ADENOMATOID TUMORS OF THE PLEURA

We report two cases of small pleural nodules showing the distinctive h istologic appearance of adenomatoid tumor. Both lesions were discovere d incidentally during surgery in patients undergoing lung resection fo r unrelated intrapulmonary masses: lung carcinoma in one case and hist oplasmosis in the other, The tumors were composed of a focal prolifera tion of epithelioid cells forming vacuoles and tubular spaces in a fib rous stroma, as seen in adenomatoid tumors from other sites. The diffe rential diagnosis in both cases included metastatic sienet ring cell c arcinoma, The mesothelial nature of the lesions was supported by immun ohistochemical and ultrastructural evidence. The tumor cells in both c ases were positive for cytokeratin but negative for carcinoembryonic a ntigen and LeuM1. One case was also negative for BER-EP4, B72.3, CD34, and Factor VIII, Electron microscopy in this case demonstrated well-d eveloped basal laminae, desmosomes, and numerous slender microvilli al ong the luminal surfaces of the tumor cells. Adenomatoid tumors are re garded as a benign variant of mesothelioma, Despite the abundance of m esothelial cells in the pleura, adenomatoid tumors are apparently extr emely rare in this location. Separation from malignant lesions such as adenocarcinoma and epithelioid hemangioendothelioma is important.