Pediatric pigmented dermatofibrosarcoma protuberans (Bednár tumor): case report and review of the literature with emphasis on the differential diagnosis.

Dermatofibrosarcoma protuberans (DFSP) is a fibrous tumor of intermediate malignant potential that usually affects the trunk of young to middle-aged adults. On histological examination, it is characterized by a monomorphous population of spindle cells arranged in a storiform or cartwheel pattern. Bednár tumor (BT), formerly known as storiform pigmented neurofibroma, is currently considered the pigmented variant of DFSP due to the histological and cytogenetic similarities between these two lesions. There are very few reports on BT affecting pediatric patients. We describe a case of BT affecting the dorsal aspect of the left forearm of a 6-year-old-male patient and emphasize the diagnostic clues to distinguish this unusual cutaneous neoplasm from other pigmented lesions, including pigmented (melanotic) neurofibroma (PMN), psammomatous melanotic schwannoma (PMS), neurocristic cutaneous hamartoma (NCH), and desmoplastic malignant melanoma (DMM). We would like to stress that surgical pathologists and dermatopathologists need to be aware of the prototypical histological appearance of BT as there is the risk of misdiagnosing it either as pigmented tumors associated with neurocutaneous syndromes, such as PMN and PMS, or as a highly malignant melanocytic neoplasm (DMM).