Thursday, October 6, 2011

Intramuscular Cysts of the Rotator Cuff

An intramuscular cyst of the rotator cuff is a secondary sign of rotator cuff injury that should prompt a careful search for a tendon tear. Interestingly, the torn tendon is not necessarily that of the muscle with the cyst. About 50% of rotator cuff tears associated with these cysts are partial-thickness.

Intramuscular cysts are most commonly found in infraspinatus and supraspinatus muscles, followed by the subscapularis and teres minor muscles. Cysts can also be seen in two different muscles.

It is thought that tendon defects from a tear allow joint or bursal fluid to track along the tendon fibers and intramuscular planes to form the intramuscular cyst. The problem with this theory is that the cysts are not always associated with tendon tears. Indeed, Manvar and colleagues found that ~25% of these cysts were not associated with rotator cuff tears on conventional MRI.

The images above reveal a cyst (white arrow) within the supraspinatus muscle associated with a tear (pink arrow) of the supraspinatus tendon.


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