This video provides a detailed pathological review of perineuroma, a benign soft tissue tumor originating from perineural cells. Microscopically, the tumor is characterized by bland, spindle-to-oval cells exhibiting a distinct "whirling and swirling" (storiform-like) growth pattern, often forming concentric, lamellar layers around small blood vessels. The lecture highlights the cellular morphology, explaining how the flat, disc-shaped perineural cells appear oval or spindled depending on the plane of section. Key differential diagnoses include neurofibroma, dermatofibrosarcoma protuberans (DFSP), and low-grade fibromyxoid sarcoma (LGFMS). Differentiation relies heavily on immunohistochemistry (IHC): Perineuromas are S100-negative and ideally express EMA, Claudin-1, and GLUT-1. The video stresses the clinical importance of ruling out DFSP (particularly when fat entrapment is present) and LGFMS, often necessitating the use of extended IHC panels (CD34, MUC4) or molecular testing (FISH/RT-PCR) due to overlapping marker expression.
Perineuroma: A Pathological Review of a Benign Spindled Tumor
0:03 Benign and Uncommon Tumor: Perineuroma is a benign, relatively uncommon soft tissue tumor composed of perineural cells, offering an excellent prognosis for patients.
0:42 Clinical Presentation: These tumors typically present as nodules a few centimeters in size (most around 3 cm) and usually arise in the subcutis, though they can occur in the dermis or deep soft tissue.
1:09 Classic Morphology (Swirling): The hallmark microscopic feature is bland, spindled cells exhibiting a prominent "whirling and swirling" growth pattern, often forming concentric, lamellar circles centered on small blood vessels.
2:45 Cytological Atypia/Mitoses: Perineuromas are typically very bland with little nuclear atypia and absent or very rare mitotic activity. High-grade features should prompt consideration of malignant peripheral nerve sheath tumor (MPNST).
4:31 Nuclear Appearance: The cells are essentially flat, oval discs. Nuclei appear oval when sectioned face-on and spindled when sectioned on edge, explaining the variability in nuclear shape. The cells also feature thin, tapered, bipolar cytoplasmic processes.
6:56 Circumscription and Mixoid Change: Perineuromas are usually well-circumscribed but can occasionally be infiltrative. They frequently contain variable amounts of blueish mucin or myxoid (hyaluronic acid) change in the background (11:48).
10:17 Variants: The video focuses on Soft Tissue Perineuroma and Sclerosing Perineuroma. Sclerosing perineuroma typically occurs on acral skin (hands/fingers) and is characterized by dense collagen and cells organized into chords or chains (22:46).
28:09 Perineural Immunohistochemistry (IHC): Perineuromas are typically S100 negative (ruling out neurofibroma) and stain for perineural markers: EMA (often focal/weak), Claudin-1 (30:06), and GLUT-1 (32:57).
32:38 IHC Overlap & Specificity: EMA and Claudin-1 positivity is not specific; they can occasionally stain DFSP and LGFMS, making GLUT-1 useful as it is usually negative in these differential diagnoses.
34:03 Panel and Molecular Testing: Distinguishing between perineuroma (benign) and DFSP/LGFMS (malignant) is crucial.
DFSP: Typically diffuse, strong CD34 positive (Perineuroma is often negative/patchy) and confirmed by the COL1A1-PDGFB translocation.
LGFMS: Confirmed by MUC4 positivity and FUS-CREB3L1/2 translocations.
36:25 Meningioma Differential: Extraspinal meningiomas (which swirl and are EMA positive) are differentiated by their positivity for SSTR2 and Progesterone Receptor (PR), markers typically negative in perineuroma.