Hi, great question
Based on what you have reported, it is difficult to come up with concrete information. Sounds like your doctors do not yest know what is going on.
When a back MRI
is done, a scout film or localizer is acquired. A pelvic lesion was probably seen on this localizer or even on some of the other cuts. However, the back images are usually not accurate enough information to establish a diagnosis of a pelvic abnormality.
There are so many possibilities. Get the pelvic MRI and THEN from there start figuring out with your doctors what needs to be done.
Best of luck,,,