Bronchogenic Cysts in Rare Sites (Retroperitoneum, Skin, Spinal Cord, or Pericardial Cavity): A Case Series and Characterization of Epithelial Phenotypes

Background: Bronchogenic cyst is a congenital malformation of the bronchial tree, detected as a cystic and/or mass lesion in the thoracic cavity. Although its occurrence in distant locations, such as the skin and retroperitoneum, has been reported, the components and phenotypes of the epithelium that line a bronchogenic cyst in rare sites have scarcely been evaluated. Case presentation: We reviewed 34 available bronchogenic cysts that were surgically resected at Osaka Medical and Pharmaceutical University Hospital from 1998 to 2020. We found several bronchogenic cysts in rare sites, and reconfirmed their diagnoses based on the following anatomopathological criteria: 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 the epithelium lining the cyst were characterized using immunohistochemical analysis. Six bronchogenic cysts in rare sites (two cases in the retroperitoneum, two cases in the skin, one case in the cervical spinal cord, and one case in the pericardial cavity) met the criteria for the reconfirmation of the diagnoses. The epithelium lining the cyst stained positive for cytokeratin CK7 and thyroid transcription factor 1 (a marker expressed in thyroid follicle, and bronchial epithelium), and negative for CK20, indicating that the phenotypes were similar to those of the respiratory epithelium. Conclusions: : This study shows that a bronchogenic cyst could occur in rare sites, such as the retroperitoneum, skin, spinal cord, and pericardial cavity, suggesting that it should be listed as a differential diagnosis before surgical resection in order to apply relevant management modalities.