Clinical History: A 53-year-old male presents with chronic shoulder pain and clinically apparent deltoid atrophy. Coronal T1-weighted (1A) and fat-suppressed proton density-weighted (1B), coronal T1-weighted (1C), and sagittal T2- weighted (1D), and axial fat-suppressed proton density-weighted (1E) images are provided. What are the imaging findings? What is your diagnosis?
Note the chronic post-traumatic deformity of the inferior glenoid associated with thickening and scarring of the axillary pouch component of the inferior glenohumeral ligament (red arrow). The patient had concomitant rotator cuff disease with a deep bursal surface partial tear (white arrow) and a tear of the superior labrum (white arrowhead). A more posterior coronal T1-weighted (2C) image demonstrates marked posterior deltoid (red arrowheads) and teres minor (short black arrows) fatty atrophy indicating chronic denervation change of the axillary nerve (more than one atrophied muscle sharing the same innervation). A sagittal T2- weighted (2D) image shows the cyst (asterisk) inferior to the inferior glenoid and labrocapsular structures with a serpiginous connecting stalk (short red arrow). Note the marked fatty atrophy of the deltoid muscle (red arrowheads). The axial fat-suppressed proton density-weighted (2E) image reveals the cyst projecting into the quadrilateral space (asterisk), which is bounded superiorly by the teres minor, inferiorly by the teres major, medially by the long head of the triceps, and laterally by the humeral shaft. It contains the axillary nerve and posterior humeral circumflex artery.
Labral cyst compressing the axillary nerve within the quadrilateral space with resultant chronic axillary neuropathy.
Cysts around and within the shoulder most commonly arise from a tear of the labrum or shoulder capsule.1,2,3,4,5,6,7,8,9,10,11 Cysts found adjacent to the glenoid labrum have been shown to arise from a tear of the labrum in most cases.1,4,8 The tear is most commonly the result of acute trauma or repetitive motion (chronic microtrauma) injury.12 Tendon or intramuscular cysts may develop after a delaminating rotator cuff tear, typically articular surface or full thickness associated with a tear of the adjacent adherent capsule.13,14
The histologic characterization of labral cysts is debated as cystic lesions near the glenohumeral joint have been described by various authors as “ganglion cysts”15,16. 1981;(63):492–4.],17 “ganglia”18,19,20, “synovial cysts”21 and pseudocysts.4,22 A synovial cyst is lined by synovial cells and forms from evagination of the joint capsule or para-articular bursa.10 A ganglion cyst may arise from a joint capsule, bursa, ligament, tendon, or subchondral bone. A pseudocyst may result from the extrusion of joint fluid through a labrocapsular tear into adjacent soft tissues, and the pseudocyst pathogenesis has been likened to that of a meniscal cyst.4,23,24 To add to the confusion, the definition of a synovial cyst is controversial with some authors using the term synonymously with “ganglion,” whereas others define synovial cysts as herniations of the synovial membrane through the capsule of a joint filled by synovial fluid, which may or may not keep a communication with the joint.25,26,27,28 Synovial cysts are thought to serve as drainage reservoirs for excessive joint effusion in the setting of any arthropathy, escaping from its regular location through a one-way-valve mechanism into the area of least resistance.29. 2016;7(2):179–86. Available from: https://doi.org/10.1007/s13244-016-0463-z] Ganglion cysts lack a synovial cell lining and are constituted by a dense collagenous capsule surrounding a mucopolysaccharide-rich gelatinous fluid25,26,27,28,29,30, like that of a synovial cyst but at a higher concentration.25,29 A developmental continuum between a true synovial cyst and ganglion cyst of a synovial herniation followed by myxoid degeneration has even been theorized, but is presently not confirmed.25,29,30 Finally, a pseudocyst is lined by fibrous tissue, not synovial membrane, and is filled with mucoid content.22
A cyst may form from a labral tear and remain small and localized. Small cysts are commonly located posteriorly and anteriorly, possibly due to the confining adjacent muscles. Small cysts may remain small, especially if the labral tear heals. The cyst may spontaneously resolve, also possibly due to healing of the labral tear.31 The cysts can enlarge, sometimes reaching a size of multiple centimeters. The most common locations for larger labral cysts can be explained by the specific regional anatomy of the shoulder joint (Figure 3). The most frequent location of larger cysts is the posterosuperior aspect of the joint which can be accounted for by the fact that the posterosuperior capsule above the posterior band of the inferior glenohumeral ligament is an area of relative weakness when compared with the thicker anterior capsule.32 This weakness may allow easier penetration by dissecting fluid. Once a cyst forms, it expands through the path of least resistance into the fibro-fatty tissue that lies between the supraspinatus and infraspinatus muscle bellies in the posterior superior quadrant. This channels cysts that originate from posterosuperior labral tears toward the spinoglenoid notch and the suprascapular notch. An alternative posterior pathway is along the gutter formed by the bony glenoid, the fibro-cartilaginous glenoid labrum, and the origin of the infraspinatus muscle, which may explain why pure posterior tears (reverse Bankart lesions) may channel superiorly and then medially between the 2 muscle bellies similar to those cysts seen with posterior superior tears or posterior extension of superior labral tears (SLAP lesions). The anterior superior path of least resistance is the recess between the labrum and anterior capsule projecting into the subscapularis recess often associated with the anterior aspect of a SLAP lesion (Figure 3). A common pathway for cyst extension often associated with a chronic Bankart lesion below the subscapularis tendon is anteriorly and inferiorly into the quadrilateral space as in the test case.
Cysts around the shoulder joint have been termed labral cyst, paralabral cyst, ganglion cyst, synovial cyst, pseudocyst, and intramuscular and intratendinous cysts.4,13,14,27,29,33 Cysts in this discussion will be termed labral cysts when arising from the labrum and intratendinous or intramuscular cysts when arising from a rotator cuff tear if localized to the tendon (intratendinous) or into the muscle belly (intramuscular). Labral cyst is preferred when the cystic lesion is seen adjacent to the labrum, as this term emphasizes the important anatomic features of the lesion, rather than the variably defined terms ganglion and synovial cyst that describe the histologic appearance of the cyst wall.
A labral cyst of the shoulder joint is present in 2-4% of the general population, particularly in males during the 3rd and 4th decade.8 The cyst may be asymptomatic, be associated with nonspecific shoulder pain often in association with glenohumeral arthrosis, may be associated with clinical glenohumeral instability and/or in association with compression neuropathy.4 Instability of the shoulder should be clinically suspected and evaluated for when a cyst is found with an anterior inferior (Bankart), posterior (reverse Bankart), posterior superior (often posterior extension of a SLAP lesion), or superior labral tear (SLAP lesion). If the cyst is large enough, it may dissect into the suprascapular or spinoglenoid notch (or both) to impinge upon the suprascapular nerve or the quadrilateral space to impinge upon the axillary nerve. In the case of nerve impingement, the patient may present with pain, muscle weakness, and resulting loss of proprioception. In the case of suprascapular denervation there will be weakness of the muscles innervated (supraspinatus and infraspinatus). In the case of compression neuropathy of the axillary nerve within the quadrilateral space, there will be weakness of the deltoid and teres minor muscles (Table 1).
Shoulder cysts are decreased in signal intensity on TI-weighted images and of increased signal intensity on T2- or T2*-weighted images.1,2,4,34 The cysts can be unilocular (Figure 5), multilocular (Figure 6), rounded or oval-shaped, variably lobulated, and frequently located adjacent to a tear of the fibrocartilaginous glenoid labrum (Figure 7).1,4,29,34 Associated glenoid labral tears are characterized by areas of linear or complex increased signal intensity extending through the labrum on TI- weighted and GRE images, less intense high signal or fluid signal on T2-weighted images (Figure 7), or may be filled with contrast at MRI arthrography.
Healed labral tears may not demonstrate contrast filling but still exhibit the findings of a non-fluid filled labral tear. The area of abnormal signal intensity in the labrum may be in contact with or connected to a portion of the cyst.1,4,29 An MRI arthrogram may (Figure 8) or may not (Figure 9) show contrast material extending from the shoulder joint into a cyst via a labral tear. As some patent labral tears may not be fluid filled, MRI (or CT) arthrography may be necessary to help prove patency (Figure 8).
Similarly intratendinous and/or intramuscular cysts will exhibit the same MRI findings of a labral cyst except that the cyst is often away from the joint within the tendon or muscle (or both) and is not associated with the labrum. Intratendinous or muscular cysts tend to be associated with delaminating rotator cuff tears13,14 and often appear elongated (Figure 10). The connection to the articular surface or full thickness rotator cuff tendon tear may be patent (Figure 11) or closed (Figure 12). Cysts with patent communication may fill with contrast in the case of CT or MRI arthrography, thus proving patency whether the communication with the joint is directly visualized or not visualized (Figure 11).
Cysts and associated labral tears are frequently found with posttraumatic changes of the glenoid because of a traumatic etiology of the labral tear. Posttraumatic changes can include subchondral cyst formation from posttraumatic arthrosis, intraosseous extension of the labral cyst, or both (Figure 13).
Administration of intravenous gadolinium may show smooth rim enhancement of a cyst without internal enhancement. Pericystic enhancement may occur including within a labral tear as a result of hyperemia, possibly inflammatory mediated. (Figure 14).
Differential diagnostic possibilities can be split into imaging and clinical differentials. Imaging differential diagnostic possibilities include any cystic mass originating outside of the joint and include cysts originating from the AC joint typically associated with AC joint arthrosis as a result from previous trauma or a cyst that forms superior to the AC joint as a result of a defect in the acromioclavicular joint ligaments in association with long standing subacromial subdeltoid bursitis, also referred to as the geyser sign.27,34 Other diagnostic possibilities include cystic masses arising from trauma such as a hematoma acutely or sub-acutely or serous collections, including a degloving lesion from trauma or seroma from prior trauma or surgery. Varices arising in the venous plexus normally found in the spinoglenoid notch can enlarge, appear as a cystic mass and can be associated with suprascapular nerve denervation.35,36 Finally, cystic neoplasm may mimic a labral cyst. Clinically the differential diagnostic possibilities are varied and extensive as the cyst can be asymptomatic or symptomatic and associated with glenohumeral instability in the case of an associated labral tear or denervation in the case of nerve compression associated with a larger cyst or both. Any suprascapular or axillary denervation presentation that occurs without a cyst present can have a similar clinical presentation and therefore is in the differential diagnosis. Shoulder pain from a wide variety of causes are typically not associated with a cyst (Table 2) but can be associated and are therefore in the list of differential diagnostic possibilities.37
Treatment of labral cysts includes repair of the associated labral tear with or without drainage of the cyst.3,6,8,38,39 Cyst aspiration alone has been performed with recurrences reported4 and the general consensus is to treat the causative labral tear in order to prevent recurrence.3,6,8,38,39 In the case of compression neuropathy, current recommendations are to decompress the cyst and repair the labrum (often a SLAP lesion or posterior superior labral tear).3,9,39 There is a relative paucity of reports of treatment of intratendinous and/or intramuscular cysts and in general cyst decompression may be accomplished at the time of rotator cuff repair. Many cysts are incidental and may be treated conservatively if found in a patient that is not a good candidate for rotator cuff surgery.
Cysts around and within the shoulder most commonly arise from a tear of the labrum or shoulder capsule and can occur in up to 4% of patients, (possibly higher) presenting for MRI with shoulder pain. The clinical presentation varies and the cysts can be asymptomatic or be painful in the setting of instability with a labral tear. The cyst may also be associated with pain in the case of an intratendinous and/or intramuscular cyst associated with a rotator cuff tear. Larger labral cysts in the posterior superior quadrant can compress the suprascapular nerve and cysts in the anterior inferior quadrant can compress the axillary nerve and cause neuropathy. MRI is an excellent modality to demonstrate cysts, labral tears, and compression neuropathy, as well as associated findings related to chronic instability. MRI arthrography can demonstrate patency of an associated labral or rotator cuff tendon tear by filling of the cyst with contrast. The results of MRI or MRI arthrography aid in the clinical management of a patient with a cyst about the shoulder.
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- Shon MS, Jung SW, Kim JW, Yoo JC. Arthroscopic all-intra-articular decompression and labral repair of paralabral cyst in the shoulder. J Shoulder Elbow Surg. 2015;24(1). ↩
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