Kidney Stones (Uroliths/Nephroliths): Cat Kidney Disease Glossary

Kidney Stones, technically known as Nephroliths, are hard, rock-like mineral formations that develop within the renal pelvis (the collection funnel) of the kidney. While the general term for stones anywhere in the urinary tract is Urolithiasis, nephroliths are specifically located inside the kidney itself.

In the landscape of feline Chronic Kidney Disease (CKD), the most frequently encountered stone type is Calcium Oxalate. Unlike Struvite stones, which are often linked to infections and high urine pH, Calcium Oxalate stones thrive in acidic environments and are frequently associated with Hypercalcemia (high blood calcium), a common complication in CKD. Because these stones cannot be dissolved with special diets, they are permanent once formed.

The "Sleeping Giant" vs. The Emergency It is critical to distinguish between a stone that stays put and one that moves.

Non-Obstructive Nephroliths: Most kidney stones in cats remain "quiet" inside the kidney. They do not block urine flow and often cause no obvious pain. Veterinary consensus typically advises against surgically removing these stable stones, as cutting into a compromised kidney risks destroying more function than the stone itself is causing. They are simply monitored via X-rays.
Ureteral Obstruction (The Crisis): The true danger arises if a stone leaves the kidney and travels down the ureter (the tiny tube connecting the kidney to the bladder). Because a cat's ureter is incredibly narrow (often less than 0.4mm), even a grain of sand can get stuck. This causes a blockage that stops urine flow completely. The urine backs up into the kidney, causing it to swell massively (Hydronephrosis) and leading to rapid, fatal Acute Kidney Injury. This is often called "Big Kidney, Little Kidney" syndrome on physical exam: one kidney is huge and blocked, while the other is small and scarred from old CKD.

Treatment and the SUB System Since Calcium Oxalate stones cannot be dissolved, treatment for a blockage is mechanical. Standard surgery to cut the ureter is incredibly risky due to its small size and tendency to scar shut. Therefore, the modern gold standard for treatment is the Subcutaneous Ureteral Bypass (SUB) device. This involves surgically placing a generic "bypass tube" that connects the kidney directly to the bladder, skipping the blocked ureter entirely. This port sits under the skin and allows the kidney to drain freely, saving the organ from pressure necrosis.

Disclaimer: This content is for educational purposes only and does not constitute veterinary medical advice. Always consult with your primary care veterinarian or a veterinary internal medicine specialist regarding your cat’s specific condition.

The "Sleeping Giant" vs. The Emergency It is critical to distinguish between a stone that stays put and one that moves.

Non-Obstructive Nephroliths: Most kidney stones in cats remain "quiet" inside the kidney. They do not block urine flow and often cause no obvious pain. Veterinary consensus typically advises against surgically removing these stable stones, as cutting into a compromised kidney risks destroying more function than the stone itself is causing. They are simply monitored via X-rays.
Ureteral Obstruction (The Crisis): The true danger arises if a stone leaves the kidney and travels down the ureter (the tiny tube connecting the kidney to the bladder). Because a cat's ureter is incredibly narrow (often less than 0.4mm), even a grain of sand can get stuck. This causes a blockage that stops urine flow completely. The urine backs up into the kidney, causing it to swell massively (Hydronephrosis) and leading to rapid, fatal Acute Kidney Injury. This is often called "Big Kidney, Little Kidney" syndrome on physical exam: one kidney is huge and blocked, while the other is small and scarred from old CKD.