What could be some possible reasons for a kidney to not show up on imaging?

Several factors.: Virtually all stones can be visualized by ct scanning, except for the very rare indinavir stone. Prior to the widespread use of ct, stones that do not show up on x-ray films were called radiolucent. Uric acid stones, for instance, do not appear on plain films. Very small stones may not show up, as well as matrix stones with little calcium content.