In basic terms, feline plumbing consists of the kidneys, from which the ureters convey urine to the bladder, and the urethra, from which urine is discharged (hopefully into a litter tray).

Urethral obstruction causes dramatic clinical signs, as it means cats cannot urinate. Early signs may include straining to urinate, or frequent, unproductive visits to the litter tray. Loud vocalisation may accompany attempts to urinate.

Without prompt veterinary attention, affected cats may lose their appetite, become nauseous and vomit. The condition rapidly becomes life-threatening as toxins normally excreted in the urine build up in the blood stream.

Urethral obstruction is usually diagnosed by a veterinarian on the basis of a physical examination, and tends to manifest as a firm, painful, distended bladder.

In contrast, ureteral obstruction occurs higher upstream. If it only impacts one ureter, cats can still urinate.

Signs may be more subtle, and include back pain, reduced appetite and vomiting. In cases I have seen, owners report affected cats seem a bit "off colour", or "not themselves".

In a recent case I saw, the owners reported that their cat Neville had vomited three times, prompting them to make an appointment. He seemed a bit sore when picked up. But he seemed to perk up, so they almost cancelled.

Ureteral obstruction is not easily detected on physical examination. Ureters may be obstructed by crystals or stones in the urine, blood clots, strictures or even some cases of urinary tract infection. Diagnosis usually involves abdominal imaging (primarily ultrasound) and blood and urine tests.

In Neville's case, there were no obvious abnormalities on physical examination. But when blood and urine tests suggested that he had developed kidney disease, we performed an ultrasound to look closer at his urinary tract. It turned out that he had a tiny stone blocking one of his ureters.

Successful treatment usually requires surgery. The most common approach is the use of a device called a SUB (subcutaneous ureteral bypass). In other words, a tube is passed from the kidney, under the skin and then into the bladder, so that it bypasses the blocked ureter altogether. This procedure is performed by specialist veterinary surgeons.

The procedure is not without complications. These can include infection, and damage to kidney function.

Neville's owners proceeded with surgery, and to date, Neville and his SUB are doing well.

Previous studies suggest that male cats, those living exclusively indoors and some breeds like Persians and Himalayans are more prone to forming stones in their urine. Some of these stones may lodge in the ureters, causing ureteral obstruction.

In the past two decades, there has been an increase in the number of cases with ureteral obstruction, although we still don't know exactly why that is.

In order to determine potential risk factors for developing this condition, researchers at Sydney's Small Animal Specialist Hospital (SASH) reviewed the medical records of cats over the past three years diagnosed with ureteral obstruction.

They found that cats that ate a predominantly dry food diet were almost 16 times more likely to develop ureteral obstruction than those fed a predominantly wet diet.

There is ongoing research to isolate specific causes of ureteral obstruction and other forms of urinary tract disease in cats.

If you suspect that your cat is unwell, it's best to seek veterinary attention early.

Reference

KENNEDY, A. J. & WHITE, J. D. 2021. Feline ureteral obstruction: a case-control study of risk factors (2016-2019). Journal of Feline Medicine and Surgery, 1098612X211017461.

Dr Anne Quain BVSc (Hons), MANZCVS (Animal Welfare), Dip ECAWBM (AWSEL) is a lecturer at the Sydney School of Veterinary Science and a practising veterinarian.