A urethral stricture is scar tissue or tumour narrowing the tube that carries urine out of the bladder, and it behaves differently from the plug-and-stone blockage most owners have heard about. Flow drops to a thin stream instead of stopping dead, the cat strains for weeks instead of hours, and the bladder stays partly full. Three causes cover nearly every case: a scar after trauma or catheterisation, stones and inflammatory debris, and tumour or congenital narrowing. The 6-hour line is the safety rule: a cat that has produced no urine for 6 hours is an emergency, whatever the underlying cause turns out to be.
Stricture versus blockage
In a blockage, something fills the lumen: a struvite plug, a 1-3 mm stone, or a blood clot. In a stricture, the wall itself is narrower, often down to 0.5-1.5 mm across a segment 2-10 mm long. A blocked cat stops producing urine within hours. A strictured cat may dribble a 1-2 mm stream for weeks, urinate in 6-8 small spots around the house, and still empty half its bladder. That slow pattern is why strictures get missed until the cat has lost 10% of its body weight.
A 4 kg cat makes roughly 100-200 ml of urine a day. If you count 2 or 3 teaspoons in the box over 24 hours, that is under 10% of normal output, and the cat is obstructed in practice even if a trickle is coming out.
The 6-hour line, and what happens after it
Zero urine for 6 hours means go now. Between 6 and 12 hours the bladder becomes firm and painful, the cat stops eating, and vomiting usually starts. By 12-24 hours potassium climbs, the heart rate drops below 140 beats per minute, and the cat becomes hypothermic and depressed. Past 24 hours, collapse is the expected course. This is not a watch-overnight problem, and it is not something to manage with extra water and a warm bed.
Two situations are just as urgent without a full 6 hours. A cat that has been straining for 20 minutes with nothing produced, and a cat with a bladder that feels like a 3-4 cm firm ball on palpation. Both go to the clinic immediately. The full sign list is at /health/urinary-blockage-signs/, and it is worth reading before you need it.
Cause 1: scar after trauma or catheterisation
This is the most common structural cause in cats that have been catheterised. The catheter rubs the mucosa, inflammation heals into fibrous tissue, and the narrowing appears 2-8 weeks after the event. It usually sits in the penile urethra, 5-15 mm behind the tip, and it is 2-10 mm long. Risk rises with each catheter pass: 1 uncomplicated pass is low risk, 3 or more passes in a week, or a catheter left in place over 48 hours, clearly raises it. Pelvic fractures and dog bites cause the same scar through direct trauma.
The tell is timing. A cat that was urinating normally, blocked once, was unblocked, and then developed a thin stream 3-6 weeks later has a scar, not a new plug.
Cause 2: stones, plugs, and inflammatory swelling
Struvite and calcium oxalate stones 1-5 mm across lodge in the penile urethra, and the mucosa around them swells. The stricture here is partly mechanical and partly inflammatory, so it can improve when the stone passes or dissolves and return with the next episode. Chronic urethritis from feline lower urinary tract disease thickens the wall in the same segment. These cats often have a history of 2-4 episodes of straining in a year, each resolving in 24-72 hours.
Distinguishing this from scar tissue matters because the treatment differs: stone cases may need a diet change and a recheck in 4 weeks, while a scar needs mechanical widening.
Cause 3: tumour or congenital narrowing
Transitional cell carcinoma of the urethra and bladder neck narrows the lumen from outside as well as inside, usually in cats 8-12 years old, and comes with weight loss over 8 weeks and blood at the end of the urine stream. Congenital narrowing, including urethral hypoplasia and persistent penile frenulum, shows up in cats under 2 years, often as a kitten that has always dribbled and always licked its penis. Both need imaging rather than another course of antibiotics.
Three causes compared
| Cause | Narrowed segment (mm) | Typical age (years) | Imaging time (minutes) | Act within (hours) |
|---|---|---|---|---|
| Post-catheter scar | 2-10 | 3-8 | 20 | 24 |
| Stone or inflammatory plug | 1-5 | 2-6 | 15 | 6 |
| Tumour | 5-20 | 8-12 | 30 | 72 |
| Congenital narrowing | 3-12 | 0-2 | 25 | 72 |
The segment length drives the plan. A 2-4 mm scar can be dilated or cut in 1 session; a 10 mm or longer segment usually needs a stent or a reconstruction.
How the narrowing gets measured
Palpation tells you the bladder is full, not where the narrow part is. The useful tests are a contrast urethrogram, which shows the lumen as a fine 1-2 mm thread at the stricture, and ultrasound, which measures the wall thickness and the bladder volume in 5-10 minutes. Cystoscopy under anaesthesia gives the exact length and lets the surgeon decide between balloon dilation, a 2-4 mm incision, or a stent. Blood work comes first in any obstructed cat, because potassium and creatinine change the anaesthetic plan. Expect $300-$600 for imaging and $120-$250 for the panel; the /tools/cost/ page compares that with the rest of a workup.
What treatment actually changes
Balloon dilation stretches the scar to 3-5 mm and buys time, but roughly half of cats narrow again within 6-12 months. A urethral stent holds 6-8 mm open and is placed in 1 procedure; it changes the cat's stream permanently and raises the risk of urinary infection, so urine checks run every 3-4 months. Perineal urethrostomy creates a wider opening from the penile urethra and is the surgical answer for a scar that keeps returning. None of these is an emergency-room decision made in 10 minutes; the emergency is stabilising the cat, and the reconstruction is planned over 1-2 weeks.
Monitoring for the first 12 months
Track 3 numbers at home: urine clump size in the litter box, body weight every 2 weeks, and how long the cat stays in the box. A clump under 2 cm, a 5% weight drop, or 5 minutes of straining are the 3 triggers to call. Recheck at 2 weeks, 6 weeks, 6 months, and 12 months, because most re-narrowing shows up in the first 6 months. A cat that has had 1 stricture stays on that schedule for life if the cause was a scar.
Prevention is mostly about catheters: ask whether a catheter is truly needed, ask for the smallest size that works, and ask for it out within 24-48 hours. For stone-prone cats, keep the water intake up with wet food and 3-4 water points around the house, and recheck urine at 4 weeks after any episode.
Terms mentioned in this article
Frequently asked
How do I tell a stricture from a normal blockage at home?
You cannot, and the distinction does not change the first hour of care. A thin stream, repeated small clumps, and 5 minutes of straining all mean the same thing tonight: a vet visit with a bladder check. Only imaging after stabilisation separates the 3 causes.
Can a stricture open up on its own?
Inflammatory narrowing around a stone can ease once the stone passes or dissolves, which is why a recheck at 4 weeks matters. Scar tissue does not stretch back by itself; it needs balloon dilation, an incision, a stent, or reconstruction to widen the lumen again.
Is a stent a permanent fix?
It is permanent in the sense that it stays in place and keeps a 6 to 8 mm channel open. It is not a cure for the underlying cause, and it raises urinary infection risk, so urine checks every 3 to 4 months for the rest of the cat's life are part of the deal.