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Ganglia are common throughout the wrists and the hands. Many of these are overt and rarely require an imaging diagnosis. Ganglia around the wrist are an important cause of chronic central wrist pain. Large ganglia are easy to diagnose however small ganglia which can be equally symptomatic may escape clinical diagnosis. Ganglions can occur throughout the wrist and hand however at the wrist they most commonly arise as a consequence of degeneration of the scapholunate ligament.The aetiology is uncertain but mucoid degeneration in collagenous structures are felt to underlie most ganglia. Unlike synovial cysts, they do not have a cellular lining. Detection and diagnosis therefore depends on locating the scapholunate ligament, whether this is by ultrasound or MR. On MR, axial T2 weighted images with or without fat saturation are used. Axial images are followed until the radiocarpal joint is reached and then on one or two sections more distal to this the dorsal limb of the scapholunate ligament is identified. A section through the dorsal limb lies at approximately the level of the tip of the radial styloid. The ligament is easily identified as a low signal structure on most MR sequences. A ganglion cyst will be seen as a high signal T2 (fluid) mass lying adjacent to the ligament. On some occasions the ganglion may have a wide base abutting the ligament. In other cases, a serpigenous neck may extend away from the ligament, usually in a dorsal and radial direction. Even small lesions are considered significant however they can on occasion be difficult to differentiate from joint recesse
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Treatment On ultrasound a similar approach is taken. The proximal carpal row is identified by passing the probe in an axial plane from the distal radius towards the wrist joint. The transition between the “two bone” section representing the radius and the ulnar to the “three bone” section representing the scaphoid, lunate and triquetral is easily seen. Once this occurs, moving the probe slightly radially will identify the scapholunate articulation and the dorsal component of the scapholunate ligament is identified as a typical fibrillary ligamentous structure. The ligament can be dynamically assessed by gentle radial and ulnar deviation of the wrist. In some case of ligamentous incompetence, fluid can be seen flowing between the midcarpal and the radiocarpal joint on this manoeuvre. A ganglion if present is seen as an oval shaped echo poor structure abutting the ligament or, as described in the MR section, via a serpigenous neck which extends dorsally and radially. Ganglia can be differentiated from synovial recesses by the lack of compression. Ganglia arising on the volar aspect of the wrist are more difficult to detect unless they extend through the flexor tendons to a more superficial location. Ultrasound and MR imaging are important in these instances to detect occult lesions. Ultrasound has the additional advantage over MRI in allowing differentiation from a synovial recess, which can be compressed whereas ganglia can not. In addition, once a ganglion is identified on ultrasound, guided aspiration therapy is feasible. The contents of a ganglionic cyst are often viscus and sometimes patience is required to aspirate them completely. A small quantity of corticosteroid may be injected following aspiration although the precise efficacy of this is not established. Unfortunately ganglion cysts have a tendency to recur following aspiration.
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