Localized TGCT of the tendon sheath
localized TGCT of the tendon sheath is a benign condition, which occurs with a slightly increased predilection for females, is second only to the ganglion as a source of localized swelling in the hand and wrist.
It occurs less frequently (3%–10%) in the ankle and foot.
These nodular lesions usually occur in association with a tendon sheath (formerly called giant cell tumor of tendon sheath). Excision is curative and recurrences are rare.
TGCT exists in three forms: diffuse, localized, and localized TGCT of tendon sheath
• TGCT of joints and tendon sheaths: diffuse type, also called pigmented villonodular synovitis (PVNS); the entire synovium of an affected joint or tendon sheath is involved. It affects individuals in their 30s and 40s with equal sex distribution. Grossly, the synovium is red-brown to mottled orange-yellow and prolific with coarse villi, finer fronds, and diffuse nodularity resembling an Angora rug. It is almost always monoarticular. The most common locations include the knee (80%), hip (15%), and ankle. Swelling and effusion accompanied by moderate discomfort, decreased range of motion, and increased warmth to palpation are typical. Pain is frequently less than anticipated for the degree of swelling.
• Localized TGCT of the joint (also called benign giant cell synovioma or localized nodular synovitis): involves only a portion of a synovial surface in a joint and the lesion is often pedunculated. It presents with symptoms similar to a loose body. It tends not to be as darkly pigmented and has less villous proliferation than is seen in the diffuse form.
• Localized TGCT of the tendon sheath (also called giant cell tumor of tendon sheath or fibroxanthoma of tendon sheath) has been discussed in Question 2 earlier. Histologically, all three forms of villonodular synovitis are remarkably similar.
The etiology of TGCT is due to a translocation between chromosomes 1p13 and 2q35 in which the gene coding for colony-stimulating factor-1 (CSF-1), also called macrophage colony-stimulating factor 1, is fused to the collagen VI alpha-3 gene. Up to 15% of cells in the TGCT overexpress CSF-1. The remaining cells in the tumor are inflammatory cells recruited into the tumor because they contain the receptor for CSF-1.
What does the synovial fluid analysis reveal in the diffuse type of TGCT (PVNS)?
Typically, the fluid is brown or grossly hemorrhagic. This finding on joint aspiration should raise diffuse TGCT as a diagnostic consideration. However, up to 50% of patients will not have a hemorrhagic synovial fluid. Additionally, similar hemorrhagic fluid can be seen in trauma, Charcot joint, bleeding disorders, sickle cell disease, and Ehlers–Danlos syndrome.
What are the characteristic radiographic findings in a patient with the diffuse type of TGCT (PVNS)?
Plain radiographs are usually nonspecific, except for mild increased density of the soft tissue of the joint due to blood and hemosiderin deposits. The tumor may invade into the bone causing cysts or scalloped erosive changes with sclerotic borders with preserved joint space until late in the disease course. The erosive changes can mimic gout or tuberculosis. The MRI appearance of TGCT is diagnostic in most cases. Nodules with sufficient hemosiderin appear dark on both T1- and T2-weighted images. Characteristic blooming artifact can be seen on gradient-echo imaging sequences due to hemosiderin deposition.
Histologic characteristics of TGCT
Grossly, the synovium looks like a tan to red-brown “shaggy carpet.” Microscopically, TGCT is distinctive. It is characterized by a dense cellular infiltrate composed of synovial cell hyperplasia with surface and subsynovial invasion of mitotically active cells with eosinophilic cytoplasm. Other invading cells are fibroblasts, lipid-laden macrophages (xanthoma cells), hemosiderin-containing macrophages, and scattered, frequent, multinucleated giant cells. Although TGCT is locally aggressive, it rarely metastasizes.
How is TGCT treated?
Surgical treatment with complete synovectomy is standard either via open or arthroscopic approaches. Recurrences, particularly in diffuse type TGCT (PVNS), occur in 20% to 40%. Intraarticular installation of radioisotopes or low-dose external beam radiation is used in refractory cases. Total joint arthroplasty may be necessary for cure. In inoperable cases or where operation would be morbid, tyrosine kinsase inhibitors with activity against CSF-1 receptor and monoclonal antibodies targeting CSF-1 receptor may be useful.