January Case of the Month

Clinical History: A 1.8-cm solitary peripheral pulmonary nodule was resected in a 72-year-old woman with long-standing rheumatoid arthritis. The clinical suspicion was carcinoma or a rheumatoid nodule. Macroscopically, the nodule was tan-white and lobulated, with central necrosis and calcification as seen in Figure 1. Histologically, the nodule consisted predominantly of cytologically bland histiocytes and multinucleated giant cells with cytoplasmic inclusions and some background fibrosis (Figure 2). The histiocytes were positive for CD163 (Figure 3). The cytoplasmic inclusions were visible as unstained rhomboid/needle-shaped cytoplasmic inclusions in the CD163 stain (Figure 3) and accentuated in the Gram stain (Figure 4).

Small lymphoid nodules consisting predominantly of CD20-positive small B cells with moderately abundant clear cytoplasm were discernible at the border of the histiocytic lesion and the lung in association with abundant plasma cells showing kappa light-chain restriction using immunohistochemical staining, and intimate association with bronchial and alveolar epithelium (Figures 5 and 6; Figure 6 includes CD3, CD20, kappa and lambda light chains).

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