Range of normal and abnormal subacromial/subdeltoid bursa fluid

To determine the range of normal and abnormal subacromial/subdeltoid (SA/SD) bursa fluid.

Using a 1.5-T magnetic resonance (MR) imaging scanner, 2 observers evaluated coronal oblique T2-weighted, fast spin echo, fat-suppressed images of 71 persons (36 asymptomatic volunteers and 35 patients with full-thickness rotator cuff tears [RCTs]) for the 1) widest thickness of the SA/SD bursa; 2) medial extent of bursa from the acromioclavicular joint (ACJ); and 3) because patients were supine, whether fluid was in the posterior quarter, middle quarter, anterior quarter, or anterior-most quarter of the bursa.

The range of bursa thickness was 0 to 7 mm (mean = 1.3 mm, median = 2 mm) in normal bursas and 0 to 8 mm (mean = 3.3 mm, median = 3 mm; P < 0.05, t test) in RCTs. Only 2 volunteers exceeded 3 mm in bursa thickness. In volunteers, 36% had no fluid present, 61% had a small amount of fluid lateral to the ACJ, and 1 had fluid directly beneath the ACJ (P < 0.05). In RCT patients, 37% had fluid directly under the ACJ or medial to the ACJ. Only 1 patient with an RCT had no bursal fluid. In volunteers, most fluid was in the posterior quarter (53%) or middle quarter (22%) of the bursa, whereas in RCT patients, most fluid was located in the anterior quarter of the humerus or anterior to the humerus (89%; P < 0.05).

Normal SA/SD bursa fluid is rarely thicker than 2 mm and tends to be located posteriorly. An abnormal amount of fluid is present when the thickness exceeds 3 mm, fluid is present medial to the ACJ, and fluid is seen in the part of the bursa anterior to the humerus.