This is an unusual variant of dermatofibroma, a benign fibrohistiocytic tumor. One can call it a hemosiderotic dermatofibroma or an aneurysmal dermatofibroma, depending on the relative contribution of the vascular component. The presence of pigment may scare the untrained eye, but this pigment is hemosiderin. The differential diagnosis would include a melanocytic or vascular lesion. One must look to the periphery of the lesion to find the more traditional patten of a dermatofibroma.
Description
There is a fibrohistiocytic proliferation within the dermis. The overlying epidermis is mildly thinned with overlying scale. Within the proliferation, there are large cavernous blood-filled spaces. At the periphery of the lesion, the spindle cells trap collagen bundles.
