How to Read Your Shoulder MRI Report: Terms Explained

Shoulder MRI Views and Sequences

Shoulder MRI is acquired in three planes oriented to the shoulder joint (not the body). The coronal oblique view (aligned along the supraspinatus tendon) is the primary view for evaluating the rotator cuff. The sagittal oblique view shows the rotator cuff muscles in cross-section and is useful for assessing muscle atrophy and fatty infiltration. The axial view is essential for evaluating the labrum, glenohumeral ligaments, and subscapularis tendon.

T1-weighted images show anatomy with fat appearing bright. T2-weighted fat-saturated images highlight fluid, edema, and tendon pathology as bright signal. Some protocols include MR arthrography, where contrast is injected into the joint to better delineate labral tears and partial-thickness rotator cuff tears.

The Rotator Cuff

The rotator cuff consists of four tendons: supraspinatus (most commonly torn), infraspinatus, teres minor, and subscapularis. On coronal oblique images, the supraspinatus tendon appears as a dark band extending from the muscle belly to its insertion on the greater tuberosity of the humerus. A normal tendon is uniformly dark (low signal) with a smooth, convex superior surface.

Tendinopathy appears as thickening and intermediate signal within the tendon without a discrete defect. Partial-thickness tears show focal bright signal on T2 images that does not extend through the full tendon thickness. Full-thickness tears show bright fluid signal extending completely through the tendon, often with tendon retraction. For detailed grading systems, see our article on rotator cuff tear classification.

The Labrum

The glenoid labrum is a fibrocartilaginous ring that deepens the shallow glenoid socket and provides an attachment point for the glenohumeral ligaments and biceps tendon. On axial images, the labrum appears as a dark triangular structure at the rim of the glenoid. The anterior labrum is most commonly torn (Bankart lesion), typically from shoulder dislocations.

A labral tear appears as bright signal within or adjacent to the labrum, an irregular or blunted labral shape, or separation of the labrum from the glenoid rim. SLAP tears (Superior Labrum Anterior to Posterior) involve the superior labrum at the biceps anchor and are best seen on coronal oblique images. MR arthrography significantly improves labral tear detection.

Biceps Tendon, AC Joint, and Subacromial Space

The long head of the biceps tendon appears as a small, dark, round structure in the bicipital groove on axial images. Tendinopathy shows thickening and increased signal. The AC joint at the top of the shoulder commonly shows arthritis with osteophytes that can narrow the subacromial space and contribute to rotator cuff impingement. A hooked (Type III) acromion is associated with higher rates of rotator cuff tears.

Muscle Atrophy and Fatty Infiltration

When a rotator cuff tendon is torn, the associated muscle may undergo atrophy and fatty infiltration over time. These changes are best evaluated on sagittal oblique T1 images. The Goutallier classification grades fatty infiltration from 0 (no fat) to 4 (more fat than muscle). Advanced fatty infiltration (grades 3-4) is associated with poor outcomes after rotator cuff repair and may make the tear irreparable. For rehabilitation guidance, see our article on shoulder rotator cuff rehab.

Sources

1. Morag Y, Jacobson JA, Miller B, et al. MR imaging of rotator cuff injury: what the clinician needs to know. Radiographics. 2006;26(4):1045-1065.
2. Woertler K, Waldt S. MR imaging in sports-related glenohumeral instability. Eur Radiol. 2006;16(12):2622-2636.
3. Goutallier D, Postel JM, Bernageau J, et al. Fatty muscle degeneration in cuff ruptures. Pre- and postoperative evaluation by CT scan. Clin Orthop Relat Res. 1994;(304):78-83.
4. Expert Panel on Musculoskeletal Imaging; Amini B, Beckmann NM, et al. ACR Appropriateness Criteria Shoulder Pain-Traumatic. J Am Coll Radiol. 2018;15(5S):S171-S188.