Diagnosis

Paralabral cyst associated with posterior labral tear

Findings

The radiographs were normal (Figure 1), showing no evidence of glenohumeral dislocation on the axillary view (not shown). The MR images revealed a posterosuperior labral tear with an adjacent, large paralabral cyst (Figure 2) that extended up into the area of the suprascapular notch (Figure 3), without evidence of supraspinatus or infraspinatus muscle atrophy.

Discussion

Paralabral cysts are relatively common incidental findings found on shoulder MR examinations. They indicate the presence of a nearby labral tear, although one is not always seen on MR imaging. It is believed that these cysts are formed following trauma to the capsulolabral complex, leading to extravasation of synovial fluid, which accumulates as either a unilocular or multilocular cystic structure. Paralabral cysts can be classified as synovial cysts, ganglion cysts, or pseudocysts. Synovial cysts occur through evagination of the joint capsule and contain a thin synovial cell lining. Ganglion cysts can arise from ligament, tendon, bone, joint capsule, or bursa; pseudocysts are fluid-filled structures within the soft tissues that lack the cellular lining of a true cyst. Paralabral cysts that occur in the suprascapular notch have been reported to cause entrapment neuropathies of the suprascapular nerve alone or both the suprascapular and infrascapular nerves.1 Impingement of the infrascapular nerve by itself can occur if the cyst is localized to the spinoglenoid notch.2 Larger cysts may impinge on the axillary nerve and result in teres minor denervation atrophy, but this is uncommon.3 Patients with paralabral cysts usually present with chronic, diffuse, and deep postero-lateral shoulder pain. Radiography will not demonstrate paralabral cysts or associated capsulolabral injuries. MR imaging findings include a thin-walled, rounded, sometimes multiloculated hyperintense structure on T2-weighted imaging that is hypointense on T1-weighted imaging. Detection of a paralabral cyst should always prompt a search for an associated labral tear. Electromyographic assessment and nerve conduction studies are helpful in determining the degree and site of nerve compression.2 The treatment of paralabral cysts has traditionally been performed by open surgery, but more recently, there has been success with arthroscopic cyst excision, with repair of any associated intra-articular pathology.4 In the absence of pain, these lesions can be treated conservatively with rehabilitation and a goal of optimizing shoulder function. Conclusion: Paralabral cysts are the sequelae of labral tears and can be detected using a fluid-sensitive MR imaging sequence. Identification of these structures can lead to prompt, appropriate treatment and the return of normal shoulder function. 1. Ianotti JP, Ramsey ML. Arthroscopic decompression of a ganglion cyst causing suprascapular nerve compression. Arthroscopy. 1996;12:739-745. 2. Wong P, Bertouch JV, Murrell AC, et al. An unusual cause of shoulder pain. Ann Rheum Dis. 1999;58:264-265. 3. Tung GA, Entzian D, Stern JB, et al. MR imaging and MR arthrography of paraglenoid labral cysts. AJR Am J Roentgenol. 2000;174:1707-1715. 4. Ferrick, MR, Marzo JM. Ganglion cyst of the shoulder associated with a glenoid labral tear and symptomatic glenohumeral instability. Am J Sports Med. 1997;25:717-719.