Intramuscular Cyst-Rotator cuff

The cause of intramuscular cysts is not entirely clear but may be similar to that of paralabral cysts in the shoulder and hip and parameniscal cysts in the knee. As in those other types of cysts, a defect in the surface of a rotator cuff tendon may allow fluid from the glenohumeral joint (or associated bursae) to enter the substance of the rotator cuff tendon and then dissect along the tendon fibers and intramuscular planes to form a cyst either within the sheath or within the substance of a muscle.