A urinoma is an enclosed collection of urine that has leaked out of the urinary tract and pooled in the surrounding tissue. Instead of flowing from the kidneys through the ureters to the bladder and out of the body, urine escapes through a tear or defect somewhere along that path and becomes trapped, usually in the space behind the abdominal organs. Over time, this leaked urine can become walled off by the body’s tissues, forming a distinct fluid-filled pocket that grows as more urine accumulates.
How a Urinoma Forms
Urine is normally contained within a sealed system: the kidneys, ureters, bladder, and urethra. When any part of that system is damaged or blocked, urine can escape into surrounding tissue. The leak might come from a cracked kidney, a torn ureter, or a hole in the bladder wall. Once urine is outside the urinary tract, the body treats it as a foreign substance. Surrounding tissue reacts to the irritation by forming a fibrous capsule around the fluid, creating a defined collection rather than letting urine spread freely.
The collection typically sits in the retroperitoneal space, the area behind the lining of the abdominal cavity where the kidneys and ureters are located. In some cases, urine can leak into the abdominal cavity itself, especially if the bladder is the source. A urinoma can range from a small pocket a few centimeters across to a large mass that causes visible swelling and compresses nearby organs.
Common Causes
Trauma is one of the most frequent triggers. Blunt force injuries from car accidents or falls can fracture a kidney or tear a ureter, allowing urine to leak into the surrounding tissue. Penetrating injuries like stab wounds can do the same. In younger adults, motor vehicle accidents are a particularly common scenario.
Surgery is another major cause. Any operation near the urinary tract carries some risk of accidental injury to the ureters or bladder. Procedures for rectal cancer, pelvic surgery, and gynecological operations can all lead to urine leaks. Kidney transplant is a well-documented risk factor, with urine leaks occurring in roughly 2% to 6% of transplant recipients. Kidney stone procedures, including lithotripsy, can also cause small tears in the urinary collecting system.
Obstruction plays a role as well. When a kidney stone, tumor, or other blockage prevents urine from draining normally, pressure builds in the system until the weakest point gives way. This can happen spontaneously in some cases. In pregnant women, the growing uterus can compress a ureter enough to cause a rupture. In fetuses, severe urinary tract obstruction (such as a blockage at the junction where the kidney meets the ureter) can cause a urinoma to form before birth. Self-catheterization, while generally safe, can occasionally perforate the urethra and lead to urine collecting in nearby soft tissue.
Symptoms to Recognize
Urinomas don’t always announce themselves clearly, which is part of what makes them tricky to catch. Some are clinically silent at first, producing no obvious symptoms until they grow large enough to cause problems. When symptoms do appear, they tend to be nonspecific: abdominal or flank pain, a general feeling of being unwell, fever, nausea, or vomiting. You might notice a palpable mass or swelling in your abdomen or lower back that gradually gets larger.
The overlap with other conditions is significant. Abdominal tenderness and signs of peritoneal irritation can mimic appendicitis, a ruptured ovarian cyst, diverticulitis, or gallbladder disease. A decrease in urine output is another clue, since urine that leaks into a urinoma never reaches the bladder. In newborns, a large urinoma can cause abdominal distension and even respiratory distress by pushing up on the diaphragm. An inability to urinate at all is a red flag that warrants emergency care.
How It’s Diagnosed
A CT scan with contrast is the primary diagnostic tool. The key technique involves delayed imaging, where the scan is repeated several minutes after contrast dye is injected. By that point, the dye has been filtered by the kidneys and entered the urine. If urine is leaking, the delayed images will show contrast material accumulating inside the fluid collection, confirming that it’s a urinoma rather than blood, an abscess, or another type of fluid. On early scans, the collection may look like ordinary fluid, but the delayed phase reveals the telltale bright signal of contrast-enhanced urine mixing into the pocket.
Ultrasound can also identify a fluid collection near the kidney or in the pelvis, though it’s less specific about what the fluid actually is. CT cystography (where contrast is instilled directly into the bladder) helps when a bladder leak is suspected, and retrograde urethrography is useful for urethral injuries.
When fluid is drained from a suspected urinoma, a simple lab test can confirm the diagnosis. The creatinine level in the drained fluid is compared to the creatinine level in the blood. Creatinine is a waste product that concentrates in urine, so urine will have a much higher creatinine level than blood. A fluid creatinine level just 18% higher than the serum level can indicate a urine leak. In clinical practice, many centers use a ratio of 1.5 or higher as a practical threshold for pursuing further investigation.
Treatment Options
The goals of treatment are straightforward: drain the urinoma, stop the ongoing leak, and address whatever caused the problem in the first place.
Percutaneous drainage is the most common first step. A radiologist uses imaging guidance to insert a thin catheter through the skin directly into the urinoma, allowing the collected urine to drain out. This relieves pressure, reduces pain, and lowers the risk of infection. The catheter typically stays in place until the collection resolves.
Stopping the leak usually requires restoring normal urine flow. A ureteral stent, a thin flexible tube placed inside the ureter, can bridge a defect and allow urine to pass from the kidney to the bladder while the injured area heals. Most stents stay in for a few days to a few weeks, depending on how quickly healing progresses. If a tumor or chronic narrowing caused the obstruction, you may need a stent for months or longer, with replacement every three to six months.
In cases where stenting isn’t enough or isn’t possible, a percutaneous nephrostomy may be placed instead. This is a tube inserted through the back directly into the kidney, diverting urine into an external bag and taking all pressure off the damaged area. Antibiotics are commonly part of the treatment plan, especially if there are signs of infection in the collected fluid.
Small urinomas caught early sometimes resolve on their own once the underlying obstruction is cleared. Larger or infected collections almost always require active drainage.
What Happens If It’s Left Untreated
An untreated urinoma is not harmless. The collected urine is an ideal breeding ground for bacteria, and an infected urinoma can progress to an abscess. From there, the infection can spread to the bloodstream, potentially causing septic shock. Prolonged urine exposure irritates surrounding tissues, which can lead to fibrosis, a type of scarring that stiffens and damages nearby structures. Peritonitis, an infection of the abdominal lining, is another serious risk if urine spreads into the abdominal cavity.
Beyond infection, a growing urinoma can compress the kidney or ureter, worsening the original obstruction and further impairing kidney function. Electrolyte imbalances can also develop as the body reabsorbs components of the leaked urine from the surrounding tissue. Early diagnosis and treatment make a meaningful difference in avoiding these complications.