Dermatofibroma of the Auricle

CASE PRESENTATIONA 14-year-old male presents to the office with a 3-month history of a small mass behind the left ear associated with discomfort only when applying pressure. The patient also has a history of chronic rhinitis, which has been controlled with saline rinses and bactroban ointment. He has no past medical history or surgical history. He takes no medications, and has no allergies. His family history is only remarkable for hypertension on his father’s side. Physical exam reveals a left sided one cm fixed bluish lesion on the superior sulcus of the posterior ear. The external auditory canal and tympanic membrane are within normal limits bilaterally. The remainder of the examination is unremarkable.The patient was taken to the operating room to remove the mass, which was found to be a 10 mm x 8 mm well-encapsulated bluish mass (Figure 1). The patient treated surgery well. The mass was sectioned and the cut-surface revealed a gritty texture with a variegated appearance. Histopathologic analysis of the specimen revealed the presence of histiocytes and fibroblastic spindle cells with rare mitotic figures and no evidence of atypia or pleomorphism (Figure 2). The specimen was stained for vimentin, factor XIIIa (Figure 3), CD68 (Figure 4), smooth muscle actin, and CD34.A diagnosis of dermatofibroma, cellular type, was made and the patient required no additional treatment. The patient did well after surgery, without any complications. He returned for follow up 3 months after the surgery and was found to have complete resolution of the mass without any evidence for recurrence.

Dermatofibroma, also known as benign fibrous histiocytoma, is a benign tumor of mesenchymal origin predominantly composed of a biphasic population of fibroblastic and histiocytic cells. While this commonly found tumor can arise on any body surface, it is most commonly found on the extremities, with a predilection for the lower legs. Although rare in the head and neck, it has been reported in the tongue, gingiva, mandible, maxilla, and both the upper and lower lip. Chronic irritation and trauma have been cited as possible risk factors, but causality has not been established.¹Dermatofibroma typically presents as a non-aggressive, slow growing, firm, reddish-brown mass that is well circumscribed.² When examined histologically, epidermal hyperplasia can be seen along with hyperpigmentation of the basal layer and an elongation of the dermal papilla separated by a clear grenz zone.¹ The neoplasm is composed of fibroblasts and histiocytes. Mitotic figures and cellular atypia are rare findings. Sectioned specimen will often stain positive for vimentin, CD38, and factor VIIIa.³Early lesions have been found to be reactive for CD68 and other macrophage markers.⁴ Early lesions also demonstrate peripheral positivity to factor VIIIa, which diminishes with the age of the lesion and is often times absent in atrophic dermatofibroma.⁵ Dermatofibroma can be histologically similar to nodular fasciitis, low-grade myofibroblastic sarcoma, and neurofibroma; as such, it must be differentiated. Nodular fasciitis may also have spindle cells in a storiform pattern, but has fascicles separated by myxoid stroma and displays S-100 positivity which dermatofibroma does not.⁶ Low-grade myofibroblastic sarcoma has poorly defined fascicles with atypical myofibroblastic cells that show invasion into adjacent structures in a diffuse pattern. The tumor cells stain positive for desmin, a marker dermatofibroma is generally negative for.⁷ Neurofibroma is also characterized by S-100 positivity, but shares the presence of spindle shaped cells with dermatofibroma.⁸Of the three types of dermatofibroma, cellular, epithelioid, and aneurysmal, cellular is more commonly found on the