This pathology case study examines a firm papule on the finger, initially sent for excision as a "rule out cyst." Microscopic analysis reveals a dermal nodule characterized by a dense proliferation of spindle and ovoid cells exhibiting prominent "whirling and swirling" growth patterns, leading to the diagnosis of Perineuroma. Immunohistochemical (IHC) testing confirms the diagnosis, showing positivity for CD34 and Epithelial Membrane Antigen (EMA). A key focus of the discussion is the necessary differential diagnosis against Dermatofibrosarcoma Protuberans (DFSP), which shares CD34 positivity and a similar pattern but lacks the perineurial characteristics. The video also reviews the use of alternative perineurial markers (GLUT1, Claudin) and concludes by illustrating the morphologically distinct variant, Sclerosing Perineuroma. Perineuroma is highlighted as a benign tumor requiring only simple excision.
Pathology Case Review: Perineuroma vs. DFSP and Other Spindle Cell Lesions
0:11 Case Introduction and Clinical Context: The case involves a firm papule on the finger, often clinically misclassified as a cyst.
0:59 Key Histological Features: The dermal nodule consists of spindle and oval cells suggesting a neural or perineurial origin. The dominant feature is the pronounced whirling and swirling growth pattern, which is characteristic of Perineuroma.
1:17 Differential Diagnosis (Ddx): Initial considerations included fibroma, giant cell tumor of the tendon sheath (GCTTS), and palisaded encapsulated neuroma (PEN). GCTTS and fibroma were largely excluded due to the tumor’s superficial location in the skin.
3:40 Perineurial Cell Morphology: The cells are described as having an oval-shaped plate structure; they appear either thin and spindled (when cut longitudinally) or oval/round (when cut tangentially).
4:15 IHC Staining (CD34): The tumor is strongly positive for CD34.
5:01 Critical Differential (Perineuroma vs. DFSP): Perineuroma must be differentiated from Dermatofibrosarcoma Protuberans (DFSP). Both tumors are CD34 positive and can exhibit whirling/storiform growth.
Takeaway: DFSP often shows fat trapping/honeycomb pattern, and definitive distinction relies on molecular testing for collagen 1A1 PDGFR-beta or PDGF-D rearrangements, which are negative in Perineuroma.
6:19 IHC Staining (EMA): The tumor is positive for Epithelial Membrane Antigen (EMA). EMA also stains the normal perineurium around nerves, serving as a useful internal control.
Note: EMA is mentioned as a technically challenging stain in practice.
8:12 Alternative Perineurial Markers: GLUT1 and Claudin are also reliable markers that highlight the long, thin cytoplasmic processes of the perineurial cells.
9:18 Ruling Out Hybrid Tumors: A pure Perineuroma is expected to be negative for neural markers like S100 and Sox10. Positivity for these markers suggests a hybrid nerve sheath tumor (e.g., neurofibroma with a perineurial component).
10:11 Key Takeaway (Prognosis): Perineuroma is a benign tumor that is typically cured by simple local excision.
11:04 Sclerosing Perineuroma Variant: This variant, also seen on acral skin, is introduced. It has a significantly different, more highly sclerotic (hyalinized) background and features rounded/oval cells often arranged in chains/cords, making it easily confused if one is only familiar with the conventional type.