• Clinical science

Urinary tract obstruction (Obstructive uropathy)

Abstract

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, urothelial 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).

Etiology

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!

References:[1][2][3][4][5][6][7][8]

Clinical features

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.

Upper (Supravesical) UTO Lower (Infravesical) UTO
Acute obstruction
  • Renal/ureteric colic (ipsilateral, severe, colicky flank pain that might occur only during urination)
  • Hematuria
  • Nausea and vomiting
  • Oliguria or anuria (rare)
  • Clinical signs of inflammation (i.e., fever and chills → suspicious for urosepsis)
Chronic obstruction

Urinary obstruction may be partial or complete, and unilateral or bilateral (in the case of lower UTO)!
References:[6][7][8][2][9]

Subtypes and variants

Ureteropelvic junction obstruction

  • 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 presentation
  • Diagnosis
  • Treatment
    • Observation: asymptomatic, mild cases
    • Surgery: symptomatic patients or those with > 40% loss of renal function

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!References:[10]

Diagnostics

Laboratory tests

Laboratory tests can be used to aid in the detection of the 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.

Imaging study Indications Findings
Ultrasound
  • Best initial test for most patients as it is inexpensive and does involve radiation exposure. Not as sensitive as CT in detecting stones but can detect stones > 3 mm.
CT
  • 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
  • Urolithiasis: Stones are usually opaque; density depends on their composition.
  • Hydronephrosis: dilation of the urinary tract proximal to the site of obstruction
KUB x-ray
  • Can be useful in diagnosing patients with hydronephrosis and in most patients with nephrolithiasis. X-ray will not detect calcium stones < 3 mm or radiolucent stones.
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
  • 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.
MRI
  • 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.
Voiding cystourethrography
  • First-line imaging study to diagnose patients with suspected vesicoureteral reflux (VUR). Should be performed in any child with 2 or more febrile UTIs, or any child with the combination of one febrile UTI and either renal anomalies on ultrasound, a fever of > 102.2°F and a causal microbe other than E. coli found on culture, or elevated blood pressure and poor growth/failure to thrive. Also the first-line modality for diagnosing posterior urethral valves (PUV).
  • VUR: visualization of retrograde urine flow back into the ureter when voiding
  • PUV: dilated, elongated, posterior urethra when voiding without a catheter
Cystoscopy
Urodynamic studies

References:[11][7][2][8][12][13][14][6][15][9]

Treatment

  1. General measures
  2. Relieve 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.
    • Upper UTO: Ureteral stenting or percutaneous nephrostomy is indicated if a ureteral stent cannot be placed as well as in patients with complete/severe UTO and a concomitant infection (a medical emergency).
    • Lower UTO: urethral catheterization with a Foley, or suprapubic catheterization if a Foley cannot be passed
  3. Once acute, complete obstruction has been managed, treat the underlying cause
    • Upper UTO
      • Nephrolithiasis: Conservative management with pain control and pharmacologic aids for stone passage (alpha blockers, calcium channel blockers) is often sufficient.
        • Urological intervention is appropriate for patients with stones > 10 mm; serious clinical symptoms such as vomiting, anuria, and intolerable pain; signs of renal failure or sepsis; or if the patient fails to pass the stone after 4–6 weeks.
          • Shock wave lithotripsy (SWL): first-line stone removal intervention
          • Ureteroscopy: first-line stone removal intervention; more effective than SWL but has higher complication rates. The technique may be more appropriate for harder stones or stones > 1.5 cm.
          • Percutaneous nephrolithotomy: may also be considered in patients with harder or larger stones, or in patients with refractory stones
          • Laparoscopic stone removal: for refractory stones
          • Open surgical removal: rarely required.
      • Papillary necrosis: hydration, urine alkalinization, targeted antibiotic therapy if concurrent infection. Nephrectomy may be warranted if the concurrent infection is severe. As papillary necrosis is usually bilateral, patients may progress to dialysis-dependent renal failure.
      • Urothelial carcinoma: See treatment section of urothelial carcinoma.
      • Ureteral stricture: The length of the stricture is the most predictive factor of outcome after treatment.
        • Transluminal balloon dilation with or without stent placement: ideal for short, nonischemic strictures
        • Endoureterotomy: overall success higher than with balloon dilation rates; more frequently used for all other types of strictures or if balloon dilation fails
        • Laparoscopic or open surgery: used if the minimally invasive measures above fail
      • Pregnancy
        • Asymptomatic patients with no infection: observation; most will resolve spontaneously after delivery
        • Presence of infection: antibiotics, hydration, and ureteric stenting. Rarely, there is an obstruction significant enough to require percutaneous nephrostomy.
      • Intra-abdominal mass
        • Manage the respective malignancy. Ureteral stenting or nephrostomy tubes may be indicated for decompression.
      • Abdominal aortic aneurysm: surgical excision and repair
    • Lower UTO
      • Bladder calculi
        • Removal of the stone
          • Transurethral cystolitholapaxy
          • Percutaneous cystolitholapaxy: allows use of shorter and wider tools, as they no longer need to fit in the urethra
          • Open suprapubic cystostomy: removal of intact stones; used for multiple, large, hard stones or stones that adhere to the bladder mucosa
        • Alkalinization of urine to pH > 6.5 with potassium citrate may dissolve stones, but removal should be attempted in all but medically unstable or near-terminal patients.
      • Bladder neck dysfunction: α-blockers and/or cystoscopic incision of the neck of the bladder
      • Neurogenic bladder
      • Urethral stricture
        • Short strictures: balloon dilatation, urethrotomy, urethral stent
        • Long strictures: urethroplasty
      • Meatal stenosis: dilatation or meatoplasty
      • Phimosis: circumcision

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!

References:[7][16][17][18][19][20][21][22][23][24][3][25]

Complications

Hydronephrosis

  • Definition: dilation of the renal pelvis and calyces
  • Etiology
  • Clinical features
  • Diagnosis
    • Ultrasound: hypoechoic dilation of the renal pelvis and calyces distending the healthy parenchyma
    • Renal parameters (e.g., creatinine) may be elevated → signs of renal failure possible (especially if bilateral obstruction is present)
  • Differential diagnoses for hydronephrosis
    • Parapelvic cyst
    • Ampullary type of renal pelvis
    • Megacalycosis
  • Treatment
    • See the treatment algorithm above: analgesics and prophylactic antibiotics; decompression with ureteral stenting, percutaneous nephrostomy, urethral catheterization, or suprapubic catheterization if the patient meets criteria above, or if the hydronephrosis is severe and bilateral (or affects a solitary kidney), as this could rapidly lead to renal failure. Once acute issues resolve, treat the underlying cause.
  • Prognosis:
    • May be reversible in acute cases if function is restored quickly
    • Chronic hydronephrosis or acute hydronephrosis that is not resolved expediently → ↑ intratubular pressure, compression of surrounding blood vessels → ↓ renal perfusionischemic tubular atrophy, thinning of renal cortex and medulla, irreversible loss of renal function

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

Grade Finding
I
  • Dilation of the renal pelvis without dilation of the calyces
II
III
  • Moderate dilation of the renal pelvis, calyces, and fornices
  • Beginning parenchymal compression from a dilated renal pelvis
IV
  • Severe dilation of the renal pelvis causing complete parenchymal compression

Others

Urinary obstruction increases susceptibility to urolithiasis and urinary tract infections that may progress to urosepsis!
References:[6][7][2][26][13]

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