What Is Hydroureter? Causes, Symptoms, and Treatment

Hydroureter is the abnormal widening, or dilation, of one or both ureters, the narrow muscular tubes that carry urine from each kidney down to the bladder. In a healthy urinary tract, each ureter is only a few millimeters wide and moves urine along through rhythmic muscular contractions. When something blocks that flow or the ureter’s muscle wall stops working properly, urine backs up and the tube balloons outward. The condition can range from a minor finding on an imaging scan to a serious problem that threatens kidney function, depending on the cause and how long the dilation has been present.

How the Ureter Normally Moves Urine

Your ureters are not passive drainpipes. They push urine toward the bladder through coordinated waves of muscle contraction called peristalsis, similar in concept to the way your intestines move food. A natural pacemaker system in the upper part of the kidney’s collecting area sets the rhythm, and each wave of squeezing travels down the full length of the ureter. When that coordination breaks down, urine can flow backward between contractions, pool inside the ureter, and stretch the walls outward. Research modeling ureteral dynamics has shown that when the tube’s lengthwise motion is absent or the squeezing force is too weak, retrograde flow and urine pooling result, setting the stage for both dilation and a higher risk of urinary infection. Chronically high bladder pressures make this even worse by making the ureter more susceptible to backward flow during each contraction cycle.¹

Once a blockage has been in place for a while, it can damage the pacemaker system itself. Studies on chronically obstructed ureters have found that the contraction rhythm in the upper kidney area falls out of sync with the ureter below, meaning even after the original blockage is cleared, the tube may not return to normal peristalsis right away.² This helps explain why some patients still show a dilated ureter on imaging even after the obstruction has been treated.

Common Causes

Doctors generally sort the causes of hydroureter into a few broad categories based on where and how the blockage or malfunction occurs.

Obstruction From Inside the Ureter

The most straightforward cause is something physically blocking the tube from within. Kidney stones that migrate down into the ureter are the classic example; a stone lodged partway down creates a dam behind which urine accumulates, and the ureter dilates above the obstruction. Ureteral strictures, which are areas of scar tissue that narrow the channel, can develop after surgery, radiation therapy, infection, or chronic inflammation. Tumors growing within the ureter wall are a less common but more concerning possibility.

Compression From Outside the Ureter

Anything pressing on the ureter from the surrounding tissues can pinch it shut. Pelvic tumors, enlarged lymph nodes, and inflammatory conditions can all do this. In women, endometriosis is a well-recognized extrinsic cause. Endometrial-like tissue can implant on the peritoneal lining near the ureter, triggering inflammation and lateral spread of lesions that eventually wrap around and compress it.³ Retroperitoneal fibrosis, a rare condition where scar-like tissue develops behind the abdominal organs, is another cause that can trap one or both ureters.

Surgical Injury

The ureters run close to many structures that surgeons routinely operate on, which makes accidental damage a recognized risk. Gynecologic, colorectal, and vascular pelvic surgeries are the most frequent settings for iatrogenic ureteral injury.⁴ A clipped, kinked, or partially cut ureter can swell upstream. Endoscopic procedures done inside the ureter itself, such as stone removal or tumor biopsy, carry their own small risk of injury and subsequent stricture.

Reflux and Functional Problems

Not every dilated ureter has a physical blockage. In vesicoureteral reflux, the valve-like mechanism where the ureter meets the bladder fails, and urine washes backward up into the ureter during bladder contraction. Over time, the repeated pressure waves stretch the tube. This is one of the most common causes of hydroureter in children. In some cases, no reflux and no obstruction can be identified at all, and the dilated ureter is labeled “non-reflux non-obstructive,” essentially a diagnosis of exclusion.⁵

Hydroureter in Pregnancy

If you are pregnant and an ultrasound mentions a dilated ureter, the most likely explanation is entirely normal. As the uterus grows, it compresses the ureters where they cross the pelvic brim. Hormonal changes also relax the smooth muscle of the ureter wall, reducing its ability to push urine through efficiently. The result is some degree of ureteral and kidney-pelvis dilation in the majority of pregnancies, with estimates suggesting it appears in up to about 80% of pregnant women.⁶ The right side is almost always more affected than the left, because the uterus naturally tilts slightly rightward and the left ureter gets some protection from the sigmoid colon. This pregnancy-related hydroureter resolves on its own after delivery and usually requires no treatment, though it does increase the risk of urinary tract infections during pregnancy.

Congenital Hydroureter in Children

Hydroureter detected before birth or in infancy often traces back to how the urinary tract formed during fetal development. A range of structural abnormalities can be responsible. If the ureteric bud, the embryonic structure that gives rise to the ureter, forms in the wrong spot or fails to mature properly at its junction with the bladder, the child can be born with vesicoureteral reflux, an ectopic ureter that opens in the wrong location, or a ureterocele, which is a balloon-like swelling at the end of the ureter inside the bladder.⁷ All of these can lead to hydroureter. A primary obstructive megaureter, where the lowest segment of the ureter is too narrow or doesn’t contract properly, is another common congenital finding.

Many of these conditions are first spotted on prenatal ultrasound, and the parents’ natural instinct is to worry about surgery. In practice, though, a large proportion of congenital megaureters improve on their own. A longitudinal study following infants with primary non-refluxing megaureter found that all cases with mild dilation resolved or improved, and close to 60% of those with moderate or severe dilation did too. Surgery was rarely needed during the first year of life.⁸ Observation with periodic imaging is the standard first approach for stable infants.

Symptoms and When to Worry

Hydroureter itself does not always produce symptoms, and many cases are found incidentally on imaging done for another reason. When symptoms do appear, they tend to come from whatever is causing the dilation rather than from the stretched ureter alone. The most common complaints include flank or lower abdominal pain, especially if a stone or acute obstruction is involved, and urinary tract infections. Chronic or low-grade obstruction can be surprisingly silent and discovered only when kidney function tests come back abnormal.

Pain that comes with hydroureter often has a colicky quality, meaning it comes in waves, because the ureter keeps trying to squeeze urine past the blockage. If infection accompanies the obstruction, you might develop fever, chills, and cloudy or foul-smelling urine. This combination of obstruction plus infection, called obstructive uropathy with urosepsis, is a urological emergency. The infected urine has nowhere to drain, and bacteria can enter the bloodstream quickly. Anyone with severe flank pain and a high fever should be evaluated immediately.

Less obvious presentations do occur. Duplicated ureteral systems, a relatively common anatomical variant, can cause chronic pelvic pain and recurrent urinary infections that go undiagnosed for years before the underlying structural abnormality is identified.

How Hydroureter Is Diagnosed

Ultrasound is the usual first step because it is fast, widely available, and involves no radiation. It can show whether the ureter and kidney pelvis are dilated and sometimes identifies the cause, such as a visible stone or mass. A CT scan with or without contrast offers much more anatomical detail and is the go-to test when the ultrasound is inconclusive or when a stone, tumor, or retroperitoneal process is suspected. For children and pregnant women, where minimizing radiation matters, ultrasound combined with MRI often provides enough information.

Functional studies add another layer. A diuretic renogram, which uses a small amount of radioactive tracer to watch how each kidney handles a fluid challenge, helps determine whether a dilated system is truly obstructed or just floppy but draining adequately. This distinction matters because a wide ureter that drains well may not need any intervention. When reflux is suspected, a voiding cystourethrogram, which involves filling the bladder with contrast and watching whether it flows backward during urination, is the standard test.

Emergency Drainage

When the kidney behind an obstructed, dilated ureter is in danger, whether from infection, rising pressure, or declining function, the priority is relieving the obstruction as quickly as possible. Two main approaches exist. A retrograde ureteral stent is placed by threading a thin tube up from the bladder into the ureter during a cystoscopy. A percutaneous nephrostomy involves placing a drainage tube directly through the skin of the back into the swollen kidney, guided by ultrasound or X-ray.

Both methods work for decompression, and a systematic review and meta-analysis found no significant difference in most outcomes between the two.⁹ However, there are situations where one is preferred over the other. In patients with urosepsis, a study comparing the two approaches found that percutaneous nephrostomy produced a faster drop in inflammatory markers and quicker fever resolution.¹⁰ On the other hand, nephrostomy tubes require an external drainage bag and slightly longer hospital stays, while internal stents are invisible from the outside but can cause more bladder irritation.

Surgical Options for Definitive Repair

Once the acute crisis is managed, or when the underlying cause clearly will not resolve on its own, definitive surgery addresses the root problem. The specific procedure depends on what is causing the hydroureter and where along the ureter the issue sits.

Ureteral reimplantation is among the most common reconstructive operations for hydroureter caused by vesicoureteral reflux or obstruction at the ureterovesical junction. The surgeon detaches the ureter from its current entry point into the bladder and reattaches it in a way that creates a functioning one-way valve, preventing reflux. In adults, when a section of ureter has been lost to injury or disease, a psoas hitch reimplantation is a well-established technique. The bladder is mobilized upward and sutured to the psoas muscle of the pelvis, shortening the gap the ureter needs to bridge and allowing a tension-free connection without needing to use intestinal tissue.¹¹

In children with primary obstructive megaureter or high-grade reflux, reimplantation has increasingly moved toward minimally invasive approaches. Laparoscopic and robot-assisted techniques are gaining traction, with reports describing effective outcomes in children as young as 15 months.¹² When the dilated ureter is excessively wide, the surgeon may taper or plicate it, folding the excess tissue and suturing it to bring the diameter closer to normal before reimplanting it.¹³

For less severe cases or when surgery poses too high a risk, endoscopic options like balloon dilation of a narrowed segment or temporary stent placement may be enough.¹⁴ These approaches avoid a full surgical reconstruction, though they sometimes serve as a bridge rather than a permanent fix.

Conservative Management and Watchful Waiting

Not every dilated ureter needs an operation. In many pediatric cases, especially when the megaureter is detected prenatally and the child is otherwise healthy, watchful waiting with regular imaging is the accepted strategy. A study tracking infants with primary megaureter over an average of about six years found that the average diameter of the dilated ureter shrank from roughly 14 mm in the newborn period to around 8 mm by the end of follow-up, with kidney function remaining stable throughout.¹⁵

Whether to prescribe preventive antibiotics during observation is a judgment call. In infants with mild dilation, the rate of urinary infections is low enough that prophylactic antibiotics may not be necessary. In those with moderate or severe dilation, infections can still occur despite prophylaxis, and children who do develop symptomatic infections often end up hospitalized.⁸ Observation as a management strategy for congenital non-refluxing hydronephrosis, megaureter, and ureterocele is supported as a reasonable first-line option in the absence of complications.¹⁶

For adults, conservative management plays a different role. If the cause is pregnancy, the dilation resolves after delivery. If a mild stricture or small stone is involved, observation with pain management and hydration may be appropriate while waiting to see whether the obstruction clears on its own. Stones under a certain size have a reasonable chance of passing spontaneously, and the hydroureter resolves once they do.

Can the Kidney Recover After Prolonged Dilation?

One of the most common worries for patients with hydroureter is whether their kidney has already suffered permanent damage. The answer depends mostly on how long the obstruction lasted and how severe it was. A kidney that has been partially obstructed for weeks to a few months often regains most or all of its function once the blockage is relieved. Complete obstruction left untreated for months can cause irreversible damage, though even some severely compromised kidneys may recover more function than older medical teaching would have predicted.

This is why timing matters. Prompt drainage of an obstructed system, even when the obstruction cannot be definitively fixed right away, preserves kidney tissue while a longer-term plan is worked out. Follow-up functional imaging after treatment helps determine whether the kidney is recovering or whether the damage has already become permanent, which in turn guides decisions about further surgery.

Living with a Ureteral Stent

Many patients with hydroureter will have a ureteral stent placed at some point during their treatment, whether temporarily to relieve an acute obstruction or as part of a surgical recovery. Stents are effective at keeping the ureter open, but they come with real quality-of-life costs that are worth knowing about in advance.

A study tracking stent-related symptoms over time found that roughly 78% of patients reported bothersome urinary symptoms including frequent urination, urgency, incontinence, and blood in the urine. Over 80% experienced pain that affected daily activities, about a third reported sexual dysfunction, and close to 60% said the stent reduced their ability to work.¹⁷ Symptoms tend to be worst in the first week after placement, with frequency, burning, urgency, and visible blood in the urine all peaking during that window. Quality-of-life scores improved after stent removal, returning closer to baseline within about two weeks.¹⁸

If you are about to have a stent placed, knowing this in advance helps set realistic expectations. Most of the discomfort is temporary, and medications for bladder spasm and pain can ease the worst of it. Staying well hydrated helps reduce irritation, and avoiding heavy physical activity in the first few days can limit blood in the urine. The stent is a means to an end: it protects the kidney while the underlying problem is being resolved, and the symptoms stop once it comes out.