Fine-needle aspiration cytology of unusual germ cell tumors of the mediastinum: atypical seminoma and parietal yolk sac tumor.

A 30-yr-old man presented with a mediastinal germ cell tumor that combined the histologic pattern of seminoma with the immunohistochemical profile of embryonal carcinoma (beta-HCG+/PLAP-). In FNA smears, this atypical seminoma presented as fragile large cells with scanty cytoplasm, vesicular nuclei, irregular and indistinct nucleoli, scattered singly and in loosely cohesive fragments without the characteristic lymphocytic or tigroid background. The cytologic features were more suggestive of a poorly differentiated carcinoma than seminoma, potentially leading to misdiagnosis and mismanagement. The second case was a 51-yr-old female smoker who presented with mediastinal parietal yolk sac tumor with extension to the lung, a rare occurrence, and contrary to the clinical impression of lung cancer with hilar lymph node metastasis. This case illustrates the value of using the unique cytologic features of parietal yolk sac tumor, i.e., the abundant, viscous, stringy metachromatic extracellular hyaline material associated with the tumor cells in reaching the accurate diagnosis.