The distinction of bronchogenic cyst from metastatic testicular teratoma: a light microscopic and immunohistochemical study.

Bronchogenic cyst (BC), a rare developmental abnormality of the primitive foregut and usually found above the diaphragm, can occur in the retroperitoneum and other unusual locations where distinction from metastatic teratoma is essential. We studied 22 BCs and 34 teratomas metastatic to the retroperitoneum in men. Of 22 BCs, 17 (77%) showed well or moderate architectural differentiation toward normal tracheobronchial structures, whereas none of the teratomas did. In addition, 20 (91%) of the BCs had respiratory-type epithelium and none had enteric-type epithelium. Immature elements, atypia, and tumor necrosis were absent in BCs. All BCs expressed cytokeratin (CK) 7, and none expressed CDX-2 in immunohistochemical analysis. Teratomas had mixed enteric and respiratory-type epithelium. The majority of the glands were positive for CK7 (33 [97%]), CK20 (34 [100%]), CDX-2 (34 [100%]), and thyroid transcription factor (TTF)-1 (17 [50%]). Coexpression of CDX-2 and TTF-1 was found in 11 teratomas (32%) but none of the BCs. BCs can be reliably distinguished from teratomas based on the gross, histologic, and immunohistochemical features.