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| Fig. 43.6 Hemosiderotic dermatofibroma. A clinical and histologic variant of dermatofibroma with fibrohistiocytic cells demonstrating phagocytosis of hemosiderin. Because of the color, they are clinically often confused with vascular tumors, but on palpation they are typically firm. (Courtesy of the Fitzsimons Army Medical Center teaching files.) |
What is a dermatofibroma? A dermatofibroma, or fibrous histiocytoma, is the most common fibrohistiocytic tumor of the skin. Usually, these are small, firm, flat, or exophytic papules on the lower extremities of adults. Alhough most commonly 2 to 4 mm in diameter, they can occasionally grow to 2 to 3 cm. They may be skin-colored but more commonly demonstrate tan or brown hyperpigmentation and hypertrophy of overlying epidermis. Nondermatologists frequently mistake them for nevi. Other common locations include the sides of the trunk and upper arms.
Microscopically, most dermatofibromas are composed primarily of fibroblasts that produce abundant collagen. Within some, but not all, dermatofibromas, there are often cellular areas composed of cells with round nuclei that phagocytize lipid or hemosiderin. Multinucleated giant cells may also be present. Dermatofibromas that phagocytize abundant hemosiderin molecules are sometimes referred to as hemosiderotic dermatofibromas or sclerosing hemangiomas (Fig. 43-6).
