Abstract

Cutaneous silica granulomas are an uncommon subset of foreign body granulomatous reactions. Histopathologically, they are characterized by sarcoid-like epithelioid histiocyte aggregates and multinucleated giant cells with the presence of crystals. Asteroid bodies, a typical histopathological feature of sarcoidosis and certain infections, have not previously been reported in association with silica granulomas. Herein, we present a case of an 83-year-old man with a history of cutaneous squamous cell carcinoma, prostate cancer, and hypothyroidism who presented with a 3 cm depressed, pinkish plaque on the vertex scalp. Given clinical concern for malignancy, a shave biopsy was obtained. Histologic examination revealed a dermal granulomatous reaction to birefringent, crystalline foreign bodies consistent with silica crystals. Multiple asteroid bodies were observed in the cytoplasm of multinucleated giant cells in close proximity to the crystals. In the absence of systemic symptoms or findings suggestive of sarcoidosis and given the clinical presentation, a final diagnosis of silica granuloma with asteroid bodies was made. While asteroid bodies have been observed in several granulomatous reactions, such as sarcoidosis, tuberculosis, sporotrichosis, and silicone granulomas, the present case represents a novel association of asteroid bodies with silica granulomas. The composition of asteroid bodies and the mechanisms of their formation remains a matter of ongoing investigation, though existing evidence suggests they are products of microtubular disarray or collagen trapping. While rare, the case suggests that asteroid bodies can occur in foreign body reactions in the absence of sarcoidosis.

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