Re: Reliability of CT?
CT scans are pretty good but IMO, an MRI with and without contrast will show up better what is going on.
I would be very conservative about letting them do a needle biopsy, because there is a small but real chance that cancer cells, if present, could "seed" the needle track and spread.
Are you currently under the care of a kidney specialist, like a nephrologist; or seeing an oncologist? If not, my advice would be to search out a good one in your area for a consult soon, because they are used to reading the CTs and MRIs and might be able to tell you better what showed up, or at least be able to develop a plan for you as to what to do next.