Histogenesis of true splenic cysts: a histological and immunohistochemical study.

Three true splenic cysts were studied histologically and immunohistochemically using antibodies against Ber-EP4, CEA, factor-VIII related antigen and several cytokeratins of varying molecular weights. Two cysts were lined by cuboidal and columnar cells with extensive squamous metaplasia. The columnar cells have the immunophenotype of mesothelial cells being positive for keratin but negative for Ber-EP4 and CEA. The third cyst occurred in a wandering spleen and was lined by hobnail columnar cells with cilia resembling tubal epithelium of Fallopian tube. The immunophenotype was that of epithelial cells being positive for both keratin and Ber-EP4. It is likely that true splenic cysts originate from invagination of the capsular mesothelial lining. The frequent occurrence of stratified squamous epithelium is attributed to squamous metaplasia secondary to haemorrhage and irritation. On the other hand, the presence of tubal epithelium in true splenic cysts is more likely to be due to the innate potentiality of mesothelial cells to differentiate along Mullerian line and may be a manifestation of the secondary Mullerian system. The cyst lining cells were negative for factor-VIII related antigen and thus offered no support for an origin from endothelium.