Germ cell tumors of the mediastinum.

The anterior mediastinum is the most common primary extragonadal site for germinal neoplasms in adults and is second to the sacrococcygeal region for pathologially comparable tumors in children. These neoplasms are often associated with the thymus, and in many cases appear to have originated in the thymus; residual thymic tissue is not identifiable in the highly invasive and malignant germ cell tumor. Regardless of the pathologic subtype, the mediastinal germ cell tumors have a predilection for patients in the first three decades of life. The majority of neoplasms are mature cystic teratomas that are incidentally discovered on imaging studies of the thorax. Respiratory difficulties and/or chest pain are the most frequent symptoms. Among the malignant germ cell tumors, males are affected far more commonly than females, but the male to female ratio is approximately equal among mature cystic teratomas. Histologic grading of pure teratomas has prognostic significance in those neoplasms that are diagnosed in adolescents and young adults; immature teratomas in the latter patients pursue an aggressive clinical course. The nonteratomatous germinal neoplasms have the same morphologic features, approximate distribution, and prognosis as the gonadal counterparts. Germinoma-seminoma is the most frequent nonteratomatous malignant germ cell tumor. It should be remembered that mediastinal lymph nodes are metastatic sites for primary gonadal germ cell tumors, so that a thorough clinical evaluation is necessary to exclude the latter possibility.