A Tenosynovial Giant Cell Tumor (TGCT) is a rare, slow-growing mass that affects the soft tissues around the joints and tendons. While it is classified as a benign, non-cancerous growth, TGCT is considered locally aggressive because of its potential to invade and damage the surrounding bone and cartilage. This tumor arises from the synovium, the specialized lining of joints and tendon sheaths, and can lead to significant pain, swelling, and reduced mobility if not addressed. Understanding the nature of this tumor and its distinct forms is the first step toward effective management.
Defining Tenosynovial Giant Cell Tumor
The anatomical origin of a Tenosynovial Giant Cell Tumor is the synovium, a thin membrane that lines the inner surface of joints and tendon sheaths. This lining produces the lubricating synovial fluid, which is essential for smooth joint movement. TGCTs develop when cells within this tissue begin to overgrow and proliferate, forming a tumor mass that can occur in any joint, bursa, or tendon sheath in the body.
The tumor’s cellular makeup includes large, multinucleated “osteoclast-like giant cells” mixed with smaller synovial-like cells and macrophages containing iron deposits (hemosiderin). This mixture results from a specific genetic anomaly causing the overproduction of Colony-Stimulating Factor 1 (CSF1). The excess CSF1 attracts CSF1-receptor-expressing macrophages, which accumulate to form the bulk of the tumor.
TGCTs are most frequently found in the extremities. The knee is the most commonly affected large joint, while the hands and fingers are the predominant sites in smaller joints, accounting for approximately 85% of cases. Other common sites include the hip, ankle, and elbow. The tumor’s growth mechanically interferes with joint function, often leading to chronic issues.
The Two Distinct Forms
TGCT is categorized into two distinct clinical forms that differ in growth pattern, prevalence, and recurrence potential. The localized form is the most common, while the diffuse form is more aggressive and challenging to treat.
Localized Form (L-TGCT)
The Localized Form (L-TGCT), formerly known as Giant Cell Tumor of the Tendon Sheath (GCTTS), accounts for the vast majority of TGCT cases. It presents as a well-defined, nodular mass, typically encapsulated and limited in size (0.5 to 4 centimeters). L-TGCT commonly develops around the tendon sheaths of the fingers and toes, growing slowly. Because it is circumscribed, it is less destructive to surrounding joint structures.
Diffuse Form (D-TGCT)
The Diffuse Form (D-TGCT), previously known as Pigmented Villonodular Synovitis (PVNS), is the rarer subtype. D-TGCT is locally aggressive and infiltrates the entire joint lining, often presenting as a large, ill-defined, intra-articular mass. This diffuse growth pattern makes complete surgical removal difficult, resulting in a high recurrence rate, estimated between 33% and 50%. This type most often affects large joints, involving the knee in up to 75% of cases, followed by the hip.
Recognizing Symptoms and Confirmation
Symptoms of a Tenosynovial Giant Cell Tumor often develop slowly. The most common signs include gradually progressing swelling, joint stiffness, and a reduction in the joint’s range of motion. Pain is often mild or intermittent, which can delay seeking medical attention.
Symptom presentation differs between the two forms. L-TGCT typically appears as a palpable, slow-growing lump, especially in the fingers, that may cause a catching or locking sensation. D-TGCT is more likely to cause joint effusion (fluid buildup) and is associated with more pronounced pain and joint destruction due to its widespread nature. Suspicion is often raised following unexplained, persistent joint swelling or the discovery of a non-tender mass.
Diagnosis relies on imaging studies, with Magnetic Resonance Imaging (MRI) being the essential tool. MRI clearly shows the extent of the tumor and its characteristic low-signal intensity, caused by hemosiderin deposits within the tumor. While imaging suggests the diagnosis, definitive confirmation requires a tissue sample. A biopsy allows pathologists to identify the characteristic multinucleated giant cells and other cellular components.
Management and Therapeutic Approaches
Surgery for complete tumor removal is the primary treatment for both forms of Tenosynovial Giant Cell Tumor. For the localized form, simple surgical excision is often curative, aiming to remove the well-defined mass with clean margins. This procedure is often performed arthroscopically using minimally invasive techniques, especially for smaller tumors.
The diffuse form presents a greater surgical challenge due to its infiltrating nature involving the entire joint lining. Surgeons must perform an extensive synovectomy to remove all affected tissue, often requiring a more involved open procedure. Despite meticulous surgery, the diffuse form has a high rate of local recurrence.
For recurrent or unresectable D-TGCT, non-surgical and adjuvant therapies are important considerations. Radiation therapy may be used in select cases to control tumor growth and reduce recurrence risk after surgery. Targeted molecular therapies, specifically Colony-Stimulating Factor 1 Receptor (CSF1R) inhibitors, are available. Medications like pexidartinib and vimseltinib target the tumor’s underlying genetic mechanism and are approved for advanced or symptomatic cases where surgery is not an option.