Urinary tract obstruction

Last updated: March 23, 2022

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Urinary tract obstruction (UTO) is a mechanical or functional block to the outflow of urine that can affect any part of the urinary tract. The obstruction may be partial or complete, unilateral or bilateral, and upper (supravesical) or lower (infravesical). The etiology may be intraluminal (urolithiasis), intramural (strictures, tumors), extraluminal (extrinsic compression from an adjacent tumor/aneurysm/uterus), or functional (neurogenic bladder). The presentation of UTO depends on the site, degree, and duration of obstruction and may be acute (flank pain, urinary retention, etc.) or chronic. Patients with chronic UTO are often asymptomatic until they develop complications (urinary tract infections, renal failure) or are diagnosed incidentally with uremia and/or sonographic evidence of hydronephrosis. Urinary tract CT scan, IV pyelography, cystoscopy, and renal radionucleotide scans provide additional diagnostic information, if necessary. Treatment depends on the site and degree of obstruction and the presence of infection. Complete obstruction with infection is an emergency and must be treated promptly with IV antibiotics and nephrostomy (for upper UTO) or suprapubic cystostomy (for lower UTO). Definitive treatment of the UTO depends on the cause (e.g., α-blockers for small stones, ureteric dilatation for ureteric strictures, TURP for BPH).

Upper urinary tract obstruction (supravesical urinary tract obstruction)

Lower urinary tract obstruction (bladder outlet obstruction, or BOO)

The most common etiology of UTO is dependent on age: congenital anomalies (e.g., posterior urethral valves) in children, nephrolithiasis in young adults, and prostatic enlargement (BPH and prostate cancer) in the elderly.


Clinical features depend on the etiology, location, and duration of obstruction. Patients range from having oliguria/anuria to only having asymptomatic hydronephrosis that is incidentally identified through imaging or elevated creatinine levels.

Clinical features of urinary tract obstruction
Upper (supravesical) UTO Lower (infravesical) UTO
Acute obstruction
Chronic obstruction

Urinary obstruction may be partial or complete, and unilateral or bilateral (in the case of upper UTO).

Ureteropelvic junction obstruction

Patients with a UTO may be asymptomatic. It may be an incidental finding on ultrasound or become apparent through a rise in creatinine levels seen on routine blood work!

Laboratory tests

Laboratory tests can be used to aid in the detection of obstructive etiology and test for possible complications, such as infection or blood and electrolyte abnormalities.

Imaging modalities

Imaging studies can be used to demonstrate hydronephrosis and identify an obstructive cause, if one exists. The imaging modality of choice will depend on the most likely etiology based on the individual patient's clinical presentation. In general, ultrasound is the ideal initial imaging study if the patient has had no prior imaging, as it is an inexpensive, non-invasive, and high-yield screening tool.

Overview of imaging modalities for diagnosing urinary tract obstruction
Imaging study Indications Findings
  • Best initial test for most patients as it is inexpensive and does not involve radiation exposure. Not as sensitive as CT in detecting stones but can detect stones > 3 mm. [7]
  • The best initial imaging study in cases of suspected nephrolithiasis. CT is also indicated if a patient's prior ultrasound findings are inconclusive.
  • Also useful in imaging obstruction due to intestinal or gynecological malignancy
KUB x-ray
Intravenous pyelography (IVP)
  • Used less frequently. It can be used to diagnose the degree of hydronephrosis and location of obstruction in patients with signs of hydronephrosis on prior imaging but no visualized cause or locus of obstruction on ultrasound, x-ray, or CT.
Retrograde pyelography
  • Used to confirm a diagnosis of ureteropelvic junction (UPJ) obstruction and to characterize the obstruction for interventional planning. May also be indicated to better visualize the location of an obstruction (due to a stone, tumor, etc.) if prior imaging is insufficient.
  • Additionally used in patients who would benefit from but cannot undergo an IVP conducted due to a contraindication to IV contrast [15]
  • Filling defect at the level of the obstruction
Renal radionucleotide scan
  • Used to evaluate kidney function and predict the degree of expected functional recovery following removal of the UTO
  • Nonvisualization is indicative of a poor prognosis.
  • This is not a first-line imaging modality for UTO, and it is not useful in imaging stones. It may have some utility in imaging specific sections of the kidney for surgical planning. [8]
Voiding cystourethrography
  • VUR: visualization of retrograde urine flow back into the ureter when voiding
  • PUV: dilated, elongated, posterior urethra when voiding without a catheter
Urodynamic studies


General measures

Decreasing the pressure in the collecting system

Urologic emergencies necessitating urgent intervention include complete UTO; obstruction severe enough to cause renal failure; obstruction with concomitant infection or fever, refractory pain, or dehydration due to nausea and vomiting.

Treatment of the underlying cause

Upper UTO

Lower UTO

See benign prostatic hyperplasia, prostate cancer, posterior urethral valves, urethral carcinoma, retroperitoneal fibrosis, ureterocele, and ectopic ureter for further treatment principles.

An acute complete obstruction or chronic partial obstruction with evidence of infection, renal failure, or urinary retention requires emergent treatment.



Women with gynecological malignancies may present with hydronephrosis. Cervical, uterine, and ovarian cancers should therefore always be considered in nonpregnant women with new-onset hydronephrosis!


Urinary obstruction increases susceptibility to urolithiasis and urinary tract infections that may progress to urosepsis!


We list the most important complications. The selection is not exhaustive.

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