Urinary tract obstruction (UTO) is a mechanical or functional blockage that inhibits the outflow of urine. Any part of the urinary tract can be affected by UTO. The etiology of UTO may be congenital, neoplastic, or inflammatory; additional etiologies include certain neurological conditions and stones. A UTO may be partial or complete and unilateral or bilateral. The clinical features of UTO depend on the etiology, location, degree, and duration of obstruction. Patients with chronic UTO are often asymptomatic until they develop complications (e.g., urinary tract infections, renal failure). The initial evaluation of UTO includes ultrasound and laboratory studies (CBC, BMP, urinalysis). In some cases, further urinary tract imaging may be carried out to provide additional diagnostic information. Treatment depends on the site and degree of obstruction and the presence of infection. Complete UTO is a medical emergency and must be treated promptly with bladder catheterization, ureteral stenting, or percutaneous nephrostomy.
Upper urinary tract obstruction (supravesicular urinary tract obstruction) 
- Blood clots
- Intramural: The pathology lies within the ureteric wall.
Extraluminal: extrinsic compression of the ureter by adjacent organs or structures
- Neoplasia: e.g., cervical, ovarian, colonic
- Aortic aneurysm
- Iliac artery aneurysm
- Tubo-ovarian masses: endometriosis, prolapse, hematomas
- Gastrointestinal masses: Crohn disease, diverticulitis
- (Ormond disease)
- Iatrogenic: injury to the ureter during surgery (e.g., gynecological procedures)
Lower urinary tract obstruction (bladder outlet obstruction) 
- Bladder carcinoma
- Neurogenic bladder 
- (blood clot at internal urethral meatus)
- Bladder calculi
- Bladder neck dysfunction
- Prostatic enlargement (e.g., due to or )
- Urethral stricture
- Urethral carcinoma
- Meatal stenosis
- Kinked or plugged indwelling catheter
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 older adults. 
- Clinical features depend on the etiology, location, degree, and duration of obstruction.
- Features range from oliguria or anuria to incidentally diagnosed asymptomatic hydronephrosis.
|Clinical features of urinary tract obstruction|
|Upper (supravesical) UTO||Lower (infravesical) UTO|
Urinary obstruction may be partial or complete and unilateral or bilateral (in the case of upper UTO).
- Classification: grade I–IV based on severity
- Typical findings
- Kidney damage may be reversible if urinary flow is restored quickly.
- Chronic hydronephrosis or acute hydronephrosis that is not resolved expediently →; ↑ intratubular pressure and compression of surrounding blood vessels → ↓ renal perfusion → ischemic tubular atrophy, thinning of the renal cortex and medulla, and irreversible loss of renal function
Always consider gynecologic malignancies (e.g., cervical, uterine, ovarian) in nonpregnant women with new-onset hydronephrosis.
Subtypes and variants
- Definition: narrowing of the urethra with possible restriction of urinary flow
- Clinical features 
- Internal urethrotomy: endoscopic transurethral approach; incision at 12 o'clock position to release strictures/scar tissue
- Urethroplasty: open reconstruction with excision of the fibrotic urethra and reanastomosis ; indicated if urethrotomy fails
- Permanent urethral stents: placed endoscopically; indicated in patients with short-length strictures
Ureteropelvic junction obstruction 
- Definition: : ureteral stenosis at the junction of the renal pelvis and the ureter
- Newborns and infants
- Children and adults
- Perform an initial assessment.
- Consider further studies based on the suspected underlying cause of UTO.
- Consult urology early.
- See also “ ” and “Diagnostics” in “ .”
Laboratory studies 
Renal and urinary tract ultrasound
- Best initial test for most patients with undifferentiated UTO
- Modality of choice for pregnant individuals and children
- CT abdomen and pelvis
- Kidney, ureter, and bladder x-ray
- MRI: may be used if there are contraindications to CT or for surgical planning
Consider the following studies under specialist guidance for further evaluation of specific suspected causes or if initial testing is inconclusive. See “Imaging techniques in urology” for details.
- Intravenous pyelography (IVP): to determine the degree of hydronephrosis and localize the obstruction
- ureteropelvic junction obstruction : to confirm a diagnosis of
- kidney function and predict recovery following relief of the UTO : to evaluate
- bladder cancer : gold-standard diagnostic study for
- vesicoureteral reflux: to evaluate for
- : to evaluate for neurogenic bladder
UTO accompanied by acute kidney injury, signs of sepsis, refractory pain, dehydration (due to nausea and vomiting), or anuria (suggesting complete UTO) is a medical emergency. Prompt drainage of the urinary tract is indicated to prevent severe complications.
Management of upper UTO 
- Consult urology for definitive management.
- Ureteral stenting: to drain fluid from the renal pelvis into the bladder
- Percutaneous nephrostomy: if a ureteral stent cannot be placed or patients have complete UTO and concomitant infection 
- Provide .
Nephroureterectomy may be performed if the involved kidney is nonfunctional. 
Management of lower UTO 
- Initiate treatment of urinary retention.
- Provide supportive care for urinary tract obstruction.
- Monitor for postobstructive diuresis.
Supportive care for urinary tract obstruction
- Analgesics 
- Consider antibiotic prophylaxis, e.g., prior to invasive procedures. 
Treatment of the underlying cause
- Nephrolithiasis: : Management includes conservative therapy; and/or procedures to enhance stone expulsion or removal; , e.g., shock wave lithotripsy; , ureteroscopy (See “Treatment of nephrolithiasis” for details).
- Neurogenic bladder 
- Bladder neck dysfunction: alpha blockers and/or cystoscopic bladder neck incision
Ureteral stricture: Stricture length is predictive of outcome after treatment.
- Transluminal balloon dilation with or without stent placement: for short, nonischemic strictures
- After unsuccessful balloon dilation
- For all types of strictures except short, nonischemic strictures
- Laparoscopic or open surgery: if balloon dilation and endoureterotomy are unsuccessful
- : See “Treatment” in “ .”
- Meatal stenosis: dilatation or meatoplasty