This video details the pathological examination of Case 3, a slow-growing, 4 cm soft tissue mass from the trunk of a 45-year-old male. Microscopically, the tumor is well-circumscribed and composed of bland spindle cells exhibiting a characteristic "whirling" or storiform growth pattern. Based on this morphology and the anticipated immunohistochemical profile (EMA+, Claudin-1+, Glut-1+, S100-), the diagnosis is confirmed as Perineurioma. The discussion highlights the diagnostic challenge of recognizing the whirling pattern and explores key entities in the differential diagnosis, including Dermatofibrosarcoma Protuberans (DFSP) and Low-Grade Fibromyxoid Sarcoma (LGFMS), emphasizing the use of MUC4 and CD34 to distinguish these tumors from the benign perineurioma.
Pathology Case Study: Perineurioma of the Trunk
0:00 Case Presentation: The case involves a 45-year-old man with a slow-growing, 4 cm soft tissue mass located on the trunk.
0:23 Gross Appearance: At low power, the mass is observed to be well-circumscribed and encapsulated.
0:40 Microscopic Pattern: The tumor is characterized by a "storiform" (pinwheel-like) and "whirling/swirling" pattern of cellular growth.
1:42 Proposed Workup: The trainee suggested an immunohistochemistry (IHC) panel including EMA, S100, Claudin-1, and Glut-1, which immediately narrows the focus.
2:11 Diagnosis: The final diagnosis is Perineurioma, a benign nerve sheath tumor.
2:02 Expected Immunophenotype: Perineuriomas typically stain positive for EMA, Claudin-1, and Glut-1, and negative for S100.
2:21 Pattern Recognition Difficulty: The presenter notes that the distinction between "whirling" (more circular) and "storiform" (spindled edges) can be highly subjective and difficult to reliably identify, even for experienced pathologists.
3:39 Differential Diagnosis (DFSP): The whirling/storiform pattern requires considering Dermatofibrosarcoma Protuberans (DFSP). Key distinguishing feature: Perineuriomas are usually circumscribed, while DFSP is typically infiltrated and traps adipocytes.
4:06 Differential Diagnosis (LGFMS): Low-Grade Fibromyxoid Sarcoma (LGFMS) must also be considered, as some variants can mimic the perineurioma's whirling pattern. LGFMS can be identified using MUC4 stain (positive).
4:27 Cell Morphology: Perineurial cells are bland, elongated spindle cells. Their appearance (thin vs. oval) is highly dependent on the plane of section, reflecting their structure as cells designed to wrap peripheral nerves.
5:17 Other Differentials: Rare soft tissue meningiomas (due to their similarity to meningothelial cells), Myofibromas (which whirl around vessels and are Actin+), and occasionally Solitary Fibrous Tumors (SFT) can also be in the differential diagnosis.
7:00 Key Takeaway: Perineuriomas are benign tumors.