Urinary tract obstruction

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) ^[1][2]

Renal obstruction

• Nephrolithiasis
• Carcinoma of the renal pelvis
• Ureteropelvic junction obstruction
• Renal papillary necrosis

Ureteral obstruction

• Intraluminal
  • Nephrolithiasis
  • Blood clots
• Intramural: The pathology lies within the ureteric wall.
  • Ureteral stricture: a narrowing of the lumen of the ureter
    • Primary or metastatic malignant strictures ^[3]
    • Benign strictures from iatrogenic intraluminal trauma (e.g., caused by surgical instrumentation) or infection
  • Ureteral carcinoma
  • Accidental surgical ligation ^[4]
• Extraluminal: extrinsic compression of the ureter by adjacent organs or structures
  • Pregnancy
  • Neoplasia: e.g., cervical, ovarian, colonic
  • Aortic aneurysm
  • Iliac artery aneurysm
  • Tubo-ovarian masses: endometriosis, prolapse, hematomas
  • Gastrointestinal masses: Crohn disease, diverticulitis
  • Retroperitoneal fibrosis (Ormond disease)
  • Iatrogenic: injury to the ureter during surgery (e.g., gynecological procedures)
• Ectopic ureter
• Ureterocele

Lower urinary tract obstruction (bladder outlet obstruction) ^[1][2]

Bladder obstruction

• Bladder carcinoma
• Neurogenic bladder ^[5][6][7]
• Urinary bladder tamponade: acute bladder outlet obstruction due to a blood clot at the internal urethral orifice ^[8][9]
  • Caused by bleeding cancer, bladder trauma, surgery (e.g., TURP), hemorrhagic cystitis, or anticoagulant-induced bleeding
  • Patients may complain of preceding hematuria followed by acute urinary retention.
• Bladder calculi
• Bladder neck dysfunction

Urethral obstruction

• Prostatic enlargement (e.g., due to benign prostatic hyperplasia or prostate cancer)
• Posterior urethral valves (congenital)
• 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. ^[1]

Overview

• Clinical features depend on the etiology, location, degree, and duration of obstruction.
• Features range from oliguria or anuria to incidentally diagnosed asymptomatic hydronephrosis.

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

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.

Hydronephrosis ^[11]

• Overview
  • Dilation of the renal pelvis and calyces
  • Occurs proximal to the site of the underlying pathology
  • Hydroureter: dilation of the ureter due to a distal obstruction
• Classification: grade I–IV based on severity
• Etiology
  • Urinary tract obstruction, e.g., due to retroperitoneal fibrosis or bladder obstruction
  • Vesicoureteral reflux
• Typical findings
  • May be asymptomatic if isolated
  • Symptoms depend on the etiology and associated conditions, e.g.:
    • Flank and back pain and/or abdominal pain
    • Oliguria
    • Fever and features of a UTI, if present (pyonephrosis)
• Diagnosis
  • Ultrasound: anechoic dilation of the renal pelvis and calyces with distention of the healthy parenchyma ^[12]
  • Creatinine: elevation indicates renal failure (in bilateral obstruction, or unilateral obstruction in patients with a solitary kidney)
• Prognosis
  • 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.

Urethral stricture

• Definition: narrowing of the urethra with possible restriction of urinary flow
• Etiology
  • Traumatic or iatrogenic (instrumentation/catheterization)
  • Post-infectious (e.g., urethritis)
  • Congenital
  • Idiopathic
• Clinical features ^[13]
  • May be asymptomatic until manifesting with acute urinary retention
  • Symptoms of bladder outlet obstruction
    • Feeling of incomplete bladder emptying
    • Weak stream
    • Straining to urinate
  • Genitourinary pain
  • Urinary tract infections
  • Ejaculatory dysfunction
• Diagnostics
  • Uroflowmetry: plateau-shaped uroflow curve
  • Retrograde urethrography/voiding cystourethrography: visualizes urethral strictures
  • Cystourethroscopy: to measure the extent of stenosis
• Treatment
  • 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 ^[14][15]

• Definition: : ureteral stenosis at the junction of the renal pelvis and the ureter
• Etiology
  • Congenital
    • Intrinsic: malformation of the smooth muscle of a ureteral segment and consecutive impairment of peristalsis (functional stenosis)
    • Extrinsic: aberrant renal pole artery causing proximal ureteral obstruction
  • Acquired: factors causing ureteral obstruction (see “Etiology” above)
• Clinical features
  • Newborns and infants
    • Palpable upper abdominal mass
    • Failure to thrive
    • Recurrent pyelonephritis
  • Children and adults
    • Flank pain or upper abdominal pain that may be triggered or worsened during states of increased diuresis (e.g., after caffeine or alcohol consumption).
    • Nausea/vomiting
    • Recurrent pyelonephritis
    • Hematuria
• Diagnostics
  • Ultrasound: hydronephrosis
  • IV urography: excludes vesicoureteral reflux and assesses ureteral patency
  • Functional renal scintigraphy
• Treatment
  • Observation: asymptomatic, mild cases
  • Surgery
    • Symptomatic patients or those with > 40% loss of renal function
    • Anderson-Hynes pyeloplasty: open or laparoscopic resection of the obstructed segment and anastomosis of the ureter to the remaining renal pelvis

Approach

• Perform an initial assessment.
  • History and physical examination: to identify clinical features of UTO and clues to the cause of UTO
  • Bedside postvoid residual: bladder ultrasound, bladder scanner, or bladder catheterization to rule out lower UTO
  • Laboratory studies: urinalysis, BMP, and CBC
  • Imaging: renal and urinary tract ultrasound
• Consider further studies based on the suspected underlying cause of UTO.
• Consult urology early.
• See also “Diagnosis of urinary retention” and “Diagnostics” in “Hydronephrosis.”

Do not delay relieving pressure on the urinary tract during the diagnostic workup. Perform bladder catheterization or consult urology for upper urinary tract interventions as indicated. ^[11]

Consider screening patients with unexplained AKI for upper UTO using renal and urinary tract ultrasound.

Laboratory studies ^[1][16]

• Urinalysis
  • Bacteriuria, pyuria: may indicate UTI
  • Hematuria: may indicate UTI, malignancy, or nephrolithiasis
• BMP
  • ↑ BUN; , ↑ creatinine levels
  • Hyperkalemia, acidosis: may indicate renal insufficiency
• CBC
  • Leukocytosis: may indicate UTI
  • Anemia: acute (e.g., in blood loss) or chronic (e.g., in malignancy, CKD) ^[17]

Consider further studies (e.g., urine and blood cultures for suspected UTI) based on initial findings.

Imaging ^[1][18]

Routine studies

Typical findings include hydronephrosis, hydroureter, and perinephric fluid.

• 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
  • Preferred for suspected nephrolithiasis: Stones are usually opaque; density depends on their composition.
  • Also indicated if ultrasound is inconclusive
• Kidney, ureter, and bladder x-ray
  • Not commonly used
  • May detect hydronephrosis or urolithiasis
• MRI: may be used if there are contraindications to CT or for surgical planning

Specialized studies

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
• Retrograde pyelography: to confirm a diagnosis of ureteropelvic junction obstruction
• Renal scintigraphy: to evaluate kidney function and predict recovery following relief of the UTO
• Cystoscopy: gold-standard diagnostic study for bladder cancer
• Voiding cystourethrography: to evaluate for vesicoureteral reflux
• Urodynamic studies: 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 ^[11][18][19]

• 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 ^[20]
• Provide supportive care for urinary tract obstruction.

Nephroureterectomy may be performed if the involved kidney is nonfunctional. ^[21]

Management of lower UTO ^[22][23]

• Initiate treatment of urinary retention (bladder catheterization).
• Provide supportive care for urinary tract obstruction.
• Monitor for postobstructive diuresis.

Supportive care for urinary tract obstruction

• Analgesics ^[24][25]
  • NSAIDs, e.g., ketorolac
  • Opioids, e.g., morphine
• Consider antibiotic prophylaxis, e.g., prior to invasive procedures. ^[18]

Treatment of the underlying cause

See “Etiology of urinary tract obstruction” and the respective articles (e.g., benign prostatic hyperplasia) for details. See “Treatment of urinary retention” for the management of functional obstruction.

• 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).
• Urinary bladder tamponade
  • Insert a three-way Foley catheter.
  • Perform continuous bladder irrigation to dissolve blood clots.
  • Consult urology for definitive management.
• Ureteral stricture: Stricture length is predictive of outcome after treatment.
  • Transluminal balloon dilation with or without stent placement: for short, nonischemic strictures
  • Endoureterotomy
    • After unsuccessful balloon dilation
    • For all types of strictures except short, nonischemic strictures
  • Laparoscopic or open surgery: if balloon dilation and endoureterotomy are unsuccessful
• Urothelial carcinoma: See “Treatment” in “Urinary tract cancer.”
• Meatal stenosis: dilatation or meatoplasty
• Pregnancy
  • Asymptomatic with no infection: expectant management; most UTOs will resolve spontaneously after delivery
  • Presence of infection: See “UTI in pregnancy.”

Disposition ^[23]

• Consider admission for patients with neurological deficits, refractory pain, upper UTO, or complications of UTO (e.g., urosepsis, AKI).
• Stable patients with lower UTO: After bladder decompression, consider discharge with an indwelling catheter for outpatient urology follow-up.

• Pyelonephritis and perinephric abscess
• Obstructive nephropathy: renal impairment caused by UTO
• Nephrolithiasis
• Bladder trabeculation and pseudodiverticula formation
• Acute kidney injury

UTO increases the risk of urolithiasis and UTIs progressing to urosepsis.

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