Clinicopathological and immunohistochemical analysis of epithelial-lined (true) cysts of the adrenal gland with proposal of a new histogenetic categorization.

Epithelial- lined (true) cysts are rare lesions and until now the only information we had about their histogenesis was based on the analysis of a few cases. We retrospectively reviewed 8 cases of cysts with a true epithelial lining (confirmed immunohistochemically). The pathological findings and immunohistochemical analysis of the epithelial linings allowed for categorization of the cysts into 3 groups. Five cysts had pure mesothelial lining, which was flattened to cuboidal, and demonstrated a positive reaction for mesothelial markers (eg. calretinin, WT1), and a negative reaction for EpCAM, EMA, PAX8 and ER. Two cysts had cuboidal to flattened lining, the cells of which were diffusely or focally positive for mesothelial markers, for some epithelial markers (eg. EpCAM and EMA) and despite a lack of müllerian-type epithelium demonstrated a positive reaction for PAX8 and focally for ER. A cyst derived from adreno-hepatic fusion (AHF)-related intra-adrenal bile ductules was diagnosed in a right adrenal gland which was directly adherent to the liver, microscopically features of AHF were visible with intermingling of adrenal and liver parenchymal cells. The immunoreactivity pattern was similar among the preserved cells of the cyst-lining, the intra-adrenal bile ductules and the normal bile ductules in the adjoining liver parenchyma. On the basis of this case series from a single institution (8 presented now and 1 reported before) we propose a new histogenetic categorization of adrenal epithelial cysts into: 1. pure mesothelial cysts (the most common type), 2. mesothelial cysts with incomplete or complete müllerian metaplasia 3. AHF-related cysts.