Ciliated hepatic cyst without smooth muscle layer: a variant of ciliated hepatic foregut cyst?

The ciliated hepatic foregut cyst (CHFC) is a rare lesion that may arise from remnants of the embryonic foregut. Its wall is lined by pseudostratified ciliated columnar epithelium, and is characterized by the presence of bundles of smooth muscle. Herein is presented two cases of ciliated hepatic cyst without smooth muscle layer. One case was an incidental autopsy finding, and the other was a surgically resected cystic lesion of the liver. Both cysts were <2.0 cm in diameter, and were located subcapusularly in the medial segment (S4) of the liver. The histological appearance of the two cases was identical. They had an epithelial lining of ciliated pseudostratified cells with occasional goblet cells, and lacked a smooth muscle layer, as shown by the actin immunostaining. The lining epithelium contained cells positive for immunohistochemical staining of surfactant apoprotein A, suggesting the embryonic foregut origin of the cysts and differentiation toward bronchiolar structures, rather than ciliated metaplasia of the epithelium of the simple (cholangiogenic) cyst. It is considered that ciliated hepatic cysts of the present case are a rare histological variant of CHFC where the smooth muscle layer is inconspicuous or absent.