All the histological types may occur in the skin. There is a nodular, well-circumscribed infiltrate involving the dermis and subcutaneous tissue with a prominent follicular
Figure 1 Castleman disease: onion skin-like arrangement of lymphocytes around a central vessel.
growth pattern. Most of the follicles demonstrate atrophic germinal centers and concentric rings of small lymphocytes penetrated by interfollicular capillaries. Multinucleated giant cells resembling the Warthin-Finkeldey cells seen in measles can be observed in some germinal centers. There is also a mixed infiltrate of epithelioid histiocytes and lymphoplasmacytoid cells and large numbers of small vessels with thickened hyalinized walls. The PC type is distinguished by abundant sheets of mature plasma cells in the interfollicular areas and displays little hyalinization of vessels. The HV variant is typified by marked perivascular hyalinization of collagen which can be radially arranged around vessels with thick hyalinized walls (Fig. 1). The HV type seems to predominate in cases with subcutaneous involvement (9).
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