Large aneurysmal dermatofibroma mimicking melanoma in an adolescent: A case report

Hemosiderotic dermatofibroma (HDF) is an infrequent variant of dermatofibroma, made up of small blood vessels, hemosiderin deposits, and extravasated erythrocytes. HDF closely resembles melanoma, with irregular borders and colour changes on clinical examination and atypical cell organization on dermoscopy and can pose a diagnostic dilemma. We report the case of a large (5cm) subcutaneous hemosiderotic/aneurysmal DF (H/ADF) that appeared on the flank of 17-year-old, otherwise healthy, male patient. The mass evolved over two years, with purple discoloration noticed three months prior. Clinical examination revealed a palpable moveable mass overlying the left hip in the subcutaneous tissues measuring approximately 4 x 4 cm. Because of both the substantial size of the mass and diagnostic uncertainty, the decision was made to proceed with surgical resection. The lesion was resected without complication, although there was copious bleeding initially. Pathological findings showed a dermatofibroma, cellular subtype, with aneurysmal change. Sections showed a solid, cellular proliferation composed of plump ovoid to spindle cells arranged in a storiform pattern and short fascicles punctuated by areas of hemorrhage and associated hemosiderin pigment deposition. Occasional multinucleated giant cells were seen. At 1 month follow-up, the patient was in good condition, and completely asymptomatic. There was no recurrence. Pediatric surgeons should be aware that rare dermatofibroma variants, such as aneurysmal dermatofibroma, can clinically resemble melanoma and should be treated with excisional biopsy. Diagnosis should always be confirmed with histopathology and immunohistochemistry.