Single photon emission computed tomography revealed mild hypoactivity of the left cerebral hemisphere. Stereotactic biopsy was performed after a mass lesion became apparent, allowing histologic verification of germ cell tumor to be established.