Ureteral Obstruction
Ureteral obstruction is a blockage of the ureter—the tube that carries urine from the kidney to the bladder. It can affect one or both ureters and can be caused by many different conditions, including kidney stones, tumors within the ureter or bladder, external compression from other tumors or lymph nodes, strictures (narrowings) from prior injury or surgery, retroperitoneal fibrosis, blood clots, and congenital abnormalities. Ureteral obstruction can develop suddenly (as with a stone lodging in the ureter) or gradually (as with slowly progressive tumors or fibrosis). When urine cannot flow freely, the kidney’s collecting system swells (hydronephrosis), pressure builds, and, over time, kidney function can be affected. Evaluation and prompt treatment—directed at both relieving the obstruction and addressing the underlying cause—are important.
What is it?
The ureter is a muscular tube, about 25 to 30 centimeters long in adults, that carries urine from the kidney to the bladder. Each kidney has its own ureter, and the ureters normally propel urine downward using rhythmic muscular contractions (peristalsis). Ureteral obstruction refers to any blockage that impairs urine flow through the ureter. When urine cannot flow freely, the urine backs up above the blockage, causing the kidney’s collecting system (renal pelvis and calyces) to distend—a condition called hydronephrosis. If the ureter is also distended, it is called hydroureter. Pressure within the collecting system rises, and over time this pressure can affect kidney function.
Ureteral obstruction can be classified in several ways. Acute obstruction develops suddenly, over hours to days, and is most commonly caused by a kidney stone that has moved into and lodged within the ureter. Acute obstruction typically produces severe pain and other prominent symptoms. Chronic obstruction develops gradually over weeks to years and is often caused by slowly progressive processes such as tumors, retroperitoneal fibrosis, or strictures. Chronic obstruction may produce few symptoms until kidney function is significantly affected. Obstruction can be partial (some urine flow still occurs) or complete (no urine flow past the blockage). It can affect one ureter (unilateral) or both ureters (bilateral). Bilateral obstruction is much more serious in the short term because it affects both kidneys and can rapidly cause acute kidney injury.
Many conditions can cause ureteral obstruction. Kidney stones (urolithiasis) are the most common cause of acute unilateral obstruction, particularly in younger and middle-aged adults. Stones can lodge at natural narrowings of the ureter—typically at the ureteropelvic junction (where the renal pelvis meets the ureter), where the ureter crosses over the iliac vessels in the pelvis, or at the ureterovesical junction (where the ureter enters the bladder). Tumors within the ureter—most often upper tract urothelial carcinoma (transitional cell carcinoma)—are less common causes but important, particularly in older adults. Blood clots from bleeding within the urinary tract (from tumors, stones, procedures, or other causes) can also cause acute obstruction.
External compression is a common cause of chronic obstruction. This can include pelvic tumors (from the cervix, prostate, colon, rectum, ovary, uterus, or bladder), enlarged lymph nodes (from lymphoma, metastases, or other causes), aortic aneurysms, iliac artery aneurysms, and, in specific conditions, uterine changes during pregnancy. Retroperitoneal fibrosis is a condition of inflammatory scar tissue formation in the retroperitoneum that can encase and obstruct the ureters and may be idiopathic or associated with certain medications (such as ergot derivatives), IgG4-related disease, or other conditions. Endometriosis involving the urinary tract can also cause ureteral obstruction, most often in women of reproductive age.
Ureteral strictures (narrowings) from prior injury, prior surgery, prior radiation therapy, chronic inflammation, or previous stones can cause obstruction. Congenital abnormalities—such as ureteropelvic junction obstruction, ureterocele, or ectopic ureter—may present in childhood or, in some cases, adulthood. Iatrogenic injury during surgery (particularly gynecologic, colorectal, or urologic procedures) is a well-recognized cause of ureteral obstruction and may present acutely or with delayed symptoms.
Symptoms depend on the cause, whether obstruction is acute or chronic, and whether one or both ureters are affected. Acute obstruction—most classically from a stone—typically causes severe flank or back pain that comes in waves (renal colic) and may radiate to the abdomen, groin, testicle, or labia. Nausea and vomiting are common. Blood in the urine (visible or microscopic) frequently accompanies stone obstruction. Symptoms of urinary tract infection may be present, and infection combined with obstruction is a particularly serious combination. Chronic obstruction may produce fewer or vaguer symptoms, including dull flank discomfort, gradual reduction in urine output (particularly with bilateral obstruction), or symptoms of reduced kidney function such as fatigue, swelling, and changes in urination. Some cases are identified incidentally on imaging done for other reasons.
Diagnosis is based on clinical evaluation, laboratory testing, and imaging. CT is the primary imaging test in most cases. Non-contrast CT is highly sensitive for identifying stones and can also show hydronephrosis and other findings. CT urography (with dedicated contrast phases) provides detailed evaluation of the ureter and collecting system and is useful when tumors, strictures, or other soft tissue causes of obstruction are suspected. Ultrasound can identify hydronephrosis and is often used as an initial screening test or in patients who cannot undergo CT (such as pregnant women, in whom ultrasound and, when needed, MRI are preferred). MRI can be useful in specific situations. Nuclear medicine scans, particularly MAG3 with a diuretic challenge, can assess functional obstruction and split kidney function. Cystoscopy with retrograde imaging (in which contrast is injected up the ureter) is used in selected patients, particularly when imaging is inconclusive or when the diagnosis of an intrinsic ureteral lesion is being pursued.
Blood tests including complete blood count, kidney function (creatinine and eGFR), and electrolytes are important. Urine tests (urinalysis and culture) identify infection, blood, and other findings. Additional tests depend on the suspected underlying cause.
Important to Know
Management of ureteral obstruction depends on the cause, the severity and duration of obstruction, whether infection is present, whether one or both kidneys are affected, kidney function, and the patient’s overall health. Care is typically coordinated by emergency medicine clinicians (in acute presentations), urologists, interventional radiologists (for drainage procedures), nephrologists (when kidney function is significantly affected), and, when relevant, oncologists, gynecologists, general surgeons, and other specialists.
The first priority in many cases is to determine whether urgent drainage of the affected kidney is needed. Urgent drainage is generally indicated when there is infection combined with obstruction (which is a urologic emergency because of the risk of sepsis), significant impairment of kidney function (particularly with bilateral obstruction or in a solitary kidney), severe pain that cannot be controlled with medications, or other complications. Drainage can be accomplished in two main ways.
Ureteral stent placement, performed by a urologist through cystoscopy, involves inserting a thin, flexible tube through the bladder up the ureter to allow urine to flow past the obstruction. Ureteral stents can typically be placed relatively quickly and are often preferred for stones or short strictures.
Percutaneous nephrostomy, performed by an interventional radiologist under image guidance, involves inserting a drainage tube through the skin of the back directly into the kidney’s collecting system. This approach is often used when ureteral stent placement is not feasible (such as with severe obstruction that cannot be bypassed from below), in patients too unstable for cystoscopy, or when other factors favor this approach.
Both drainage methods relieve the obstruction and allow the kidney to function while the underlying cause is addressed. The choice between them depends on the specific clinical situation, available expertise, and patient factors.
Once drainage is established (when needed), treatment focuses on the underlying cause. For kidney stones, treatment depends on the stone’s size, location, and composition, and on the patient’s characteristics. Small stones (typically less than 5 mm) may pass on their own with pain control, hydration, and, in some cases, medical expulsive therapy (medications such as tamsulosin that may facilitate stone passage). Larger stones or those that do not pass spontaneously may require procedures such as ureteroscopy with laser lithotripsy (breaking up the stone with a laser through a small scope), shock wave lithotripsy (using external energy to fragment the stone), or, less commonly, percutaneous approaches or open surgery.
For urothelial tumors of the ureter or renal pelvis, treatment follows established principles for upper tract urothelial carcinoma, most often radical nephroureterectomy for high-risk disease, with kidney-sparing options for selected low-risk disease. For external compression from tumors elsewhere, treatment is directed at the primary cancer.
For retroperitoneal fibrosis, treatment often includes medical therapy with corticosteroids and, in selected patients, other immunosuppressive medications, along with drainage or surgical management when significant obstruction is present. IgG4-related disease and other underlying conditions are treated when identified.
For ureteral strictures, treatment options include endoscopic dilation or incision, ureteral stents, and, in some cases, surgical reconstruction. Long-term follow-up is important because strictures can recur.
For congenital causes such as ureteropelvic junction obstruction, surgical repair (pyeloplasty) is often the treatment of choice when meaningful function of the affected kidney is preserved and there is significant obstruction. Kidney-sparing endoscopic approaches may be considered in specific circumstances.
For iatrogenic ureteral injuries, treatment depends on the timing of recognition and the specific injury. Early recognition and appropriate repair by an experienced urologic surgeon offer the best chance of a good outcome.
For obstruction in pregnancy, management is individualized. Physiologic hydronephrosis of pregnancy (right-sided predominance, often mild) is common and does not require treatment. True obstruction, most often from stones, may require drainage with a ureteral stent or, in some cases, ureteroscopy. Coordination with obstetrics and, when appropriate, maternal-fetal medicine is important. Radiation exposure is minimized.
Care of kidney function is important throughout. Prolonged untreated obstruction can cause irreversible kidney damage, and prompt intervention preserves function. After obstruction is relieved, careful monitoring of kidney function and blood pressure is important. In some cases—particularly with prolonged severe obstruction—a phenomenon called postobstructive diuresis can occur, in which large volumes of urine are produced after the obstruction is relieved. This requires careful monitoring of electrolytes and fluid status.
Long-term follow-up depends on the underlying cause. For patients with a history of kidney stones, evaluation for stone type and metabolic factors (through 24-hour urine testing and blood tests) can guide preventive strategies. For patients with urothelial cancer, long-term surveillance is essential. For patients with strictures, retroperitoneal fibrosis, or congenital conditions, ongoing follow-up is important.
Care is typically coordinated by urologists and, when needed, interventional radiologists, oncologists, gynecologists, nephrologists, and other specialists. Imaging and laboratory findings are interpreted alongside the patient’s symptoms, examination, past medical history, and broader clinical context rather than in isolation.
Patient education plays an important role. Understanding the diagnosis, the specific cause when identified, the rationale for the treatment plan (including drainage when needed), the importance of follow-up, warning signs of recurrent obstruction or complications, and, when relevant, preventive measures for underlying conditions all contribute to better outcomes.
Red flag symptoms include severe flank or back pain not controlled by medications, high fever with chills (which combined with obstruction is a urologic emergency), signs of sepsis (severe illness, low blood pressure, rapid heart rate, confusion), significant decrease or absence of urine output (particularly if both kidneys may be affected or in a solitary kidney), significant blood in the urine with clots, severe nausea and vomiting with dehydration, severe abdominal pain, or rapid clinical deterioration. These warrant immediate emergency evaluation, as they may indicate obstructed infection, sepsis, or acute kidney injury requiring urgent drainage.