Paralabral cyst of the shoulder with quadrangular space syndrome
Shoulder pain. Suspected labral injury.
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Increased signal of the inferior labrum is visible at 6 o'clock, in keeping with labral injury. A large, multiloculated cystic lesion is arising from that location and extending in the postero-inferior direction, protruding into the quadrangular space. Subtle edematous changes of the teres minor muscle are visible, without atrophy or fatty infiltration, which is consistent with acute denervation changes.
A large paralabral cyst compressing the axillary nerve is one of the causes of quadrangular space syndrome. Both the teres minor and the deltoid muscles are innervated by the axillary nerve, but can be affected to varying degrees due to anatomical variability in the nerve branches.
Acute denervation results in muscle edema, while chronic changes consist of muscle atrophy and fatty infiltration.