CT and MRI features of intracranial germ cell tumors.

The computed tomographic (CT) and magnetic resonance imaging (MRI) features of 73 histologically proven primary intracranial germ cell tumors were analysed. CT images were available for all 73 patients, and 22 of them were also examined by MRI. The tumors were classified as germinoma, mature teratoma, immature or malignant teratoma, yolk sac tumor, choriocarcinoma, embryonal carcinoma and mixed type. Germinoma was revealed as a high- or slightly high-density area on plain CT scan, and was enhanced homogeneously. MRI revealed iso- or slightly low signal intensity on T1-weighted images, and iso- or high intensity on T2-weighted images. Mature teratoma, which had a clear margin on neuroradiological images, was characterized by mixed density on CT scans, often showing large cysts and area of calcification. Immature or malignant teratoma had a similar pattern to that of mature teratoma, but the cystic components and area of calcification tended to be less and smaller respectively. The tumor margin was obscure in malignant teratoma, and perifocal edema was observed in some cases. The shape of yolk sac tumors was irregular. Plain CT scan revealed an iso- or low-density mass with good heterogeneous enhancement. Perifocal edema was observed in some cases. In mixed germ cell tumors, MRI imaging was useful for detecting teratomatous components, particularly fatty components. Although definite histological diagnosis cannot be achieved by CT and/or MRI alone, detailed analysis of neuroradiological images are useful for predicting the histological diagnosis.