Follicular Variant of Hyaline-vascular Type of Castleman's Disease : Histopathological and Immunohistochemical Study of 11 Cases

Occasionally, the hyaline-vascular type of Castleman's disease (HVCD) contains numerous lymphoid follicles which usually occupy more than 50% of the lesion. Such lesions are called the follicular variant (FV) of HVCD. To clarify the histological and immunohistochemical findings of lymphoid follicles in the FV of HVCD, we examined 11 such cases. Histologically, five types of lymphoid follicles were delineated. Lymphoid follicles; (i) with normal germinal centers (GCs); (ii) showing follicular lysis; (iii) with progressive transformation of GC (PTGC); (iv) where the large nodule of mantle zone lymphocytes contained multiple small atrophic GCs (multiple GC pattern); and (v) where the large, often irregularly shaped nodules of mantle cells radically penetrated small vessels with inconspicuous GCs. These nodules somewhat resembled primary lymphoid follicles (primary follicular pattern). The majority of lymphoid follicles in all 11 cases were of the primary follicular pattern and/or multiple GC pattern. However, three lesions also contained normal germinal GC, while two contained normal GC, follicular lysis and PTGC and one other contained normal GC and PTGC. Moreover, in 3 cases of primary follicular pattern, the majority of the lymphoid follicles were surrounded by a pale cuff of mantle cells. Because of the presence of numerous lymphoid follicles, the FV of HVCD should be sometimes differentiated from Hodgkin lymphoma and low-grade B-cell lymphomas showing follicular growth pattern. Recognition of the histological and immunohistochemical findings of the FV of HVCD is needed to avoid overdiagnosis.