MR arthrography of the shoulder: variants and pitfalls.

Use of magnetic resonance arthrography to evaluate pathologic conditions of the shoulder is becoming widespread. However, normal anatomy or anatomic variations can cause interpretive errors. The most common variations occur at the origins of the glenohumeral ligaments (GHLs) and the insertion of the joint capsule. Among the GHL variants, common origin of the superior and middle ligaments is the most frequent followed by thinning, thickening, or absence of a ligament, most often the middle one. Absence or thinning of one ligament is sometimes associated with thickening of another or changes in the size and shape of the anterior capsular recesses. Common normal variants of the labrum include foramen sublabrum (detachment of the anterosuperior labrum from the glenoid margin) and the Buford complex (absence of the anterosuperior labrum in association with a thick middle GHL). Pitfalls related to the arthrographic technique include (a) visualization of a deep sulcus between the insertion of the long head of the biceps tendon and the superior labrum and (b) an apparent type III capsular insertion due to overdistention of the capsule by injected contrast material.