Quadrilateral space syndrome
Young woman with vague pain in the lateral shoulder.
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There is a 12x16x17 mm mass lesion located in the quadrilateral space. The signal characteristics are as follows: iso signal on T1W images, heterogenous signal on PD images, water signal in fluid sensitive images.
Note the increased signal in T2 fat suppressed sequence within the teres minor and deltoid muscles that is consistent with acute edema due to acute muscle denervation. Minor volume loss and fatty change however noted in the left deltoid muscle.
The quadrilateral space (a.k.a. quadrangular space) has the following borders:
- teres minor muscle superiorly
- long head of triceps muscle medially
- shaft of humerus laterally
- teres major muscle inferiorly
Two important anatomic structures in this space are axillary nerve and posterior circumflex humeral artery. Any mass lesions or fibrotic bands in this space may compromise these structures and cause symptoms.
The axillary nerve innervates teres minor and deltoid muscles. In this case, the early phase of denervation is represented as edema in this muscle group, which is more apparent on the fat sat images as high signal intensity in the muscles.