This video clip focuses on the pathological characteristics of a specific variant of dermatofibrosarcoma protuberans (DFSP). The case exhibits the classic DFSP feature of fat entrapment with a honeycomb pattern but is noteworthy for the presence of numerous pigmented spindle cells containing melanin. This specific microscopic finding earns the tumor the eponym of a Bednar tumor (pigmented DFSP). The speaker emphasizes that this pigmentation is a "microscopic curiosity" and does not alter the clinical behavior or necessary treatment compared to conventional DFSP. A crucial differential diagnosis—pigmented diffuse neurofibroma—is discussed, and immunohistochemical markers (S100/SOX10) are recommended to distinguish it from DFSP, as both entities typically express CD34.
Summarizing the Pathological Findings of a Bednar Tumor
0:00:11 Fat Entrapment: The specimen displays classic DFSP features, including prominent fat entrapment in a honeycomb pattern, though this particular case lacks epidermal hyperplasia.
0:00:26 Pigmented Spindle Cells: A special finding is the presence of pigmented spindle cells, identified as melanin-producing melanocytes, scattered throughout the tumor. Staining confirms the pigment as melanin (positive for Fontana Masson, negative for iron stain).
0:01:06 Eponym (Bednar Tumor): The presence of these pigmented cells dictates the formal designation of the tumor as a Bednar tumor (or DFSP with focal melanin pigment).
0:01:25 Clinical Takeaway: The speaker emphasizes that Bednar tumor is functionally the same as regular DFSP; the pigmentation is a microscopic finding that does not change the behavior or treatment protocol.
0:01:34 Differential Diagnosis: An important distinction must be made against pigmented diffuse neurofibroma, as both tumors can look similar microscopically and both typically express CD34.
0:01:54 Diagnostic Confirmation: To resolve the differential, use immunohistochemical stains like S100 or SOX10. These neural markers are positive in neurofibroma but are almost always negative in DFSP.