What is the main differential diagnosis of an enchondroma?
A low-grade chondrosarcoma.
T1 hypointense, PD hyperintense lesion at the humeral head-neck junction (at the site of the former growth plate) measuring approximately 2 x 2 x 3 cm with a relatively narrow zone of transition and some intrinsic signal drop-out (due to calcifications, see CT for correlation). The lesion demonstrates vivid peripheral enhancement after IV contrast administration. Some central enhancement is noted due to translesional septae.
There is moderate tendinopathy of the supraspinatus tendon with thickening of the tendon and focal enhancement in keeping with chronic inflammation. Besides, a small bursal partial tear is noted with fluid in the lateral bursa. There is fluid along the long biceps tendon without interruption of the tendon itself.
The AC joint is thickened and demonstrates moderate enhancement. The subacromial space is narrowed. The other rotator cuff tendons are intact with some fluid along the subscapularis tendon. Mild to moderate subdeltoid and subacromial bursitis.
No fracture. Muscle bellys with normal volume. Type II acromion.
CONCLUSION: Subacromial impingement with bursitis and partial tear of the SSP tendon on the background of a chronic tendinopathy.
Incidental finding: Ovoid lesion at the head-neck junction of the proximal humerus with predominantly peripheral enhancement and a narrow zone of transition, in keeping with an enchondroma.