Collapsing angiokeloidal dermatofibroma.

A heterogeneous group of benign fibrohistiocytic lesions has been assembled under the umbrella term, dermatofibroma. These lesions share a morphology of bland spindled cells encompassed by and intercalating through thick dermal collagen; unique variants have been described based on secondary histologic features, some of which include aneurysmal, myxoid, lipidized, signet ring, angiomatous, and keloidal. Here, we present a distinct dermatofibroma variant henceforth known as collapsing angiokeloidal dermatofibroma identified in 2 patients with slowly growing nodules of the buttock and the arm. Microscopically, the lesions have a characteristic dermatofibroma appearance but are accompanied by unusual diffuse small caliber vessels whose walls are collapsed by a thick, eosinophilic, keloid-like substance. The eosinophilic material resembles the adjacent dermal collagen; however, it does not stain for type-4 collagen or type-1 procollagen, amyloid, or glycogen. Although the exact composition of the keloidal material remains ambiguous, the architectural novelty of collapsing angiokeloidal dermatofibroma serves to further expand the morphologic spectrum of benign fibrous histiocytomas, although highlighting the difficulty in distinguishing between it and similar lesions.