This video, presented by Jarrett Gardner and Dr. Edie Fulton, offers a comprehensive pathological review of perineuroma, a benign soft tissue tumor. It meticulously describes the tumor's characteristic microscopic features, including bland spindled cells forming distinctive swirling and whirling patterns, often concentrically arranged around vessels, with oval-to-spindled nuclei and thin, bipolar cytoplasmic processes. The discussion highlights soft tissue and sclerosing variants, with the latter typically presenting on acral skin with dense collagen and cells arranged in cords or chains. A significant portion of the video addresses the crucial differential diagnosis, distinguishing perineuroma from entities such as neurofibroma, dermatofibrosarcoma protuberans (DFSP), low-grade fibromyxoid sarcoma (LGFMS), myoepithelioma, and soft tissue meningioma. It details the immunohistochemical profile for perineuroma (EMA, Claudin-1, GLUT1 positive; S100 negative) and provides strategies for utilizing a panel of stains and molecular testing (for DFSP and LGFMS translocations) to achieve an accurate diagnosis, underscoring the vital prognostic implications for patient management.
Details: These tumors typically form nodules measuring 1-10 cm (most commonly around 3 cm).
Key Takeaway: They usually arise in the subcutis, though they can also be found in the dermis or deep soft tissue.
0:09 Microscopic Hallmarks - "Whirling and Swirling":
Details: The most crucial microscopic feature is spindled to ovoid cells arranged in swirling, whirling, or concentric lamellar patterns, often centered on small blood vessels. The cells are flat, disc-shaped, causing their nuclei to appear oval or spindled depending on the plane of section, and possess long, thin, bipolar cytoplasmic processes. Nuclear atypia and mitotic activity are typically absent or very rare.
Key Takeaway: This characteristic growth pattern, combined with bland cytology, is key for diagnosis. Significant atypia or numerous mitoses should raise suspicion for other entities.
Details: Normal perineural cells, similar to meningeal cells, wrap and swirl around nerve bundles, providing protection. This inherent tendency is recapitulated in perineuroma's growth pattern.
Key Takeaway: The unique morphology and function of perineural cells explain the tumor's characteristic appearance.
Details: The video focuses on soft tissue perineuroma (classic whirling patterns, sometimes with myxoid change) and sclerosing perineuroma. Other rare forms like intra-neural and reticular perineuroma exist but are not covered in depth.
Key Takeaway: Sclerosing perineuroma typically occurs on acral skin (e.g., hands/fingers), features dense collagen, and cells often align in cords or chains, although whirling patterns can still be seen focally.
Details: Many perineuromas can exhibit bluish mucin or myxoid (hyaluronic acid) change, and/or a prominent collagenous background, sometimes with delicate, stacked lamellar layering.
Key Takeaway: These features are important for differential diagnosis, particularly with low-grade fibromyxoid sarcoma.
Details: While perineuromas are usually circumscribed, rare infiltrative cases may show extensive entrapment of adipose tissue in a "honeycomb" pattern.
Key Takeaway: This growth pattern is highly suspicious for Dermatofibrosarcoma Protuberans (DFSP) and warrants immediate molecular workup to distinguish from perineuroma due to significant prognostic differences.
Positive in Perineuroma: EMA (often weak/patchy, highlights processes), Claudin-1 (stains most perineuromas, highlights streaming processes), GLUT1 (strong, highlights streaming processes). CD34 is positive in ~60% of cases, often patchily.
Negative in Perineuroma: S100.
Key Takeaway: A panel including EMA, Claudin-1, and GLUT1 is highly suggestive of perineuroma. S100 negativity helps rule out neurofibroma and most myoepitheliomas.
DFSP: Strong diffuse CD34 positivity and COL1A1-PDGFB translocation (17;22) are characteristic. Perineuroma's patchy/negative CD34 is helpful.
LGFMS: MUC4 positivity and FUS-CREB3L1/2 translocations are diagnostic. Claudin-1 can be positive in LGFMS, but GLUT1 is typically negative.
Meningioma (Soft Tissue): Shares EMA positivity and swirling patterns. PR and SSTR2 are positive in meningioma but rarely in perineuroma. A panel of EMA, Claudin-1, GLUT1, PR, and SSTR2 helps.
Key Takeaway: Accurate diagnosis is critical for patient care; perineuromas are benign, while DFSP and LGFMS are malignant or locally aggressive and require different management. Molecular testing is crucial in equivocal cases.