Healthy kidneys are unremarkable in X-ray scans. In general, X-ray scans of the kidneys can provide information about changes in size, growths, calcium deposits in the kidney, positional changes, urinary stones or a change in the X-ray density of the kidneys.
Kidney function can also be assessed radiologically by administering the cat with X-ray contrast agent, for instance iohexol (as previously mentioned), via a vein and monitoring its elimination via the kidneys. If the contrast agent accumulates in the kidneys instead of being eliminated, this indicates that the kidneys have a reduced filtration capacity. It should be noted that the increased burden on the kidneys associated with eliminating the contrast agent may be counter-productive in advanced CKD. Careful consideration is, therefore, essential to decide whether this test is necessary.
Ultrasound examination of the kidneys allows more detailed changes to be investigated, some of which are not visible in X-ray images. These include cancerous changes, water retention, cysts and other structural changes in tissue and stones. Changes in the size and shape of the kidneys can also usually be clearly evaluated using ultrasound. Ultrasound is also helpful in diagnosing inflammation of the renal pelvis.
Computed tomography (CT) and magnetic resonance imaging (MRI)
These two techniques are being increasingly employed in veterinary medicine, despite their relatively high costs. In CKD cats, they are only employed to answer very specific questions and to clarify individual problems. This is partly due to the fact that they require cats to be anaesthetised. Anaesthetics are eliminated via the kidneys and carry the risk of weakening the cat. A decision on whether to employ such scanning techniques shouldn’t therefore be made solely on the basis of the costs involved.
X-ray, ultrasound, CT and MRI can help to identify abnormalities in the cat’s kidneys.