Diagnosis:
Grade II outlet related impingement with associated stenosis, more severe in the medial arch than the lateral arch, with severe AC joint proliferation, tendinobursitis, axillary or inferior labral chronic tear with parameniscal cyst. No evidence of rotator cuff tear.

Discussion:
There are several dramatic findings. First, in the sagittal projection Image 01 and coronal projection Image 04, there is severe hypertrophic change of the AC joint with pannus formation and callous formation (image 01a, image 04a). This is also seen on image 05 in the subacromial arch space anteriorly. Especially prominent is undersurface proliferation which produces arch stenosis (not impingement, but stenosis) narrowing the subacromial space. Also notice that the corocoacromial ligament is thickened anteriorly at its insertion on the acromion undersurface, especially on image 02, where the coracoacromial ligament insertion is labeled "A" (image 02a). Sagittal images, 02 and 03 demonstrate that the acromion slope is positive; in other words, the acromion slopes downward anteriorly, best appreciated on image 03.

The rotator cuff demonstrates slight increased signal in the T1 dataset, especially image 04 but it remains intact and becomes dark on the T2 dataset, image 07. This is a Grade I rotator cuff. It is tendonopathic. Now turn your attention to the montage coronal T1/T2 (image 11). Observe the peritendinous signal. The peritendinous bursal space is inflamed and demonstrates a white stripe (image 11a) that does not represent fat. You can confirm that this isn't fat by looking at the true T1 corresponding sister image in the montage. On the T1 dataset, this area will appear to be grayer. Several findings observed at surgery are also visible on the MR. A small labral tear was debrided.

This is best depicted in this particular patient in the coronal plane, where you may astutely discern a lobulated area of proteinaceous water signal intensity on image 08a and 09a. A small tail extends into the labral fissure and confirms the diagnosis of a parameniscal cyst. This tells you that you are dealing with a chronic anterior inferior instability process with a small labral tear that is long-standing which has led to a menical cyst. This is analogous to the meniscus tear and meniscal cyst in the knee. Without that cyst, the diagnosis of a small labral tear would have been difficult in the axial projection. Notice on image 10, an additional T1 coronal image that the axillary labrum appears to be shifted slightly towards the humerus, forming a "step-off". It is from the cleft of the axillary labrum and the bony glenoid that the small parameniscal cyst emanates.

The T-2 hyperintense cyst in this case was clearly closely associated with the labrum, thus was not a diagnostic dilemma. Otherwise, a listing of Common and Uncommon Water Signal Masses About the Shoulder is listed for your perusal.

Differential Diagnosis:
Primary concerns in a 44 year old with this history are acute injury to the cuff or labrum with or without dislocation vs. exacerbation of a chronic underlying problem. We do see evidence of chronic anterior/inferior instability (the labral parameniscal cyst) but no Hill-Sachs lesion or equivalent that would suggest prior dislocation. We also do not see evidence of direct impaction injury to the humerus, but this is also a finding we search for.