Fluid around silicone implant. How should I interpret different results of MRI?

If the ultrasound shows a fluid collection, have the radiologist drain them! Another MRI could differentiate if it is fluid or implant. A good radiologist should be able to interpret the ultrasound and drain fluid collections.

I think you will receive the best information and advice from well experienced board-certified plastic surgeons (especially the surgeon who just operated on you) who have the opportunity to examine you AND evaluate the results of the imaging studies. In other words, in-person examination and correlation with the imaging studies will likely give you the  best chance of accurate diagnosis (and treatment options).   Best wishes.

Unfortunately, an MRI can
only provide a limited amount of information about what is causing your
anomalies, so it is important that you work closely with your surgeon, using
multiple tools, to determine exactly what is going on.An MRI, for instance, can detect the presence
of fluid, but not what the fluid is or what is causing it.So additional examinations and testing, and
potentially surgery, may be required to get to the root of the problem.