Ciliated hepatic foregut cyst. A mucus histochemical, immunohistochemical, and ultrastructural study in three cases in comparison with normal bronchi and intrahepatic bile ducts.

We describe herein the morphologies of three cases of ciliated hepatic cysts and compare them with those of normal bronchi and intrahepatic bile ducts. Grossly, the hepatic cysts were located in the subcapsular region. They were solitary, unilocular, and rather small (less than 4 cm in diameter). Histologically, the cyst wall consisted of four layers: pseudostratified ciliated columnar epithelia with mucous cells, subepithelial connective tissue, smooth-muscle bundles, and an outermost fibrous capsule. The epithelial cytoplasm contained neutral, carboxylated, and sulfated mucus. We noted moderate immunoreactivity to keratin, epithelial membrane antigen, carcinoembryonic antigen, DU-PAN-2 and secretory component; weak immunoreactivity to cytokeratin CAM 5.2, cytokeratin AE1 + 3, and carbohydrate antigen 19-9; and faint or negative immunoreactivity to IgA and IgM. Cilia were immunoreactive to actin and tubulin; smooth muscles were immunoreactive to actin and desmin. Ultrastructural observations revealed definite cilia arranged in a 9 + 2 pattern as well as mucous cells. These morphologic features of the hepatic cysts were similar to those of normal bronchi but different from those of normal bile ducts. Our findings suggest that ciliated hepatic cysts arise from the embryonic foregut and differentiated toward bronchial structures in the liver.