Electron microscopy of fine‐needle aspiration biopsy from extragonadal germ cell tumors

We describe five cases of extragonadal germ cell tumor (EGCT) diagnosed by the electron microscope (EM) on cytological material. The clinical diagnosis was incorrect in all cases and EGCT was suspected in two cases; cytological diagnosis by light microscopy confirmed the presence of malignant tumor cells, but did not identify the cytotype/s correctly except in one case. Ultrasonography, laparoscopy, and autopsy (in case 3) excluded a primitive germ cell tumor (GCT). Histology confirmed the EM diagnosis in all cases. EM, even of scanty or necrotic cytological material, is particularly useful for mediastinal and retroperitoneal masses. In case of EGCT, EM can identify the different cytotypes and the different ultrastructural subcellular cytotypes and demonstrates a close relation between seminomatous and nonseminomatous GCT, which could influence their classification and prognosis.