Adrenal cyst with both Müllerian and mesothelial differentiation- a clinicopathological and immunohistochemical study with implications for histogenesis.

True epithelial-lined cysts are rare forms of adrenal cystic lesions, the pathogenesis of which is still not fully understood. In this report we present a case of an adrenal cyst diagnosed incidentally on imaging in a 31-year-old, previously healthy, obese woman. Due to non-specific hormonal disorders and enlargement of the lesion, a right-sided laparoscopic adrenalectomy was performed. The cyst was lined predominantly by ciliated cuboidal-to-columnar, Müllerian-type epithelium, and focally by flat-to-cuboidal, mesothelium-like lining. Immunohistochemistry demonstrated a strong positive reaction in the cells of both types of lining for CKAE1+E3, CK19, CK7 and WT1, and both had a negative reaction for CK20, CD34, Melan-A, SF1, TTF1, SMA and CDX2. The cells of the ciliated cuboidal-to-columnar epithelium were strongly positive for PAX8, ER, Ep-CAM and EMA, focally positive for PR, and were negative for calretinin, whereas the cells of the flat-to-cuboidal lining were positive for calretinin and podoplanin and showed only a weak positive response in individual cells for PAX8, EMA and Ep-CAM, but were negative for ER and PR. This is the first reported case of an adrenal ciliated epithelial cyst with Müllerian differentiation (confirmed immunohistochemically) in the English literature. The differences in morphology and immunophenotype of the two types of lining (epithelial Müllerian phenotype versus mesothelial phenotype), suggest that some adrenal epithelial cysts probably form due to metaplasia of mesothelium-derived lining. A similar mechanism may also be involved in the pathogenesis of at least some of the so-called Müllerian cysts (or inclusions) in other locations.