Magnetic Resonance Imaging of Paralabral Cysts
Magnetic Resonance Imaging of Paralabral Cysts
Abstracts & Commentary
Synopsis: Paralabral cysts are occasionally identified in the shoulder and hip. They are usually associated with adjacent labral tears. Two recent studies emphasize the use of MRI for identification of these cysts and the associated labral pathology. The second article about paralabral cysts in the shoulders cautions against using direct cyst aspiration as the sole treatment of this disorder.
Sources: Magee T, Hinson G. Association of paralabral cysts with acetabular disorders. AJR Am J Roentgenol 2000;174:1381-1384; Tung GA, et al. MR imaging and MR arthrography of paraglenoid labral cysts. AJR Am J Roentgenol 2000;174:1707-1715.
Tears of the acetabular labrum can cause hip pain. some orthopedists are now repairing these tears via an arthroscopic approach. Since this is a condition that can be treated, it is important to identify a labral tear when doing an MRI to evaluate hip pain. The paralabral cyst is an occasional finding seen in association with these labral tears and it can be well seen on MRI.
This retrospective study identified a subset of 13 patients who had paralabral cysts around the hip in a group of 87 patients who underwent MRI at their institution. MRI arthrography was not obtained in any of these studies. All patients had a history of remote hip trauma. No patients had developmental dysplasia of the hip. Three patients had degenerative changes in the hip joint on conventional radiographs. Cysts were located on the posterior aspect of the hip in eight patients and along the anterior aspect in five patients. One patient has a percutaneous aspiration of the cyst using sonography. That cyst reaccumulated fluid, as seen six months later on an MR arthrogram.
Surgery was performed on 10 of these hips and all were found to have labral tears. Magee and colleagues conclude that paralabral cysts have a high incidence of association with labral pathology and demonstration of a paralabral cyst on MRI is a useful indirect sign of acetabular labral disorders.
Paraglenoid cysts are a red flag on MRI, usually indicative of a neighboring glenoid labral tear, just as they are in the hip of an acetabular labral tear. These cysts can also cause nerve entrapment in the shoulder region. This investigation found 51 paraglenoid cysts on MRIs of the shoulder of 46 patients. MR arthrography was performed on five of the patients. One patient had cystography. Arthroscopic surgery was performed on 17 shoulders and four patients had percutaneous needle aspiration of the cysts.
Cysts were best seen on T2-weighted images where they were high signal intensity. Mean cyst diameter and volume were 2.2 cm and 2.8 cm3, respectively. Fifty-seven percent of cysts were located adjacent to the posterior labrum. Thirty-nine cysts were located in the right shoulder and 12 cysts in the left shoulder. Shoulder pain was the chief complaint in 40 (87%) of the patients. Twenty (43%) of the patients had a history of trauma.
On MR imaging and arthroscopy, a labral tear was identified in 27 and 15 patients, respectively. Eight cysts that caused compression neuropathy were large and located next to the posterior or inferior labrum. In four of five patients, MR arthrograms showed no intra-articular contrast material in the cyst. Cystograms showed no communication wit the glenohumeral joint space, and cyst aspiration resulted in temporary symptom relief; however, cysts recurred in three of four patients, including one case where the cyst had been injected with steroid.
Some cysts caused denervation changes in the distribution of the suprascapular nerve. One cyst, located along the inferior labrum, produced denervation of the axillary nerve with characteristic pathologic changes in the teres minor muscle. Tung and associates report that this is the first time to their knowledge that a paralabral cyst has been shown to cause axillary neuropathy. This has actually been reported before in one patient.1 It is of interest that denervation identified through electrodiagnostic studies was seen on MRI in all but two patients. Tung et al postulate that some of these may have been neuropraxic injuries with myelin damage but axonal sparing resulting in normal signal intensity in the muscle on MRI. This form of neuropathy contrasts with axonometric nerve injuries where axonal loss distal to the site of nerve injury and abnormal signal intensity appear in the affected muscles. The images were obtained with Fast spin echo T2-weighting. Tung et al also postulate that short tau inversion recovery (STIR) imaging, with its known hypersensitivity to edematous change, might have detected the denervation in the two patients without those changes on MRI.
Comment by Lynne S. Steinbach, MD
These retrospective studies reaffirm the knowledge that paralabral cysts are secondary findings associated with labral tears in the hip and the shoulder. The imaging findings of these studies have been published before.1-7 The strength of these papers is that there is surgical proof in a larger group of cases. It has been difficult for other authors to obtain good surgical correlation.
These cysts are analogous to the meniscal cysts of the knee. Synovial fluid is pushed through a fibrocartilage tear into the surrounding soft tissues. Identification of cysts in these locations should alert the imager to take a careful look at the adjacent fibrocartilaginous structures and to suggest the presence of a labral tear when the labrum has not been adequately imaged with high-resolution studies or MR arthrography. It is of interest that the larger cysts were the ones that tended to produce muscle denervation in the shoulder.
When symptomatic, paralabral cysts have been treated by percutaneous aspiration, steroid injection, arthroscopic decompression, or open excision. It is of interest that cysts recurred in three of the four patients who underwent percutaneous aspiration of the shoulder cysts and in the one patient who had her hip cyst aspirated. This is an argument for repairing the tear first and aspirating the cyst later if it is still present.
Only a few of the MR examinations in the shoulder study were MR arthrograms and there were no MR arthrograms performed in the hip study. Although para-labral cysts can be a marker of labral pathology, the message in this day and age should be that we need to try to diagnose labral tears with high-resolution studies and MR arthrography. When doing an arthrogram, one should make sure to include a T2-weighted or STIR sequence to identify the cyst, since contrast does not usually flow into these cysts.
References
1. Sanders TG, Tirman PF. Paralabral cyst: An unusual cause of quadrilateral space syndrome. Arthroscopy 1999;15:632-637.
2. Schnarkowski P, et al. Magnetic resonance imaging of labral cysts of the hip. Skeletal Radiol 1996;25:733-737.
3. Haller J, et al. Juxtaacetabular ganglionic (or synovial) cysts: CT and MR features. J Comput Assist Tomogr 1989;13:976-983.
4. Tirman PF, et al. Association of glenoid labral cysts with labral tears and glenohumeral instability: Radiologic findings and clinical significance. Radiology 1994;190:653-658.
5. Fritz RC, et al. Suprascapular nerve entrapment: Evaluation with MR imaging. Radiology 1992;182:437-444.
6. Moore TP, et al. Suprascapular nerve entrapment caused by supraglenoid cyst compression. J Shoulder Elbow Surg 1997;6:455-462.
7. Steiner E, et al. Ganglia and cysts around joints.Radiol Clin North Am 1996;34:395-425.
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