A ureterocele is a balloon-like swelling at the end of a ureter, the tube that carries urine from the kidney to the bladder. Instead of the ureter opening normally into the bladder, its tip puffs outward into a fluid-filled pouch that can block urine flow. The condition affects roughly 1 in 5,000 to 1 in 12,000 children and is more common in females. While some ureteroceles are small and cause no trouble, others lead to recurring infections, kidney swelling, and urinary problems that require surgery.
How a Ureterocele Forms
During early fetal development, a thin membrane temporarily separates the forming ureter from the developing bladder. This membrane normally dissolves around the fifth week of pregnancy, creating an open passage for urine. When it fails to dissolve completely, the end of the ureter stays partially sealed. Urine pressure pushes against this sealed tissue, inflating it into a cyst-like bulge inside (or sometimes beyond) the bladder wall.
That membrane theory is the most widely accepted explanation, but it doesn’t account for every case. Some ureteroceles appear to result from abnormal muscle development in the lower ureter: without proper muscular support, the tissue balloons outward. A third possibility is that the same growth signals driving bladder expansion simultaneously overexpand the portion of the ureter embedded in the bladder wall. In reality, multiple genetic and developmental factors likely interact to produce the defect.
Types of Ureteroceles
Ureteroceles fall into two broad categories based on location. An intravesical (orthotopic) ureterocele sits entirely inside the bladder. It may bulge toward the bladder neck, but its walls originate within the bladder itself. An ectopic (extravesical) ureterocele extends beyond the bladder, with tissue reaching into or past the bladder neck and into the urethra.
The condition also relates to how the kidney’s drainage system is organized. In a single collecting system, one ureter drains the whole kidney. In a duplex system, two ureters drain different parts of the same kidney. Ureteroceles associated with duplex systems are more common in children and tend to be more complex, because the abnormal ureter typically drains the upper portion of the kidney while a second, normal ureter drains the lower portion. This distinction matters for treatment planning, since duplex-system ureteroceles more often require follow-up surgery.
Symptoms to Recognize
Many ureteroceles are discovered before birth on routine prenatal ultrasound, appearing as a round, fluid-filled structure in or near the bladder. When they aren’t caught early, symptoms usually show up as urinary tract infections, particularly in infants and young children. Fever, foul-smelling urine, irritability, and poor feeding can all signal a UTI driven by trapped urine behind the ureterocele.
Larger ureteroceles can physically block the bladder outlet. In children and adults alike, this causes difficulty urinating, a weak stream, or in severe cases, complete urinary retention. Chronic blockage backs urine up into the kidney, a condition called hydronephrosis. In thin adults or young children, a swollen kidney may be felt as a mass in the upper abdomen. Infants with significant hydronephrosis sometimes have a visible or palpable abdominal bulge.
In rare cases (fewer than 5% of symptomatic ureteroceles), a girl or woman may notice a grape-like bulge protruding from the urethral opening. This is a prolapsing ureterocele, where the cyst pushes through the urethra and becomes visible externally.
Possible Complications
The core problem with a ureterocele is obstructed urine flow. Stagnant urine breeds bacteria, leading to repeated UTIs. Left untreated, infections can progress to kidney infections or, in serious cases, bloodstream infection. Chronic back-pressure on the kidney can cause permanent scarring and, over time, reduced kidney function on the affected side.
Ureteroceles can also cause vesicoureteral reflux, where urine flows backward from the bladder toward the kidneys. Reflux further raises the risk of kidney infections, incontinence, and bedwetting. Stones can form inside the ureterocele itself when urine sits stagnant for long periods.
How It’s Diagnosed
Ultrasound is typically the first test. It can show the cystic bulge at the base of the ureter, any swelling of the ureter or kidney above it, and whether the kidney has a single or duplex collecting system. Prenatal ultrasounds catch many cases before a child is born.
A voiding study, where contrast dye is placed into the bladder through a catheter and X-rays are taken while the child urinates, checks for backward flow of urine into the kidneys. On older-style contrast X-rays, ureteroceles produce a characteristic “cobra head sign,” a round, halo-like shadow at the base of the ureter that looks like a cobra with its hood spread. A nuclear kidney scan may be ordered to measure how well each portion of the kidney is working, which helps guide surgical decisions.
Treatment Options
Small, incidentally discovered ureteroceles that cause no symptoms or kidney swelling can sometimes be monitored with periodic ultrasounds. When treatment is needed, the triggers are usually recurring UTIs, worsening kidney function, stone formation, or significant pain.
Endoscopic Incision
The least invasive approach involves passing a small scope through the urethra and making a puncture or cut in the ureterocele wall to release trapped urine. No external incision is needed. This is often the first step for newborns with infection or significant obstruction because it provides immediate relief. For single-system intravesical ureteroceles, endoscopic incision resolves the problem permanently in 80 to 90% of cases. Results are less definitive for ectopic ureteroceles, where only 10 to 40% are fully treated by the initial incision alone.
Long-term data show that about 41% of children who undergo endoscopic incision eventually need a second, more involved operation. The likelihood of reoperation is significantly higher for ectopic ureteroceles (64%) than intravesical ones (18%), and children with a duplex collecting system are also more likely to need additional surgery (52%) compared to those with a single system (15%). Preoperative reflux is another factor: roughly 64% of children who had reflux before the incision needed a second procedure, versus about 26% of those without reflux.
Bladder Reconstruction
When the ureterocele causes significant reflux or the initial endoscopic approach doesn’t solve the problem, open or robotic surgery to remove the ureterocele and reimplant the ureter into the bladder in a new position is the next step. This creates a proper anti-reflux connection. If both ureters in a duplex system need correction, both are reimplanted during the same procedure.
Partial Kidney Removal
In duplex systems where the upper portion of the kidney has been badly damaged by chronic obstruction and contributes little to no function, removing that upper segment along with its associated ureter is a reasonable first-line option, provided there’s no significant reflux. The healthy lower portion of the kidney continues to function normally. If reflux is present, the surgeon ties off the remaining distal ureter during the same operation to prevent backflow.
Internal Reconnection
When the affected portion of the kidney still works well and there’s no reflux, a surgeon can connect the upper-pole ureter directly to the lower-pole drainage system, bypassing the ureterocele entirely. This preserves kidney tissue and avoids the need for bladder surgery.
What Recovery Looks Like
After an endoscopic incision, most children go home the same day or the following morning. A short course of antibiotics is standard to prevent infection. Follow-up ultrasounds track whether kidney swelling improves and whether the ureterocele stays decompressed. For open reconstructive surgery, hospital stays are typically a few days, with a catheter in place while the bladder heals. Full recovery from open procedures generally takes several weeks, though most children return to normal activity well before that.
Because the rate of needing a second procedure is significant, especially for ectopic and duplex-system ureteroceles, ongoing monitoring with periodic imaging is a routine part of care. The goal at each stage is preserving as much kidney function as possible while eliminating the cycle of obstruction and infection.