What Is a Ureteral Stricture and What Causes It?

A ureteral stricture is a narrowing of the ureter, one of the two thin tubes that carry urine from your kidneys down to your bladder, that blocks or slows the flow of urine enough to cause problems upstream. Left alone, that obstruction can back urine up into the kidney and eventually damage it.¹ The causes range from surgical accidents and kidney stones to infections and radiation treatment, and occasionally the narrowing is something a person is born with. Understanding why a stricture forms matters because the cause shapes which part of the ureter is affected, how severe the blockage becomes, and what kind of repair is most likely to work.

How the Ureter Normally Works

Each ureter is a muscular tube roughly 25 to 30 centimeters long that connects a kidney to the bladder. It does not rely on gravity alone. Layers of muscle fibers in the ureteral wall contract in coordinated waves, a process called peristalsis, that actively squeezes urine downward. Those contractions are triggered by natural pacemaker cells near the kidney and travel along the ureter like a ripple, pushing each small bolus of urine toward the bladder.² The inner lining of the ureter, called the urothelium, is stretchy enough to accommodate variable urine flow, while the outer muscular layers provide the force.

A stricture disrupts that system at a specific point. When the tube narrows, the peristaltic wave hits a bottleneck. Urine accumulates above the narrowing, the upstream ureter dilates, and eventually the kidney itself swells with backed-up urine, a condition called hydronephrosis. The kidney can tolerate mild swelling for a while, but prolonged obstruction gradually destroys kidney tissue.

What Happens Inside the Ureteral Wall During a Stricture

Regardless of the original trigger, most ureteral strictures share a common endpoint: fibrosis. The body responds to ureteral injury or chronic irritation by laying down scar tissue. Fibroblasts, the cells that produce collagen and other structural proteins, multiply in the damaged area. Over time, collagen accumulates and the tissue loses its normal elasticity. Research examining stricture tissue has identified distinct patterns of scarring. In some specimens, fibroblast activity dominates; in others, the collagen itself undergoes a process called hyalinization, becoming dense and glass-like. Hyalinized strictures tend to contain the most type I and type III collagen of any pattern.³

The practical consequence is that a mature stricture is not just a temporary swelling you can wait out. Once the wall has been replaced by stiff scar tissue, the ureter cannot contract through that segment. The narrowing becomes structural, and treatment usually requires physically opening or bypassing the scarred area rather than simply reducing inflammation.

Surgical and Procedural Causes

The single most common reason someone develops a ureteral stricture is an injury that happens during surgery. Doctors sometimes refer to these as iatrogenic injuries, meaning they are an unintended consequence of medical care. The ureters sit close to organs that surgeons frequently operate on, particularly in the pelvis, and their thin walls are vulnerable to being nicked, clamped, cauterized, or kinked.

Gynecological procedures account for the largest share. Hysterectomies, cesarean sections, and operations for conditions like ovarian cysts or pelvic tumors all involve working near the ureters. Estimates suggest that somewhere between half and four-fifths of all iatrogenic ureteral injuries happen during gynecological surgery, with the overall rate of ureteral trauma from those procedures falling between about 0.5% and 1.5%.⁴ Colorectal and vascular abdominal surgeries also carry risk, though they account for a smaller fraction of cases.⁴ The injury may not be recognized during the operation itself. Sometimes the damage only becomes apparent weeks or months later, once scar tissue has formed around the injured site and a stricture has developed.

Strictures After Stone Procedures

Ureteroscopy, the procedure where a thin scope is passed up through the ureter to break up or retrieve kidney stones, is extremely common and generally safe. But the scope and the laser or mechanical tools used to fragment the stone can irritate or injure the ureteral lining, especially in difficult cases. A large systematic review found a pooled stricture rate of about 1.9% after ureteroscopy. That number has crept up in more recent studies to around 2.7%, likely because more complex cases are being treated endoscopically now rather than with open surgery.⁵

Certain factors push the risk considerably higher. If the stone is impacted, meaning it has been stuck in one spot long enough to embed in the ureteral wall, the stricture rate climbs to roughly 5%. Tearing through the ureteral wall during the procedure (a perforation) raises the odds by about sevenfold. Having hydronephrosis before the procedure or having the stone lodged in the upper part of the ureter also increases risk.⁵

Kidney Stones Themselves as a Cause

You do not necessarily need a procedure to get a stricture from a stone. A stone that sits in the ureter for weeks or months does its own damage. The constant pressure of the stone against the ureteral wall causes localized ischemia, which is a loss of blood flow to the tissue pressing against it. That triggers chronic inflammation, the urothelial lining thickens, and interstitial fibrosis sets in around the site of impaction.⁶ Some researchers also suspect an immune reaction to the stone material itself contributes to the scarring.

Studies using endoscopic examination of patients with long-standing impacted stones have shown that about 17% already had a visible stricture at the time the stone was finally dealt with. The patients who developed strictures had stones that had been stuck for a median of 24 months, far longer than patients whose ureters remained normal. Inflammatory polyps, small fleshy growths on the ureteral lining, appeared in about 31% of patients and were associated with a median impaction time of 12 months.⁷ The takeaway is straightforward: the longer a stone sits in the ureter, the more structural damage it causes, and the greater the chance a stricture will form even if the stone is eventually cleared.

Radiation-Induced Strictures

Radiation therapy aimed at cancers in the pelvis, including cervical, rectal, bladder, and prostate cancers, can injure the ureters as bystanders. The mechanism involves radiation damaging the small blood vessels that supply the ureteral wall. That ischemia leads to progressive fibrosis and contraction, which gradually narrows the lumen over months to years after treatment ends.⁸

Radiation strictures are particularly frustrating to manage because the damage is not limited to a discrete spot. The affected tissue tends to be poorly vascularized over a long stretch, which means it heals badly and is prone to re-narrowing after repair. Surgeons often need to bring in healthy tissue from other parts of the body, such as a segment of bowel or a tissue graft, to bridge the gap where the irradiated ureter cannot be salvaged. The delayed onset also means that a patient who finishes cancer treatment and feels well can develop a new urinary problem a year or more down the line.

Infections That Scar the Ureter

Ordinary urinary tract infections do not usually cause ureteral strictures, but certain chronic or granulomatous infections can. Tuberculosis is the classic example. Genitourinary tuberculosis can present in unusual ways, sometimes affecting an isolated segment of the ureter without obvious signs of TB elsewhere. In one reported case, a patient with persistent flank pain was found to have a short stricture in the lower ureter. Biopsies during ureteroscopy revealed granulomatous inflammation with caseous necrosis, the hallmark of TB, confirming the diagnosis.⁹ In parts of the world where TB remains common, it should be on the radar when a stricture is found without an obvious surgical or stone-related history.

Schistosomiasis, a parasitic infection spread by freshwater snails in parts of Africa and the Middle East, is another well-known culprit. The parasites deposit eggs in the walls of the urinary tract, provoking a chronic inflammatory response that leads to calcification and scarring. Severe cases can produce long-segment strictures requiring major reconstructive surgery, such as replacing a section of the ureter with a piece of small intestine.¹⁰

Endometriosis and Other Extrinsic Compression

Not all strictures originate inside the ureter. Sometimes the narrowing is caused by something pressing on the ureter from outside. Endometriosis, a condition in which tissue similar to the uterine lining grows in abnormal locations, is one of the more common causes of extrinsic ureteral compression in premenopausal women. Endometriotic deposits can grow on or around the ureter, squeezing it shut without ever penetrating the wall. In a study of 30 patients with ureteral endometriosis, about 87% had the extrinsic pattern, where the disease compressed the ureter from the outside, while only about 13% had intrinsic involvement where the tissue had actually grown into the ureteral wall.¹¹

What makes ureteral endometriosis tricky is that it is often silent. In the same study, two-thirds of patients had no urinary symptoms at all. When symptoms did appear, they included painful urination and flank pain, but a third of patients already had hydronephrosis by the time the condition was discovered. The left ureter is affected more often than the right, possibly because of its proximity to the sigmoid colon and the rectouterine pouch where endometriosis frequently implants.

Other conditions that can compress the ureter from outside include retroperitoneal fibrosis, a rare disorder where inflammatory scar tissue encases the ureters and large blood vessels behind the abdominal cavity, as well as cancers or enlarged lymph nodes in the pelvis and abdomen. These extrinsic causes need to be distinguished from intrinsic ones because treatment often involves addressing the underlying disease rather than operating on the ureter itself.¹²

Congenital Narrowing

Some people are born with a narrowing at the junction where the ureter meets the kidney, called ureteropelvic junction (UPJ) obstruction. This is actually the most frequently identified cause of hydronephrosis in newborns and infants, occurring in roughly 1 in every 1,000 to 1,500 births. The narrowing is usually functional rather than a physical blockage: the smooth muscle cells in the ureteral wall at that junction did not develop normally, so peristaltic waves cannot travel through the area effectively.¹³

In some cases, a blood vessel crossing over the ureter at the junction contributes to the obstruction by physically kinking it, though whether the vessel alone is sufficient to cause problems or whether there is always an underlying muscular abnormality remains debated. Tissue taken from patients who have undergone surgical repair consistently shows abnormal smooth muscle arrangement and disrupted nerve signaling in the affected area.¹³ Many mild cases detected on prenatal ultrasound resolve on their own as the child grows, but significant obstruction requires surgery to widen or reconstruct the junction.

Trauma From Outside the Body

Ureteral injuries from external trauma, whether from car accidents, falls, or penetrating wounds, are uncommon. The ureters account for less than 1% of all urologic injuries from external causes. Penetrating injuries such as stab or gunshot wounds are more likely to damage the ureter than blunt force, and the upper third of the ureter is injured more often than the lower portions.¹⁴

The danger with traumatic ureteral injury is that it is easy to miss. The ureter is deep in the body, it doesn’t bleed dramatically the way a lacerated kidney or liver might, and the patient usually has other more immediately life-threatening injuries that dominate attention. A missed ureteral injury can quietly progress to a stricture as the torn tissue heals with scar formation, ultimately presenting weeks later with flank pain, infection, or deteriorating kidney function on that side.

How Strictures Are Found

Ureteral strictures rarely announce themselves with a single unmistakable symptom. Flank pain, recurrent urinary infections, reduced urine output, or unexplained kidney swelling on imaging often trigger the workup. The first step is usually a CT urogram, a specialized CT scan where contrast dye is given intravenously so it is excreted by the kidneys and outlines the entire urinary tract. This can reveal the site of the narrowing and whether the kidney above it is dilated.

When a CT urogram does not fully visualize a segment of the ureter, or when more detail is needed, doctors may perform a retrograde pyelogram. This involves threading a small catheter up through the bladder and into the ureter, then injecting contrast dye directly to map the blockage. In one study evaluating ureters that were incompletely visualized on CT, retrograde pyelography picked up strictures and other abnormalities that the CT had missed.¹⁵ The combination of these imaging approaches helps surgeons pinpoint not just where the stricture is, but how long it is, which directly influences what kind of repair is feasible.

In transplant recipients, where the ureter connecting a donor kidney to the bladder follows an unusual surgical path, specialized retrograde CT urography has proven useful for localizing complications with high spatial resolution and guiding timely decisions about repair.¹⁶

Why the Cause Matters for Treatment

The way a stricture formed has a direct bearing on how it is repaired, because different causes produce different patterns of damage. A short stricture from a brief surgical injury, where the surrounding tissue is healthy, may be amenable to a relatively simple approach: the surgeon incises the scar lengthwise and patches it with a graft of tissue, often harvested from the inside of the cheek (buccal mucosa) or the tongue (lingual mucosa). That graft is then wrapped in omentum, the fatty apron that hangs inside the abdomen, to give it a blood supply and help it heal.¹⁷

By contrast, a long stricture from radiation or chronic schistosomiasis may have destroyed so much of the ureter that a patch is not enough. In those cases, surgeons sometimes replace an entire section of the ureter with a tube fashioned from a segment of small intestine or use the bladder itself to bridge the gap. The surrounding tissue quality matters enormously: irradiated tissue heals poorly, so grafts placed into a radiation field are at higher risk of failing. Strictures caused by extrinsic compression from endometriosis or retroperitoneal fibrosis may not require ureteral surgery at all if the underlying disease can be controlled with hormonal therapy or immunosuppressive medication.

Experimental Approaches to Preventing Scar Formation

Because fibrosis is the final common pathway for virtually all ureteral strictures, researchers have begun exploring whether the scarring process itself can be interrupted. One line of investigation involves using stem cells derived from bone marrow. In animal studies, injecting mesenchymal stem cells into injured ureters reduced the amount of scar tissue that formed. The cells appear to work not by replacing the damaged tissue directly, but by releasing tiny packets of signaling molecules called extracellular vesicles that calm the inflammatory response and discourage fibroblasts from overproducing collagen.¹⁸

This is still laboratory-stage work, not something available in clinics. But it reflects a broader shift in thinking about strictures: rather than waiting for a scar to form and then cutting it out, the goal is to intervene during the healing process to prevent the scar from becoming a problem in the first place. Anti-fibrotic drugs, drug-coated stents, and bioengineered ureteral grafts are all being investigated, though none has yet moved into routine clinical use. For now, the practical message for patients remains early recognition and timely repair, because the longer a stricture goes unaddressed, the more kidney function is lost and the harder the reconstruction becomes.

1
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PubMed Central. A computational model of ureteral peristalsis and an investigation into ureteral reflux
3
PubMed Central. Main Pathological Changes of Benign Ureteral Strictures
4
PubMed Central. Iatrogenic ureteral injury after gynecological surgery
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The Journal of Urology. Ureteral Stricture Formation After Removal of Impacted Calculi
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PubMed. Endoscopic features of impacted ureteral stones
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PubMed Central. Management of Ureteral Stricture Disease After Radiation Therapy for Pelvic Malignancies: A Retrospective, Multi-Institutional Analysis
9
Scholars Journal of Medical Case Reports. Isolated Distal Ureteral Tuberculosis Presenting as Renal Colic: A Case Report and Literature Review
10
PubMed Central. Complex ureteral stricture from chronic schistosomiasis requiring ileal ureter interposition: a case report
11
PubMed. Importance of retroperitoneal ureteric evaluation in cases of deep infiltrating endometriosis
12
Human Reproduction Update. Ureteral endometriosis: a systematic review of epidemiology, pathogenesis, diagnosis, treatment, risk of malignant transformation and fertility
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PubMed Central. Congenital ureteropelvic junction obstruction: human disease and animal models
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PubMed Central. A review of ureteral injuries after external trauma
15
PubMed. The utility of retrograde pyelography to follow up incompletely opacified ureters on CT urography
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PubMed Central. Optimizing the Diagnosis of Ureteral Complications After Kidney Transplantation Using Retrograde Multidetector Computed Tomography Urography: A Case Series
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Urologia Internationalis. Ureteroplasty for the Repair of Ureteral Stricture Using Lingual Mucosa and Buccal Mucosa Grafts: A Meta-Analysis
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PubMed Central. Bone marrow mesenchymal stem cells reduce ureteral stricture formation in a rat model via the paracrine effect of extracellular vesicles