I'm sure it all depends on what angle the view is on the MRI. Dr. Shen noted there was a subtle change, but probably could not actually see what that was. I suspect that if you had repeat imaging, it would not be so subtle. There have been people here who have had abscesses defy all sorts of imaging and it was not until exploratory surgery that they were able to really see what was going on. Even with the EUA, they only "see" what is visible within their view, not what is going on inside.
I am so sorry that this just seems to be getting worse and worse. I wish I had something good to tell you. I guess the one good thing, is that this would explain why your symptoms are not the same as others with R/V fistulas. But, an explanation is not as good as finding out this is an easy-peasy issue, or even one that has a lot of documentation. I think you need to contact Dr. Shen and tell him that they may want a GYN specialist in on the EUA.
Jan