Germ-Cell and Other Bad Tumors

Germinoma is the most frequent intracranial germ-cell tumor. It arises along the midline from the pituitary stalk or the pineal gland or from both. There is a peak frequency in early puberty, mainly in boys. A polyuro-polydipsic syndrome is usually the first manifestation. The vasopressin bright spot is missing on axial T1WI. The thickening of the pituitary stalk may be equivocal and it is highly recommended to repeat the MRI quickly if the first examination is negative. Later on, the germ-cell tumor appears as a well-delineated round or lobulated suprasellar mass without any specific T1 or T2W signal. Non-germinomatous germ cell tumors present usually as posterior third ventricular masses with hydrocephalus and midbrain compression. This group includes teratomas and choriocarcinomas. Pilocytic astrocytomas can mimic adamantinous craniopharyngiomas. The “cut green pepper sign” could help to differentiate them.