Pigmented villonodular synovitis (PVNS) is a rare, slow-growing tumor that develops in the synovium, the thin tissue lining your joints. It affects roughly 1.8 per million people each year and causes the synovial lining to thicken and overgrow, gradually damaging the joint from the inside. The condition most commonly strikes the knee, hip, and ankle, and it tends to appear in adults between their late teens and late 30s. You may also see it called tenosynovial giant cell tumor (TGCT), which is the updated name adopted by the World Health Organization in 2020.
What Happens Inside the Joint
In a healthy joint, the synovium produces a small amount of fluid that lubricates the space between bones. In PVNS, a subset of synovial cells begins overproducing a signaling protein that attracts more and more immune cells into the joint lining. About 61% of cases involve a specific genetic rearrangement that drives this overproduction, while the remaining cases achieve the same result through other mechanisms. Either way, the outcome is identical: the synovium swells into thick, finger-like projections (villi) or solid nodules packed with inflammatory cells and iron-laden deposits called hemosiderin, which give the tissue its characteristic rust-brown color.
As the abnormal tissue expands, it erodes cartilage and bone. Repeated bleeding into the joint (hemarthrosis) accelerates the damage, leading to progressive stiffness and joint destruction if left untreated. PVNS is classified as a locally aggressive neoplasm, meaning it invades surrounding tissue but does not spread to distant organs.
Localized vs. Diffuse Types
PVNS comes in two distinct forms, and they behave quite differently.
The localized type appears as a single nodule inside the joint, sometimes resembling a loose body. It accounts for roughly a quarter of all cases and is most often found in the knee, ankle, or hand. The main symptom is painless swelling, and because it stays contained, it tends to cause less long-term damage.
The diffuse type is more common and more aggressive. Rather than forming one nodule, the entire synovial lining becomes diseased. It affects the knee in about 80% of cases, though the hip, ankle, shoulder, and wrist can also be involved. Symptoms are more severe: chronic pain, significant swelling, repeated episodes of blood collecting in the joint, and increasing difficulty moving the joint through its normal range. The diffuse form also infiltrates deeper into surrounding tissue, making it harder to remove completely.
Symptoms and Why Diagnosis Takes Time
PVNS is notoriously slow to diagnose. The tumor grows gradually, and early symptoms are vague. Most people first notice unexplained swelling in a single joint, sometimes without much pain at all. Because the onset is so insidious, symptoms are often present for years before anyone identifies the real cause. Many patients go through extensive workups for other conditions like rheumatoid arthritis or meniscal tears before PVNS is considered.
As the tumor enlarges, pain develops and worsens. The joint may feel stiff, lock during movement, or give way. Repeated bleeding episodes can make the joint warm and tender. Over time, range of motion becomes moderately to severely limited.
How PVNS Is Identified on Imaging
MRI is the most effective tool for diagnosing PVNS, and it produces a distinctive picture that experienced radiologists can often recognize immediately. The hemosiderin deposits scattered throughout the abnormal tissue create a characteristic low signal on most MRI sequences, appearing as dark areas within the thickened synovium. On a specific type of MRI sequence called gradient echo imaging, these iron deposits become even more conspicuous through what radiologists call a “blooming effect,” where the dark spots appear exaggerated and unmistakable.
This pattern helps distinguish PVNS from other causes of joint swelling, such as synovial chondromatosis or inflammatory arthritis. A biopsy of the synovial tissue confirms the diagnosis, revealing the hallmark mixture of giant cells, foam cells, and hemosiderin-laden cells.
Surgical Treatment
Surgery is the primary treatment for PVNS. The goal is to remove all of the abnormal synovial tissue, a procedure called synovectomy. This can be done arthroscopically (through small incisions using a camera) or through open surgery, and both approaches produce similar recurrence rates when the diseased tissue is fully removed.
Completeness of removal matters far more than the surgical approach. In one large series, 11 out of 13 patients who had a total synovectomy had good outcomes, compared to only 3 out of 9 who received a partial synovectomy. For hip PVNS without significant joint narrowing, synovectomy is the preferred approach, with recurrence rates ranging from 0% to about 8% for arthroscopic procedures and 0% to 20% for open surgery, depending on how extensively the disease has spread.
The localized form carries a much better prognosis after surgery. At five years, 73% of patients with localized disease remain recurrence-free, compared to just 48% of those with diffuse PVNS. That gap is apparent even at two years: 91% recurrence-free survival for localized disease versus 70% for diffuse. When diffuse PVNS does recur, repeat surgery or additional treatments may be needed.
Recovery After Surgery
Most people can bear full weight on the affected leg starting the first day after surgery, using a walker or crutches for support. The initial goal is getting out of bed and walking with an aid, then gradually regaining range of motion. Before leaving the hospital, you should be able to bend your knee to about 90 degrees. Once you can walk without a limp, the walking aid can typically be dropped.
Full recovery generally takes three to six months, though this varies depending on the extent of surgery and how much joint damage was present beforehand. Most patients return to normal work, sports, and daily activity within that timeframe. Long-term follow-up with periodic MRI scans is standard, particularly for the diffuse type, to catch any recurrence early.
Drug Therapy for Inoperable Cases
For patients whose tumors can’t be adequately removed with surgery, either because of the tumor’s location or because it has recurred repeatedly, a targeted medication called pexidartinib (brand name Turalio) has been available since its FDA approval in 2019. It works by blocking the receptor that drives the abnormal cell accumulation in the synovium. By interrupting this signaling pathway, the drug can shrink tumors and reduce symptoms in patients who have run out of surgical options.
Pexidartinib is specifically reserved for adults with symptomatic disease that causes severe functional limitations and isn’t expected to improve with surgery. It requires careful liver monitoring, and treatment continues until the disease progresses or side effects become unacceptable. Its availability marked an important shift for patients with advanced PVNS, offering the first non-surgical treatment that targets the underlying biology of the disease rather than just managing symptoms.