Mixed germ cell tumour of the mediastinum (seminoma, embryonal carcinoma, choriocarcinoma and teratoma). Light and electron microscopic cytology and histological investigation.

A mixed germ cell tumour of the mediastinum was found in a 27-year-old subject. It had four components: seminoma, embryonal carcinoma, choriocarcinoma and teratoma. Material for light microscopy (L.M.) and ultrastructural studies were obtained with computerized tomography (CT) guided fine needle aspiration. Three histotypes were identified with ultrastructural studies while only seminoma was identified with L.M. The slides prepared for L.M. were reexamined in the light of findings with electron microscopy (E.M.) and previously unidentified cellular elements were found to be characteristic of choriocarcinoma and teratoma. Histological examination of surgical and autopsy material confirmed the cytological findings. Because of the singularity of this case, the rarity of this type of neoplasm and the difficulty in arriving at a differential diagnosis from other neoplastic and non neoplastic lesions, only the ultrastructural cytological examination allowed us to identify the mixed nature of the tumour. Such an identification is not always possible with L.M. but it is a determining factor in the prognosis and therapy.