Endobronchial plasma cell granuloma (xanthomatous pseudotumor); a light and electron microscopic study.

Plasma cell granuloma (xanthomatous pseudotumor) is polymorphic at light as well as electron microscopic examination. At light microscopy the endobronchial variant of this entity was rich in plasma cells and interwoven, whorl-like, or concentrically arranged spindle cells. Foamy histiocytes and macrophages usually abundant in the intrapulmonary variant were rare. At electron microscopy particles 20 to 50 nm. in size were found at the bronchial mucosal surface but not elsewhere in the lesion. Plasma cells near the bronchial surface contained cytoplasmic fibrils, mitochondria with concentric cristae, and inclusions that bore a close resemblance to adjacent extracellular crystallized hemoglobin. Those in the center of the lesion ordinary round inclusions and none of the other changes. Spindle cells in the interlaced areas were mostly fibroblasts or myofibroblasts, whereas those whorled around capillaries resembled pericytes with basement membranes and nuxes-like intercellular junctions. Year rings like multilayered basal laminae were frequently present between the pericyte-like cells and the endothelial cells of the capillaries. The ultrastructure of plasma cell granuloma, like the histologic and clinical aspects, differs from that of sclerosing hemangioma, pseudolymphoma, and malignant plasma cell tumor affecting the lung.