Intravascular Nodular Fasciitis Mimicking Thrombotic Complications in a 16-year-old male with May-Thurner Syndrome

Abstract Introduction/Objective Nodular fasciitis is a rare benign myofibroblastic proliferation commonly mistaken for malignant tumors due to its rapid growth and clinical presentation. May-Thurner Syndrome (MTS), characterized by compression of the left common iliac vein by the right common iliac artery, predisposes individuals to deep vein thrombosis (DVT). However, here we present a unique case of intravascular nodular fasciitis presenting as thrombotic complications in the context of MTS in a 16-year-old male. Methods/Case Report A 16-year-old male presented with progressive left hip and leg pain accompanied by recent swelling. Ultrasound revealed occlusive thrombi within the left side external iliac, common superficial femoral, and great saphenous veins, along with nonocclusive thrombi in left deep femoral vein. Magnetic resonance venography confirmed MTS and extensive thrombosis. Thrombectomy was done with fragments sent to pathology. Microscopic examination showed cellular areas with loose myxoid composition, proliferating spindle, myofibroblastic/fibroblastic, and stellate cells arranged in irregular bundles. Additional microscopic findings included mild cellular atypia, mitoses, focal macrophage aggregates, occasional multinucleate forms, foci of hemorrhage, fibrin exudate, ingrowing fibroblasts, and increased vascularization. Immunohistochemical stains demonstrated positivity for SMA, CD31, ERG, and CD34, highlighting prominent vascularization, while desmin, myogenin, myoglobin, STAT6, beta-catenin, S100, and AE1/AE3 were negative. Differential diagnosis included intravascular fasciitis, and possibly organizing thrombus with myxoid stroma. USP6 gene rearrangement (FISH) study was positive, confirming the diagnosis of nodular fasciitis. Results (if a Case Study enter NA) N/A Conclusion This case emphasizes the significance of maintaining a broad differential diagnosis when assessing specimens sent as thrombectomies. Recognizing intravascular nodular fasciitis as a potential presentation mimicking thrombosis is essential for accurate diagnosis and management.