Basic anatomy of the shoulder by magnetic resonance imaging.

An understanding of the normal magnetic resonance (MR) infrastructural details of musculotendinous elements of the rotator cuff forms the basis for analysis of its pathology. The muscular bellies of the teres minor, infraspinatus, supraspinatus, and subscapularis are easily identified in MR images. In their lateral course both the supraspinatus and infraspinatus muscles transition to tendons gradually. Their lateral tendinous portions partially overlap and form a layered appearance on MR images. The subscapularis, with its fan-like tendinous insertional slips at the lesser tuberosity, can be identified easily in all imaging planes. The ligamentous structures of the shoulder, including the coracoacromial and coracohumeral ligaments, are visualized as low signal bands in all imaging planes. The capsuloligamentous structures including the superior, middle, and inferior glenohumeral ligament and glenoid labrum present considerable anatomic variations. This is especially true with respect to the anterior labrum, which varies from absent to a well-formed triangular appearance. Understanding the basic MRI anatomy of all soft tissue structures of the shoulder is essential for appropriate interpretation of lesions related to the shoulder.