Fine needle aspiration cytology of primary mediastinal germ cell tumors.

Fine needle aspiration cytology was performed on six patients with malignant mediastinal germ cell tumor: 1 pure seminoma, 1 pure embryonal carcinoma, 1 pure yolk sac tumor and 3 mixed germ cell tumors containing teratoma. Their cytologic features were compared with each other and with the cytologic features of thymoma, which arises commonly in the anterior mediastinum. A definitive cytologic diagnosis could be made only in the cases of seminoma because of its characteristic cytologic features. Cytochemical staining for germ cell alkaline phosphatase was helpful in diagnosing seminoma in the cytologic examination, while the presence of hyaline globule or alpha-fetoprotein immunostaining as the cytologic diagnostic feature of yolk sac tumor were not necessarily found in fine needle aspiration cytology. All epithelial, lymphocytic and mixed type thymomas were easily differentiated from the four types of germ cell tumor examined.