Microscopic features. A nested growth pattern of epithelioid tumor cells with clear to lightly eosinophilic cytoplasm, prominent cell membranes, and interstitial lymphocytic infiltrate was characteristic (A), and occasional thick collagenous septa were present (B). At high-power, slightly irregular nuclear contours, vesicular chromatin, and prominent nucleoli were apparent (A, inset). Patchy, fine to slightly coarse cytoplasmic melanin (C) was confirmed histochemically with a Fontana-Masson silver stain (C, inset). Unique to this case were intratumoral sarcoid-like and granulomatous inflammatory reactions, including tightly formed, noncaseating epithelioid granulomas with conspicuous multinucleated giant cells and a lymphocytic cuff (D, E, F). Calcifications were prominent within foci of granulomatous inflammation. Focally these calcifications had a shell-like appearance as seen in Schaumann (conchoidal) bodies (E, inset).
Ritterhouse et al. Diagnostic Pathology 2014 9:81 doi:10.1186/1746-1596-9-81