Hi Jon,
You have to love predictive text when it does that to you,
Yes, I have seen exactly the same appearance on several occasions and have always wondered what they represent. Essentially it is exactly as you describe, a cyst within the bursa.
But I am not sure of the ethology. Is it a “ganglion” arising from the synovial lining of the bursa?
Whatever the ethology, I have seen these and depending on the location they may get caught under the CA ligament and cause some impingement.
I wonder if you popped a 22G needle into one and aspirated if it would disappear or if the contents is thick?
next time I see one I will suggest it to my radiologist !
Steve