Mass-Like Arthropathies - Clinical Tree

The articular disorders that will be discussed in this chapter, pigmented villonodular synovitis, synovial chondromatosis, and amyloidosis, share some common radiologic imaging characteristics. These entities are more common in large joints, the plain radiographic findings may be subtle, and the magnetic resonance (MR) findings are distinctive. Despite the fact that these conditions are relatively uncommon, most radiologists will see these diagnoses several times during a career and therefore must be well versed on their distinctive radiologic presentation.

Pigmented villodular synovitis

Pigmented villonodular synovitis (PVNS) is an uncommon neoplastic condition that arises in the synovium of joints, tendon sheaths, and bursae. It is a monoarticular disease with rare exception. The presentation in an affected joint or extremity may be focal or diffuse. The most common age at time of diagnosis ranges from 20 to 40 years, but this disease may be seen in children and older adults. The radiographic presentation of PVNS depends on whether the disease is extraarticular on intraarticular.

Extraarticular PVNS presents radiographically as a focal, noncalcified soft tissue mass in the hand and wrist (75%), followed by the foot or ankle. It is commonly known as giant cell tumor of the tendon sheath. The mass may cause scalloping or well-corticated erosion of adjacent bone ( Fig. 23-1 ).

Figure 23-1, Oblique view of the foot in giant cell tumor of the tendon sheath. There are well corticated erosions in the third and fourth tarsometatarsal (TMT) joint ( arrowheads ). Lytic lesion with sclerotic margins in the proximal third metatarsal is caused by intraosseous extension of tumor.

The intraarticular form of PVNS may be focal or diffuse. These patients usually present with complaints of pain or joint swelling. The focal intraarticular form of PVNS almost exclusively presents in the knee and will therefore have little radiographic changes ( Fig. 23-2 ).

Figure 23-2, Focal PVNS of the knee. A, Lateral view of the knee shows subtle soft tissue mass anterior to the distal femur ( arrows ). Sagittal T1-weighted ( B ) and fat-suppressed T2-weighted ( C ) images of the knee show focal mass anterior to the distal femur with characteristic low T2 signal of PVNS.

The diffuse intraarticular form of the disease has been described in virtually every joint but is most commonly seen in the knee followed by the hip, ankle, shoulder, and elbow in decreasing order of frequency.

The radiographic findings in diffuse intraarticular PVNS are as follows:

1.
Effusion
2.
Soft tissue swelling
3.
Preservation of joint space
4.
Maintenance of bone mineralization
5.
Well corticated extrinsic erosions in 50 percent of patients—usually seen where synovium is tightly applied to bone (i.e., neck of the femur in the hip, posterior femur, rim of medial and lateral tibial plateau in the knee)
6.
No calcification

The MR appearance of PVNS is distinctive regardless of the form of the disease. The classic presentation is that of a mass with heterogeneous low to intermediate signal on T1- and T2-weighted images ( Fig. 23-3 ). The extent of low signal is dependent on amount of hemosiderin in the lesion. The T2 low signal presentation of PVNS is distinctive; it is unfortunately not specific. Plain film radiography will help distinguish the low T2 signal from that occasionally seen in synovial chondromatosis, amyloid arthropathy, gout, or hemophilia.

Figure 23-3, Axial T1-weighted ( A ) and sagittal fat-suppressed T2-weighted ( B ) MR images of the knee in patient with diffuse PVNS. Low signal masses ( arrows ) extend from the joint into the surrounding soft tissues. There is erosion of the posterior distal femur ( arrowhead ).

Synovial chondromatosis

Synovial chondromatosis is a benign neoplastic disorder in which the synovium forms chondroid bodies. If and when these chondroids ossify, the diagnosis can be made from the plain radiograph ( Fig. 23-4 ). When they do not calcify, then one must proceed to MR imaging to make the diagnosis. Though synovial chondromatosis has been described in every location, the knee is most commonly affected, followed by the hip, elbow, shoulder, and ankle in descending order of frequency. It is most commonly seen in 20- to 40-year-old men. The most common radiographic findings are:

1.
Preserved joint space
2.
Normal mineralization
3.
Well-corticated erosions or scalloping of the adjacent bone in tight joints, which occurs in 30 percent of cases
4.
If chondroid bodies ossify, they are numerous, small, and uniform in size

Figure 23-4, A, Lateral view of the knee shows extensive small intraarticular calcifications that are typical of primary synovial chondromatosis. There is erosion of the posterior distal femur ( arrowhead ). B, Anteroposterior (AP) view of the hip in a different patient with synovial chondromatosis. Calcification is less prominent ( arrow ). There is a large, well-corticated erosion of the femoral neck ( arrowheads ).

Synovial chondromatosis is not to be confused with the chondral and osseous fragments seen in a patient with severe osteoarthritis. In this latter situation, not only are there changes of osteoarthritis, but also the calcified fragments seen vary in size and shape.

The MR image appearance of synovial chondromatosis is differentiated from PVNS on T2-weighted images. The unmineralized portions of synovial chondromatosis are intermediate to high in signal on fluid-sensitive sequences ( Fig. 23-5 ). Low signal on T2-weighted images, which can cause confusion with PVNS, is an indication of mineralization. However, then plain film will make the diagnosis clear ( Fig. 23-6 ).