Imaging description

Small amounts of fluid are commonly identified in the tendon sheaths of extensor tendons (Figure 36.1), particularly the extensor carpi radialis brevis and longus. The characteristic finding of the intersection syndrome on MR imaging is peritendinous edema around the first and second extensor compartment tendons, extending proximally from the crossover point.

Importance

Although the cause is unknown, fluid within the extensor tendon sheaths should not be mistaken for tenosynovitis unless the amount of fluid is excessive.

Typical clinical scenario

Tenosynovitis is an inflammatory condition that is diagnosed by noting hyperintense fluid that distends a tendon sheath and surrounds the indwelling tendon (Figure 36.2). Intersection syndrome is an inflammatory process of the second extensor compartment tendons of the forearm, characterized by pain and swelling 4–8 cm proximal to Lister’s tubercle of the distal radius.

Differential diagnosis

The main differential diagnosis is de Quervain’s tenosynovitis, which is characterized by tendinopathy and stenosing tenosynovitis affecting the abductor pollicis longus and the extensor pollicis brevis tendons and sheath.

Teaching point

Small quantities of fluid in the extensor tendon sheaths may be normal and not indicative of tenosynovitis. MR imaging can perform an important role in establishing the diagnosis of intersection syndrome of the forearm.