Musculoskeletal Imaging

Tendon sheath

a partial or complete covering of synovial tissue over a tendon where it passes through fascial slings, osseofibrous tunnels and ligamentous bands. Among other functions, the tendon sheath promotes the gliding of tendons.

Inflammation of tendons sheaths, or tenosynovitis may occur in the synovial lining in rheumatoid arthritis and the seronegative spondyloarthropathy. Tenosynovitis is prominent on the dorsum of the hand, the fingers and the foot. In some cases, the tendon itself may become affected, leading to a variety of complications, including weakening, subluxation, entrapment and rupture.The most common radiographic finding associated with tenosynovitis and bursitis is soft tissue swelling; a sausage digit may be produced in some patients. Osteoporosis and surface erosion of subjacent bone can also be observed. Arthrography, bursography, tenography, and MR imaging are of value in delineating the nature of the soft tissue swelling.

Giant cell tumours may also arise from tendon sheaths, especially in the fingers and wrist. In some patients, deposition of haemosiderin or the presence of dense acellular fibrous tissue may lead to areas of low signal intensity on both T1-weighted and T2-weighted spin-echo MR images. At times these tumours may be confused with pigmented villonodular synovitis because of similar histologic features; tendon sheaths are sometimes involved as well as synovial membrane in villonodular synovitis.

The imaging assessment of tendon sheath abnormalities can be accomplished with various techniques. However, routine radiography and bone scintigraphy lack sensitivity, ultrasonography is applicable to analysis of only those tendons accessible to a probe placed on the skin, and tenography provides indirect evidence of tendon abnormality and requires a needle puncture. CT and MR imaging are the two techniques employed most commonly for evaluation of tendon sheaths (Fig.1) (Fig.2). The presence of small or even moderate amounts of fluid within a tendon sheath, by itself, is not diagnostic of an abnormality, as such fluid is seen in asymptomatic persons. About the ankle, tenosynovial fluid is more frequent in flexor tendons (as compared to extensor tendons) and is particularly prominent about the flexor hallucis longus tendon. However, the major MR imaging finding of tenosynovitis is abnormal accumulation of fluid within the tendon sheath. This fluid is of low signal intensity on T1-weighted spin-echo MR images and of high signal intensity on T2-weighted spin-echo images.

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Fig.2

Axial T2-weighted MR image of the wrist demonstrates fluid surrounding all tendons in the extensor compartments owing to tenosynovitis.
Tendon sheath, Fig.1 (a)
Tendon sheath, Fig.1 (b)
Tendon sheath, Fig.2