Abstract

A 23-year-old Fitz II female with no significant past medical history presented for evaluation of a lesion on left anterior shin. Patient reported that the lesion had been present for several years but began to expand and bleed about 1.5 years ago. The lesion plateaued in size over the past year and had not caused further issues. On physical exam at the time of dermatology visit, the patient had a 2cm firm, well circumscribed, violaceous plaque on the left anterior shin. A 4mm punch biopsy was performed. H&E revealed spindled cells throughout the dermis, epidermal acanthosis, and entrapment of collagen bundles at the periphery with abundant hemosiderin. Immunostains were performed to rule out dermatofibrosarcoma protuberans or other malignancies. The spindle cells were positive for Factor XIIIa and negative for CD34. ERG was also expressed, which highlighted blood vessels within the lesion. Based on clinical, histopathologic, and immunochemistry findings, the lesion was diagnosed as hemosiderotic dermatofibroma. Dermatofibromas are most commonly found on the extremities in young to middle aged adults with a female predominance. Hemosiderotic dermatofibromas are a rare variant, comprising only about 2% of all dermatofibromas. Another significance of these lesions is that they can mimic melanoma or vascular tumors on dermoscopy. It is believed that erythrocytes extravasate from small vessels leading to cavitary dilations lacking an endothelial lining. For this reason, they are thought to be an early stage of aneurysmal dermatofibroma. Complete excision is the recommended treatment as these lesions often recur.

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