Urinary Tract Obstruction

Urinary Tract Obstruction

• Restricted flow of urine from the kidneys through the urinary tract to the external urethral orifice.
• Common cause of acute and chronic renal failure.
• Potentially curable form of kidney disease.

Definition of Terms

• No data available in unselected populations.
• 20-35% prevalence in large survey among elderly men.
• 3.8% (adults); 2.0% (children) postmortem examinations.
• No gender difference until 20 years.

Age

• Women: 20-60 years.
• Men: >60 years.
• Special consideration in pediatric patients.

Etiology

• Mechanical blockade.
• Foundation defects.
• Normal points of narrowing include:
  • Ureteropelvic junction.
  • Ureterovesical junction.
  • Bladder neck.
  • Urethral meatus.
• Congenital malformations:
  • Narrowing of the ureteropelvic junction.
  • Anomalous (retrocaval) location of the ureter.
• Acquired defects:
  • Pelvis tumor.
  • Calculi.
  • Urethral stricture.
• Infectious causes:
  • Schistosoma haematobium.
  • Genitourinary tuberculosis.
• Other causes:
  • Obstructive uropathy.
  • Extrinsic neoplastic.
  • Inflammatory disorders.
  • Retroperitoneal fibrosis.

Pathophysiology

• Unilateral (UUO) and bilateral (BUO) obstruction.
• Obstruction relieved or not.
• Time of obstruction.

Clinical Features

• Pain.
• Impaired excretory function.
• Bladder outlet obstruction.
• Bilateral renal pelvic or ureteric obstruction.
• Solitary functioning kidney.
• Hypertension.

Diagnosis

• Pain, renal colic.
• Inability to void effectively.
• Alteration in pattern of micturition.
• Recurrent UTI.
• New-onset or poorly controlled hypertension.
• Polycythemia.
• Recent gynecologic or abdominal surgery.

Physical Examination

• Signs of dehydration and intravascular volume depletion.
• Peripheral edema.
• Hypertension.
• Signs of congestive heart failure.
• Palpable kidney or bladder.
• Enlargement of pelvic organs.
• Examination of external urethra for phimosis, meatal stenosis.

Diagnostic Imaging

• Renal US:
  • Safe in pregnant and pediatric patients.
  • No need for IV contrast.
  • May have false negative in acute obstruction (35%).
  • Doppler measures renal resistive index (RI).
• Excretory Urography:
  • Limited use in patients with renal insufficiency.
  • Increased risk of contrast-induced nephropathy.
• Whitaker Test:
  • Invasive.
  • Discordant results limit clinical usefulness.
  • Normal: <15 cm H20.
  • Indeterminate: 15-22 cm H20.
  • Obstruction: >22 cm H20.
• Nuclear Renography:
  • Normal: T ½ < 10 min.
  • Indeterminate: T ½ 10-20 min.
  • Obstructed: T ½ > 20 min.
• CT:
  • Most accurate study to diagnose ureteral calculi.
  • More sensitive to identify cause of obstruction.
  • Helpful in surgical planning.
• MRI:
  • Can identify hydro but unable to identify calculi and ureteral anatomy of unobstructed systems.
  • Diuretic MRU can demonstrate obstruction, especially accurate with strictures or congenital abnormalities.
  • IV gadopentetate-DTPA allows functional assessment of collecting system while providing anatomic detail.
  • GFR assessment.
  • Renal clearance.
  • Still several limitations in its use.