Case 20 Answer

Answer = Calcific bursitis. 

There is an unusual calcification just lateral and superior to the rotator cuff attachment on the greater tuberosity of the humerus. This calcification is smooth and mass like, conforming to the configuration of the lateral portion of the subacromial-SUBDELTOID bursa.

where is the bursa?  http://www.innerbody.com/image_skelfov/ligm10_new.html

This can be sue to several causes, including primary calcification of the bursa due to hydroxyapetite deposition disease, or HADD involving the rotator cuff that “spills” into the bursa or even chronic bursitis.

reference: http://www.learningradiology.com/archives2013/COW%20565-HADD/haddcorrect.html