The function of a healthy kidney is to remove naturally occurring and foreign toxins from the bloodstream and eject them from the body via urination. A healthy kidney is made up of three major structure: the cortex, the medulla, and the pelvis. The cortex is the largest part of the kidney, and makes up the entire outer area. This area is filled with capillaries that control the fluid interchange function of the kidneys; fluids that have had their toxins removed are passed through here in order to be reabsorbed back into the blood stream by the medulla.
Renal cortical hypoplasia is a disease in which the cortex of the kidneys is improperly developed. The natural result is that proper filtration of toxins from the bloodstream cannot be carried out and over time, renal failure is inevitable.
Renal cortical hypoplasia is diagnosed only after an extensive series of ultrasound and contrast radiographs. Even so, there are certain clinical signs that you can be on the lookout for if you suspect that your dog is suffering from this disease. This include an increased thirst and urination. This might seem counterintuitive - one might well ask why a dog with improperly functioning kidneys would urinate more rather than less. The answer is simply that the increased urination goes hand in hand with the increased thirst and even though more urine is passing out of the body, it's not carrying any of the toxins out of the bloodstream with it, so it is not indicative of a properly functioning kidney. In addition, lethargy and resistance to usual activity are common signs. Generally, a veterinarian will need to get both blood and urine samples to make a completely accurate diagnosis of renal cortical hypoplasia.
It's important to remember that there is no cure for renal cortical hypoplasia. It is a progressive disease that once started, will only get worse over time. There are plenty of steps you can take, however, to make your dog more comfortable during the duration of this disease. Firstly, giving him or her plenty of clean fresh water will help to prevent the common problem of dehydration. Ensuring that he or she gets ample exercise and attention will also forestall other complications such as obesity and depression that can quicken the onset of the disease. It's unlikely that your dog will readily go along with your attempts to exercise him or her, but in the end, the perseverance required is well worth it. Ultimately, however, it must be accepted that the disease is fatal and renal failure will eventually occur.
Renal cortical hypoplasia is a genetically inherited disease and so dogs that suffer from it or have close family members who do should not be used to breed.