This pathology case presentation examines a challenging tumor excised from the scalp of a 30-year-old woman. Morphologically, the large soft tissue mass of plump spindle cells, highly vascular areas, and distinctive staghorn/hemangiopericytoma-like vessels strongly suggested a Solitary Fibrous Tumor (SFT). The differential diagnosis also included Monophasic Synovial Sarcoma and Dermatofibrosarcoma Protuberans (DFSP). Despite the initial impression and the unusual absence of typical fat entrapment, the tumor was confirmed to be a rare and complex variant of DFSP. Key diagnostic features included the highly characteristic storiform (pinwheel) growth pattern and positive CD34 staining. The case was further complicated by focal areas of fibrosarcomatous transformation, an aggressive feature associated with a higher metastatic risk (15%). The discussion highlights that large DFSPs can obliterate subcutaneous fat, making the classic diagnostic feature of fat trapping extremely focal and thus increasing the potential for misdiagnosis.
Pathology Case Review: A Challenging Dermatofibrosarcoma Protuberans (DFSP) Mimicking SFT
0:12 Case Introduction: A 30-year-old woman presents with a large scalp mass.
0:23 Initial Morphology: The tumor is a soft tissue mass composed of spindle cells with variable cellularity and highly prominent, branching "staghorn" vessels (hemangiopericytoma-like pattern), often associated with Solitary Fibrous Tumor (SFT).
0:45 High-Power Features: Cells are bland, plump spindle cells with no obvious mitosis.
1:14 Differential Diagnosis: The pathologist proposes Solitary Fibrous Tumor (SFT) as the top diagnosis, considering also Dermatofibrosarcoma Protuberans (DFSP) and Monophasic Synovial Sarcoma. SFT was initially favored due to the lack of clear fat entrapment.
1:37 Proposed Workup: Stains suggested include CD34 (expected negative for Synovial Sarcoma) and STAT6 (to confirm SFT, if positive).
2:27 Final Diagnosis: The tumor is confirmed to be a tricky example of Dermatofibrosarcoma Protuberans (DFSP), despite its large size and minimal classic fat trapping. The tumor stained positive for CD34 (2:21).
2:30 Diagnostic Challenge (Fat Trapping): Large DFSPs, particularly those pushing against deep structures like the galea/skull (scalp), can overrun and destroy subcutaneous fat, leading to an artificially smooth border and obscuring the classic infiltrative fat-trapping feature.
4:18 Vascular Pattern: The staghorn vessel pattern is acknowledged as being present in many tumors, including SFT, Synovial Sarcoma, and large DFSPs, confirming it is not specific to SFT.
4:57 Key Diagnostic Clue (Storiform Pattern): A highly characteristic "whirling, swirling pinwheel" or storiform pattern of cell growth is identified, which is a key feature of DFSP.
6:17 Fibrosarcomatous Transformation (FST): Focal areas of FST are present, indicated by the loss of the storiform pattern and the presence of intersecting long fascicles forming a "herringbone" pattern.
7:05 Prognostic Takeaway: FST in DFSP increases the risk of metastasis to approximately 15% (compared to ~2% for typical DFSP). DFSP remains a locally aggressive disease prone to multiple recurrences, especially on the scalp.