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Stroma-Rich Castleman's Disease with Superimposed Kikuchi's Lymphadenitis-Like Changes

The authors report a retroperitoneal lesion showing the hitherto undescribed coexistence of hyaline-vascular Castleman's disease and Kikuchi's lymphadenitis-like changes, the only feature in common for these two disease processes being the consistent presence of plasmacytoid monocytes (plasmacytoid T-cells). The Castleman's disease was classifiable as the stroma-rich variant, with broad interfollicular zones occupying 90% of the cross-sectional areas. The interfollicular regions were rich in atypical plump spindly cells with indistinct cell borders, oval nuclei, vesicular chromatin, and distinct nucleoli; they were disposed in fascicles and whorls around and between the hyaline-vascular follicles. The exact nature of these atypical stromal cells could not be ascertained because they were immunohistochemically inert except for vimentin expression. Scattered throughout the interfollicular areas were multiple discrete foci comprising plasmacytoid monocytes, karyorrhectic debris, activated lymphoid cells, histiocytes with twisted nuclei and crescentic histiocytes, as characteristic of Kikuchi's lymphadenitis. Although the coexistence of Castleman's disease and Kikuchi's lymphadenitis-like changes can be coincidental, it is also possible that the latter might represent an unusual aberrant local immune reaction to the stromal overgrowth in the Castleman's lesion.