Inflammatory pseudotumor of the spleen. Report of a case with an immunohistochemical study.

A 81-year-old Japanese man with a splenic inflammatory pseudotumor is described. The pseudotumor was unchanged in size after one year of observation. Macroscopically, the lesion was a firm well-circumscribed 5.5 x 5 x 5 cm mass showing a yellowish-white cut surface. Histologically, it was composed of abundant mixed inflammatory infiltrates, predominantly UCHL-1(+) T and L26(+) B lymphocytes, plasma cells containing various immunoglobulin subtypes, and S-100 protein(+), and lysozyme and NCA(+) histiocytes, with a sclerotic stroma. Small numbers of eosinophils, neutrophils and foamy macrophages were admixed. The patient has remained disease-free for 14 months after splenectomy. Only ten splenic inflammatory pseudotumors have been reported in the literature. This paper adds an additional case, together with details of immunohistochemical polyclonality of each inflammatory cell population, confirming that this disease is a nonspecific inflammatory change.