Mesothelial cysts of the spleen with squamous metaplasia.

Epidermoid cyst (metaplastic mesodermal cyst) is the most common true cyst of the spleen. The pathogenesis is unknown. The lesion is usually asymptomatic and has a characteristic gross morphology. Two splenic epidermoid cysts which were mesothelial-lined and showed focal squamous metaplasia were observed. Examination of one adult spleen and ten fetal spleens showed similar mesothelial linings of their capsules. It is believed that the epithelial-lined splenic cysts are the result of invagination of capsular surface mesothelium with subsequent cystic expansion and metaplastic changes. The use of the term "mesothelial cyst with squamous metaplasia" as a more accurate term than "epidermoid" or "metaplastic mesodermal cyst" is suggested.