Immunohistological findings of suppurative granulomas of Yersinia enterocolitica appendicitis: a report of two cases.

We report on the histopathologic and immunohistologic findings of two cases of suppurative granulomatous appendicitis of Yersinia enterocolitica (Y. ent.). Using formalin-fixed, paraffin-embedded materials, polymerase chain reaction revealed Y. ent. in both cases. Histologically, the epithelioid cell granulomas (EPGs) were transmural in both cases. The EPGs were predominantly nonsuppurative, and were surrounded by a lymphoid cuff composed of small lymphocytes. A portion of EPGs contained suppuration of the centers of the granulomas (central microabscesses). The EPGs were composed of numerous histiocytes with or without epithelioid cell features, along with scattered small T-lymphocytes and plasmacytoid monocytes. None of the EPGs contained monocytoid B-cells. Immunohistochemical study demonstrated that EPGs were usually surrounded by surface IgM/D+ small mantle zone lymphocytes. Moreover, CNA.42 immunostaining occasionally demonstrated residual follicular dendritic cells in the center of the EPGs. The overall histomorphologic and immunohistochemical findings demonstrated that the EPGs with Y. ent. are of the B-cell negative hypersensitivity type and occur in reactive germinal centers. In one case, regional lymph nodes contained EPGs showing the same histologic and immunohistologic findings as those of the appendix. The present study indicates that among abscesses forming epithelioid granulomatous lesions, EPGs with Y. ent. were B-cell negative granulomas, and it demonstrates histopathologic and immunohistochemical findings different from those of cat scratch disease and lymphogranuloma venerum, which contain numerous monocytoid B-cells.