Giant aneurysmal benign fibrous histiocytoma (dermatofibroma).

Aneurysmal benign fibrous histiocytomas are variants of dermatofibromas. These benign blood-filled lesions can mimic malignancies due to their rapid and recurrent growth. Our patient is a 42-year-old Caucasian female with a past medical history of morbid obesity, diabetes, and hypertension, who presented with a mass on her left shoulder for 5 years' duration. The mass oozed occasionally and would appear to regress but then recur replaced with progressively larger masses. Upon inspection, the patient had a large pedunculated exophytic mass with vascularity. The mass was surgically removed under general anesthesia via wide local excision. Grossly, the excised skin was purple-tinged with an underlying fungating solid mass measuring 8.5 cm. Serial sections revealed a hemorrhagic, spongy, and granular cut surface. Histologically, the epidermis was hyperplastic, with underlying hyaline collagen bundles. The remainder of the mass was chronically inflamed and composed of spindled histiocytes, hemosiderin-laden macrophages, and blood-filled spaces lacking an endothelial lining. There was focal pleomorphism but no significant atypia. Immunohistochemical stains were strongly positive for vimentin and negative for CD31, CD34, and desmin. The overall architecture and immunophenotype are consistent with the diagnosis of aneurysmal benign fibrous histiocytoma.