Urinary tract obstruction

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)

• Renal
  • Nephrolithiasis
  • Sloughed off renal papilla
  • Carcinoma of the renal pelvis
• Ureteropelvic junction obstruction
• Ureter
  • Intraluminal
    • Nephrolithiasis
    • Blood clots
  • Intramural
    • Ureteral stricture: a narrowing of the lumen of the ureter
      • Can be benign or malignant
      • Benign strictures often develop secondary to the healing of any intraluminal trauma caused by, e.g., surgical instrumentation (iatrogenic ureteral stricture) or infection
    • Accidental surgical ligation ^[1]
    • Ureteral carcinoma
  • Extraluminal
    • Pregnancy
    • Neoplasia: cervical, ovarian, colonic, etc.
    • 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)

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

• Bladder
  • Bladder carcinoma
  • Neurogenic bladder ^[2][3][4]
    • Two types of neurogenic bladder can cause BOO (and/or urinary retention). ^[3][4]
      • Spastic neurogenic bladder (upper motor neuron bladder): detrusor-sphincter dyssynergia
      • Flaccid neurogenic bladder (lower motor neuron bladder): detrusor areflexia but intact urethral sphincter innervation
• Urethra
  • Prostatic enlargement (benign prostatic hyperplasia or prostate cancer)
  • Congenital: posterior urethral valves
  • Stricture
  • Meatal stenosis
• Mechanical: 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 the elderly.

References:^{[1][2][3][4][5][6][7]}

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.

Urinary obstruction may be partial or complete, and unilateral or bilateral (in the case of upper UTO).
References:^[1][6][7][8]

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
  • 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
• Diagnosis
  • Ultrasound: hydronephrosis
  • IV urography: excludes vesicoureteral reflux and assesses ureteral patency
  • MAG3 renal radionucleotide scan
• 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

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:^[9][10]

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.

• Urinalysis: to detect the underlying pathology and exclude infection (proteinuria, hematuria , crystals , bacteriuria, pyuria, etc.)
• Urinary metabolites: elevated blood urea nitrogen and, in cases of bilateral UTO/UTO in a solitary kidney and elevated serum creatinine levels
• Serum electrolytes: hyperkalemia is a dangerous complication of kidney failure.
• Complete blood count
  • Leukocytosis in urinary tract infection
  • Anemia in chronic UTO ^[11]

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.

References:^{[1][6][7][8][12][13][14][15]}

General measures

• Analgesics (NSAIDs, IV morphine)
• Antibiotics: given prophylactically even in the absence of infection
• Nephroureterectomy: if the draining kidney is non-functional or in life-threatening urosepsis ^[16][17]

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.

• Upper UTO
  • Ureteral stenting
  • 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). ^[18]
• Lower UTO
  • Urethral catheterization with a Foley
  • Suprapubic catheterization if a Foley cannot be passed

Treatment of 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.
• Urothelial carcinoma: See “Treatment section” of “Urinary tract cancer.”
• 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

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

• 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 ^[2]
  • Intermittent self-catheterization
  • Lifestyle modifications
  • Spastic bladder: α-blockers (e.g., prazosin, tamsulosin)
  • Flaccid bladder: cholinergic medications
  • Urethral stenting, sphincterotomy, bladder augmentation, or urinary diversion as a last resort.
• Urethral stricture ^[19]
  • Short strictures: balloon dilatation, urethrotomy, urethral stent
  • Long strictures: urethroplasty
• Meatal stenosis: dilatation or meatoplasty

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

References:^{[2][16][17][18][19][20][21][22][23]}

Hydronephrosis

• Definition: dilation of the renal pelvis and calyces
• Etiology: dilation of the urinary tract occurs proximal to the site of the underlying pathology
  • Urinary tract obstruction (see “Etiology” above)
  • Urinary tract obstruction: e.g., due to retroperitoneal fibrosis (see also “Etiology” above)
  • Vesicoureteral reflux
  • Retroperitoneal fibrosis
• Clinical features
  • May be asymptomatic
  • Flank/back pain and/or abdominal pain
  • Oliguria
  • Fever and features of UTI if infected (pyonephrosis)
• Diagnosis
  • Ultrasound: hypoechoic dilation of the renal pelvis and calyces distending the healthy parenchyma ^[12]
  • Renal parameters (e.g., creatinine) may be elevated and might indicate renal failure (if bilateral obstruction is present or obstruction of a solitary kidney)
• Treatment: See the “Treatment” section above.
• Prognosis:
  • May be reversible in acute cases if the function is restored quickly
  • Chronic hydronephrosis or acute hydronephrosis that is not resolved expediently → ↑ intratubular pressure, compression of surrounding blood vessels → ↓ renal perfusion → ischemic 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 nonpregnant women with new-onset hydronephrosis!

Others

• Hydroureter: dilation of the ureter due to a distal obstruction
• Pyelonephritis and perinephric abscess
• Obstructive nephropathy; : This term refers to any renal impairment caused by urinary tract obstruction.
• Nephrolithiasis
• Bladder trabeculation and pseudodiverticula formation
• Acute renal failure

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

References:^[1][6][12]

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

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