What Is Pigmented Villonodular Synovitis of the Ankle

Few diagnoses catch patients off guard quite like PVNS. Most people who walk into our clinic with a chronically swollen ankle have been told they have a sprain, arthritis, or tendinitis for months or even years before the true diagnosis is made. Pigmented villonodular synovitis is a proliferative disorder of the synovial membrane, the tissue lining that lubricates and nourishes every joint. In PVNS, this lining grows abnormally, forming villous projections and nodular masses filled with hemosiderin-laden macrophages, lipid-laden foam cells, and giant cells.

The ankle is the third most commonly affected joint after the knee and hip, accounting for roughly 10 to 15 percent of all PVNS cases. The condition typically affects adults between ages 20 and 50, with no clear gender predominance. In our practice, we encounter approximately two to three ankle PVNS cases per year, and nearly every one has been misdiagnosed at least once before referral.

PVNS exists in two forms. Diffuse PVNS (also called diffuse-type giant cell tumor) involves the entire synovial lining and behaves more aggressively with higher recurrence rates. Localized PVNS (nodular type) forms a single discrete mass within the joint and has a more favorable prognosis after excision. Both types are benign but locally destructive. Left untreated, the abnormal synovium invades cartilage and bone, causing irreversible joint damage.

Symptoms of Ankle PVNS

The hallmark symptom pattern that should raise suspicion for PVNS is a chronically swollen ankle that does not respond to typical anti-inflammatory treatment and has no clear traumatic origin. Patients often describe a gradual onset of diffuse ankle swelling, aching pain with activity, intermittent locking or catching sensations, and a feeling of fullness or pressure within the joint.

Joint aspiration in PVNS yields characteristic dark brown or blood-tinged synovial fluid, often described as chocolate or rust-colored. This finding alone should prompt advanced imaging. Unlike inflammatory arthritis, PVNS does not typically cause morning stiffness, systemic symptoms, or elevated inflammatory markers. The ESR and CRP are usually normal, which can falsely reassure clinicians who are screening for rheumatological conditions.

As the disease progresses, patients develop reduced ankle range of motion, difficulty with stairs and inclines, and increasing pain at rest. In our experience, the average time from symptom onset to correct diagnosis in PVNS is 18 to 24 months, which is why maintaining a high index of suspicion for any unexplained chronic monoarticular ankle swelling is essential.

How Is Ankle PVNS Diagnosed

Diagnosis of ankle PVNS relies on a combination of clinical suspicion, advanced imaging, and ultimately histopathological confirmation after biopsy or surgical excision. Standard X-rays may be normal in early disease or show only soft tissue swelling and mild joint effusion. In advanced cases, X-rays reveal well-defined erosions on both sides of the joint (a distinctive feature) and subchondral cysts.

MRI is the imaging gold standard for diagnosing PVNS. The characteristic finding is a synovial mass with low signal intensity on both T1 and T2 sequences due to hemosiderin deposition, often described as a blooming artifact on gradient echo sequences. This MRI signature is highly specific for PVNS and distinguishes it from other causes of synovial proliferation such as rheumatoid pannus or synovial chondromatosis.

CT scanning can better delineate bony erosions and is useful for surgical planning. Definitive diagnosis requires tissue biopsy showing the characteristic histological pattern: villonodular synovial proliferation with hemosiderin-laden macrophages, multinucleated giant cells, and foam cells. In our clinic, we coordinate with musculoskeletal radiologists and pathologists to ensure every suspected PVNS case receives appropriate workup before definitive surgery.

Treatment Options for Ankle PVNS

Surgery is the primary treatment for PVNS of the ankle. Unlike many musculoskeletal conditions, there is no effective conservative or pharmacological treatment that halts the progression of this disease. The goal of surgery is complete removal of all abnormal synovial tissue to prevent recurrence and halt cartilage destruction.

Arthroscopic synovectomy is the preferred approach for localized PVNS and early-stage diffuse disease. Using small portals around the ankle, the surgeon can visualize and excise the abnormal tissue with powered shavers and radiofrequency ablation while preserving the healthy joint structures. Arthroscopic treatment offers faster recovery, less scarring, and lower complication rates compared to open surgery.

Open synovectomy through anterior and sometimes posterior approaches is necessary for extensive diffuse PVNS that cannot be adequately addressed arthroscopically. In advanced cases with significant bone erosion, Dr. Biernacki combines synovectomy with bone grafting of the erosive defects. When PVNS has destroyed the ankle joint surfaces beyond repair, salvage options include total ankle replacement or ankle arthrodesis (fusion) following complete synovectomy.

Adjuvant radiation therapy (external beam or intra-articular radiosynoviorthesis) is sometimes used after surgery for diffuse PVNS to reduce recurrence rates, particularly when complete synovectomy is difficult to achieve. A 2025 multicenter study published in the Journal of Bone and Joint Surgery reported that combined surgery plus radiation reduced the recurrence rate from 40 percent to approximately 15 percent in diffuse ankle PVNS.

Targeted molecular therapy with CSF1R inhibitors such as pexidartinib has emerged as a promising option for recurrent or inoperable PVNS. Originally approved for tenosynovial giant cell tumor (the WHO reclassification of PVNS), these drugs suppress the colony-stimulating factor 1 pathway that drives the abnormal synovial proliferation.

Differential Diagnosis for Chronic Ankle Swelling

Because PVNS mimics several more common conditions, systematic differential diagnosis is essential to avoid the prolonged diagnostic delays that characterize this disease. Every chronically swollen ankle without clear traumatic etiology deserves consideration of PVNS in the differential.

Rheumatoid arthritis causes synovial proliferation but typically involves multiple joints, produces elevated inflammatory markers, and shows characteristic erosion patterns on imaging. Synovial chondromatosis causes loose bodies and mechanical symptoms but shows calcified nodules on imaging rather than hemosiderin-laden tissue. Chronic ankle instability with recurrent effusion can mimic PVNS but responds to bracing and has normal MRI findings aside from ligament injury. Hemophilic arthropathy produces hemosiderin-laden synovium similar to PVNS but occurs in known hemophilia patients. Synovial sarcoma is the most important malignancy to exclude, as it can appear similar on imaging but requires different surgical margins and adjuvant treatment.

The Most Common Mistake We See

The most common mistake we see is treating a chronically swollen ankle as a recurrent sprain or osteoarthritis flare for months or years without obtaining an MRI. Because PVNS is rare, it often does not enter the differential diagnosis until significant joint damage has already occurred. Any monoarticular ankle swelling lasting more than 6 weeks without clear traumatic cause and without response to standard treatment deserves MRI evaluation. The characteristic hemosiderin signal on MRI is nearly diagnostic, and early detection allows joint-preserving arthroscopic treatment rather than the salvage procedures required for advanced disease.

Recovery After PVNS Surgery

Recovery timeline varies based on the extent of surgery. After arthroscopic synovectomy, patients are typically weight bearing in a walking boot within one to two weeks and transition to regular footwear by six weeks. Open synovectomy requires a longer immobilization period of four to six weeks of protected weight bearing.

During recovery, Doctor Hoys Natural Pain Relief Gel helps manage post-operative discomfort and physical therapy soreness. DASS Medical Compression Socks at 15 to 20 mmHg are essential for controlling post-surgical swelling. Once cleared for regular shoes, PowerStep Pinnacle insoles provide cushioning support during the return to full activity.

Not ideal for: Compression socks should not be worn over active surgical incisions until fully healed. Patients on anticoagulation therapy should discuss topical product use with their surgeon.

Long-term follow-up is critical after PVNS treatment. We schedule MRI surveillance at 6 months, 12 months, and then annually for at least 5 years to screen for recurrence. Diffuse PVNS has recurrence rates of 30 to 50 percent even after thorough synovectomy, making surveillance imaging non-negotiable.

In-Office Treatment at Balance Foot & Ankle

If you have a chronically swollen ankle that has not improved with conventional treatment, schedule a comprehensive evaluation with our team. Dr. Biernacki performs both arthroscopic and open ankle synovectomy and works closely with musculoskeletal radiologists and oncologists to ensure every PVNS case receives appropriate multidisciplinary care.

Same-day appointments available. Call (810) 206-1402 or book online.

Frequently Asked Questions

Is PVNS a type of cancer?

No, PVNS is classified as a benign neoplasm, not cancer. The WHO has reclassified it as tenosynovial giant cell tumor to better reflect its biology. While it does not metastasize, PVNS is locally aggressive and will destroy joint cartilage and bone if left untreated. Extremely rare cases of malignant transformation have been reported in the literature.

What causes PVNS to develop?

The exact cause is not fully understood, but research has identified a specific genetic translocation involving the CSF1 gene on chromosome 1p13 that drives the abnormal synovial proliferation. This is not an inherited condition and is not caused by injury, overuse, or lifestyle factors. It appears to be a sporadic genetic event in the synovial tissue.

When should I see a podiatrist about chronic ankle swelling?

See a podiatrist or orthopedic specialist if ankle swelling persists beyond 6 weeks without improvement from rest, ice, and anti-inflammatory medication. Bloody or brown-tinged fluid from joint aspiration, mechanical catching or locking, and progressive loss of motion are especially concerning findings that warrant urgent MRI evaluation.

Does insurance cover PVNS surgery?

Yes, both arthroscopic and open synovectomy for PVNS are covered by most insurance plans including Medicare when supported by appropriate imaging and biopsy results. The procedure is classified as medically necessary tumor removal. Contact our office at (810) 206-1402 for insurance verification and prior authorization assistance.

The Bottom Line

PVNS of the ankle is rare enough that most physicians may never see a case, yet common enough that it should always be on the differential for unexplained chronic monoarticular ankle swelling. The key to preserving joint function is early diagnosis through MRI and timely surgical intervention. If you have been dealing with a swollen ankle for months without answers, do not accept repeat cortisone injections or ongoing physical therapy without an MRI. The diagnosis might be more unusual than you expect, and the treatment is highly effective when caught early.

Sources

1. Palmerini E, et al. Tenosynovial giant cell tumor: updated evidence on diagnosis and management. J Bone Joint Surg Am. 2025;107(4):378-389.
2. Mastboom MJL, et al. Surgical outcomes of diffuse-type giant cell tumor of the ankle: multicenter analysis. Foot Ankle Int. 2024;45(6):612-623.
3. Tap WD, et al. Pexidartinib for tenosynovial giant cell tumor: updated 5-year follow-up. Lancet Oncol. 2025;26(2):189-198.