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Pigmented Villonodular Synovitis (PVNS) is a rare, benign but locally aggressive proliferative disorder of the synovium, characterized by villous, nodular, or villonodular hyperplasia, hemosiderin deposition, and chronic inflammation. It can involve joints, tendon sheaths, or bursae.

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PVNS is now classified under Tenosynovial Giant Cell Tumors (TGCTs) by the WHO:
- Localized-type TGCT (previously nodular tenosynovitis).
- Diffuse-type TGCT (classic PVNS).

Epidemiology

Affects 20–50-year-olds.
Slight female predominance.
Incidence: ~1.8 cases per million/year.

Etiopathogenesis

Unclear etiology—proposed mechanisms include:
- Chronic inflammation.
- Trauma.
- Neoplastic process (CSF1 gene overexpression).
Leads to proliferation of synovial-like mononuclear cells, multinucleated giant cells, lipid-laden macrophages, and hemosiderin deposits.

Clinical Features

Chronic monoarticular joint swelling.
Pain, joint effusion, and stiffness.
Symptoms often wax and wane.
Mechanical symptoms: locking or clicking in some cases.
May mimic internal derangement or inflammatory arthritis.

![(A) Photo of right knee swelling. (B) Sagittal T2-weighted images illustrating a synovial lesion in the suprapatellar bursa. The arrow indicates scattered low-signal intensity areas in the villous hyperplastic synovium, representing hemosiderin deposits. (C) Sagittal T1-weighted fat-suppressed images illustrating bone erosion in the anterior aspect of the medial femoral condyle.

Liu Y, Liang S, Wang W. A rare case of long-term joint swelling caused by pigmented villonodular synovitis in a 3-year-old girl: a case report. Frontiers in Surgery. 2023;10. doi:https://doi.org/10.3389/fsurg.2023.1075171](attachment:8542c7c1-e149-40da-9698-49f68b64b17d:fsurg-10-1075171-g001.jpg)

(A) Photo of right knee swelling. (B) Sagittal T2-weighted images illustrating a synovial lesion in the suprapatellar bursa. The arrow indicates scattered low-signal intensity areas in the villous hyperplastic synovium, representing hemosiderin deposits. (C) Sagittal T1-weighted fat-suppressed images illustrating bone erosion in the anterior aspect of the medial femoral condyle.