Bronchogenic cysts in rare sites (retroperitoneum, skin, spinal cord and pericardial cavity): A case series and characterization of epithelial phenotypes.

Bronchogenic cysts are congenital malformations of the bronchial tree, detected as a cystic and/or mass lesion in the thoracic cavity. Although it occurs in distant locations, such as skin and retroperitoneum, to the best of our knowledge, little is known about the components and phenotypes of the epithelium that line a bronchogenic cyst in rare sites. The present study reviewed 34 bronchogenic cysts that were surgically resected at Osaka Medical and Pharmaceutical University Hospital (Osaka, Japan) from January 1998 to December 2020. Bronchogenic cysts in rare sites were detected and diagnosis was confirmed based on the presence of pseudostratified, ciliated and/or columnar epithelium together with at least one of the following: Cartilage, smooth muscle or seromucous glands. The phenotypes of epithelium lining the cyst were characterized using immunohistochemical analysis. A total of six bronchogenic cysts in rare sites (two cases each in the retroperitoneum and skin and one case each in the cervical spinal cord and pericardial cavity) met the criteria for confirmation of the diagnoses. The epithelium lining the cyst stained positive for cytokeratin CK7 and thyroid transcription factor 1 (a marker expressed in thyroid follicles and bronchial epithelium) and negative for CK20, indicating that the phenotypes were similar to those of the respiratory epithelium. The present study demonstrated that a bronchogenic cyst can occur in rare sites, such as the retroperitoneum, skin, spinal cord and pericardial cavity, suggesting that it should be considered as a differential diagnosis before surgical approach to implement relevant management modalities such as follow-up, simple or radical resection.