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Case Report |
1
Department of Medical Imaging, Mount Sinai Hospital and the University Health
Network, 600 University Ave., Toronto, Ontario, M5G 1X5, Canada.
2
Department of Orthopedic Oncology, Mount Sinai Hospital, University of
Toronto, Ontario, M5G 1X5, Canada.
Received January 26, 2000;
accepted after revision March 6, 2000.
Address correspondence to L. M. White.
Introduction
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MR imaging (Signa 1.5-T scanner; General Electric Medical Systems, Milwaukee, WI) revealed a 4 x 3 cm mass adjacent to the inferoposterior glenoid labrum and extending into the quadrilateral space (Figs. 1A,1B,1C,1D). The mass showed low signal intensity on T1-weighted images and high signal intensity on T2-weighted images with a low-signal-intensity capsule (Figs. 1A and 1B). A neck was seen to extend through a cleft into the inferior glenoid labrum (Figs. 1B and 1C). The axillary nerve and the posterior humeral circumflex artery were stretched along the inferoposterior aspect of the mass (Fig. 1A). The teres minor and deltoid muscles appeared normal with no evidence of atrophy or signal changes consistent with denervation myopathy. The diagnosis was an inferoposterior glenoid cyst emanating from an inferior labral tear.
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At surgery a large glenoid labral cyst was seen occupying the quadrilateral space, with axillary nerve and vascular compression (Fig. 1E). The cyst was excised and the inferior labral tear oversewn. Pathologically, the specimen was shown to contain mucinous fluid and to have a fibrous cell lining consistent with that of a labral cyst. After surgery the patient regained normal sensation and pain-free abduction.
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Compartment compression syndromes associated with glenoid labral tears are most commonly seen with superior labral cysts involving the spinoglenoid notch [1]. In our patient, an inferoposterior labral cyst is described that resulted in a compartment syndrome of the quadrilateral space. The quadrilateral space lies inferoposteriorly to the glenohumeral joint with boundaries formed by the teres minor muscle (superiorly), the teres major muscle (inferiorly), the humerus (laterally), and the long head of triceps (medially). The space contains fat, the axillary nerve, and the posterior humeral circumflex artery. Cahill and Palmer [2] originally described the quadrilateral space syndrome in patients suffering from shoulder pain exacerbated by abduction and external rotation, paresthesia in a nondermatomal distribution, posterior point tenderness, and compression of the posterior humeral circumflex artery on abduction and external rotation of the arm. Symptoms are thought to occur as a result of compression of the axillary nerve, most commonly by oblique fibrous bands, although electromyography findings are frequently normal [2,3,4,5].
MR imaging in patients with quadrilateral syndrome usually shows no abnormality within the quadrilateral space but may reveal secondary features such as muscle atrophy [6]. Chronic axillary nerve compression eventually leads to atrophy of the teres minor and, less commonly, the deltoid muscles. The vascular imaging features of the syndrome are not specific and are typically illustrative of an extrinsic mass effect on the posterior humeral circumflex artery within the quadrilateral space [2,3,4, 7].
Because of the nonspecific nature of clinical and imaging tests, quadrilateral space syndrome is usually a diagnosis of exclusion. Surgical decompression of fibrous bands thought to originate from repeated microtrauma has proven successful in patients who do not respond to conservative therapy [2,3,4].
Other described cases of quadrilateral space syndrome include compression of the axillary nerve and posterior humeral circumflex artery as a result of soft-tissue hematoma (from a humeral fracture) and recurrent glenohumeral dislocation [2]. One other case report has described the quadrilateral space syndrome caused by an inferior labral cyst [8]. In that case the patient did not undergo surgery, and follow-up imaging showed resultant atrophy of the teres minor muscle. In our patient, the clinical course was relatively acute because of the large size of the cyst.
Differential considerations for soft-tissue lesions of homogenous decreased T1-weighted and increased T2-weighted signal intensities within the quadrilateral space also include a myxoid tumor or a cystic neurogenic lesion. As in our patient, diagnostic features of a labral cyst include these signal characteristics and identification of a communication with the labrum.
Because the suprascapular notch syndrome can be associated with superior labral tears, our case illustrates that inferior labral tears with an associated labral cyst can present with compression syndrome of the quadrilateral space.
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