Primary mediastinal malignant germ cell neoplasms: imaging features.

Mature teratomas are the most frequent primary mediastinal GCN. These are spherical multilocular cystic masses with thin, soft tissue septa and frequent internal fat attenuation. Primary mediastinal malignant GCNs are rare and should be included in the differential diagnosis of anterior mediastinal masses in young adult males. Seminomas are typically homogeneous masses indistinguishable from lymphomas. Radiologically nonseminomatous malignant germ cell neoplasms are large, locally invasive heterogeneous masses with central low-attenuation and frond-like peripheral soft tissue. Gonadal primary malignancy and intervening abdominal lymph node involvement should be excluded. Tumor markers play a crucial role in the initial evaluation of anterior mediastinal masses in these patients and in evaluating response to therapy and possible recurrence. Follow-up imaging is helpful in detection and characterization of residual neoplasm.