PVNS

Pigmented villonodular synovitis (PVNS) is a rare, benign but locally aggressive proliferation of the synovium and related tendon sheaths. It is now commonly referred to as tenosynovial giant cell tumor (TGCT) and is categorized into a diffuse type, involving most of the synovium, and a localized type (nodular TGCT), presenting as discrete nodules in a tendon sheath, often in the fingers.

Most patients are adults in their 20s to 50s. The knee is the most commonly affected joint; other sites include the hip, ankle, and wrist. Diffuse PVNS typically causes chronic joint swelling, pain, and reduced range of motion, while the localized form usually presents as a solitary, slow-growing mass.

Pathogenesis is not fully understood, but a clonal translocation leading to overexpression of colony-stimulating factor 1 (CSF1) drives recruitment of macrophages and formation of pigmented, villous synovial tissue with hemosiderin deposits. Histology shows proliferative synovium with inflammatory cells, giant cells, and lipid-laden macrophages; CD68 positivity is common. MRI is the imaging modality of choice, with synovial proliferation and hemosiderin causing characteristic signal features and blooming on gradient-echo sequences. Radiographs may be normal early but can reveal bone erosions in advanced cases. Definitive diagnosis requires biopsy.

Treatment varies by type. Localized TGCT is typically managed with surgical excision of the nodules (arthroscopic or open). Diffuse TGCT often requires synovectomy; adjuvant radiotherapy is considered in selected cases. In adults, systemic therapy with CSF1 receptor inhibitors (for example, pexidartinib) is approved for TGCT with diffuse involvement and can reduce tumor burden, though liver toxicity requires monitoring. Recurrence is more common in diffuse disease, emphasizing the benefit of complete resection when feasible.