UTO Flashcards
A 60-year-old man presents with difficulty urinating, flank pain, and rising serum creatinine. What is the next best step if urinary tract obstruction is suspected?
A. Perform an abdominal CT scan without contrast.
B. Insert a bladder catheter.
C. Obtain a serum electrolyte panel.
D. Perform cystoscopy.
Answer: B. Insert a bladder catheter.
Rationale: Bladder catheterization is the first step to evaluate and relieve acute urinary retention, which can confirm the diagnosis and prevent further renal injury.
Which of the following physical exam findings is most suggestive of urinary tract obstruction (UTO)?
A. Costovertebral angle tenderness
B. Abdominal distention with bladder palpable above the pubic symphysis
C. Bilateral lower extremity edema
D. Hyperactive bowel sounds
Answer: B. Abdominal distention with bladder palpable above the pubic symphysis
Rationale: Palpable bladder distention suggests urinary retention due to obstruction, which may lead to UTO.
Abdominal ultrasonography in a patient with suspected UTO reveals hydronephrosis. Which of the following is a potential cause of a false-positive result?
A. Retroperitoneal fibrosis
B. Renal cysts
C. Staghorn calculi
D. Acute tubular necrosis
Answer: B. Renal cysts
Rationale: Renal cysts can mimic hydronephrosis on ultrasonography, leading to false-positive results.
False-positive results are associated with diuresis, renal cysts, or the presence of an extrarenal pelvis, a normal congenital
variant
Which of the following scenarios is most likely to result in a false-negative ultrasonography result in a patient with UTO?
A. Obstruction duration less than 48 hours
B. Volume expansion
C. Congenital ureteropelvic junction (UPJ) obstruction
D. Radiolucent urinary calculi
Answer: A. Obstruction duration less than 48 hours
Rationale: Hydronephrosis may not appear on ultrasound within the first 48 hours of obstruction or in cases of volume contraction.
Hydronephrosis may be absent on ultrasound when obstruction is <48 h in duration or associated with volume contraction,
staghorn calculi, retroperitoneal fibrosis, or infiltrative renal disease.
A 45-year-old man with suspected UTO has normal findings on ultrasonography. However, his symptoms persist, and renal function is deteriorating. What is the most appropriate next step?
A. Perform abdominal X-ray.
B. Perform a non-contrast CT scan.
C. Repeat ultrasonography with Doppler evaluation.
D. Perform a radionuclide renal scan.
Answer: B. Perform a non-contrast CT scan.
Rationale: Non-contrast CT is highly sensitive and specific for detecting urinary tract stones or other causes of obstruction when ultrasonography is inconclusive.
Which of the following is a key advantage of non-contrast CT in evaluating UTO?
A. Superior detection of contrast nephropathy
B. Ability to evaluate both intrinsic and extrinsic causes of obstruction
C. Higher sensitivity than ultrasound for hydronephrosis within 48 hours of obstruction
D. Superior to magnetic resonance urography in identifying retroperitoneal fibrosis
Answer: B. Ability to evaluate both intrinsic and extrinsic causes of obstruction
Rationale: Non-contrast CT is highly effective in visualizing both intrinsic (e.g., stones) and extrinsic (e.g., tumors, fibrosis) causes of obstruction and avoids the risks of contrast nephropathy in patients with renal impairment.
In which condition is VCUG most valuable?
A. Renal stone evaluation
B. Bilateral hydronephrosis
C. Vesicoureteral reflux
D. Retroperitoneal fibrosis
Answer: C. Vesicoureteral reflux
Rationale: VCUG is primarily used to diagnose vesicoureteral reflux and bladder neck or urethral obstructions.
Which of the following statements is most accurate regarding renal function recovery after obstruction relief?
A. Complete recovery is unlikely after 2 weeks of obstruction.
B. Partial recovery may occur after 1–2 weeks of complete obstruction.
C. Recovery is possible even after 8 weeks of complete obstruction.
D. Obstruction duration has little impact on renal function recovery.
Answer: B. Partial recovery may occur after 1–2 weeks of complete obstruction.
Rationale: While partial recovery of glomerular filtration rate (GFR) may occur after relief of obstruction lasting 1–2 weeks, recovery becomes unlikely after 8 weeks of complete obstruction.
What is the primary utility of a radionuclide scan after obstruction relief?
A. Detecting residual hydronephrosis
B. Predicting reversibility of renal dysfunction
C. Differentiating intrinsic from extrinsic obstruction
D. Diagnosing post-obstructive diuresis
Answer: B. Predicting reversibility of renal dysfunction
Rationale: A radionuclide scan performed after prolonged decompression can predict whether renal function recovery is likely.
What is the recommended approach when the reversibility of renal dysfunction is uncertain after prolonged obstruction?
A. Delay decompression until diagnostic confirmation of reversibility
B. Perform immediate decompression to maximize chances of recovery
C. Use imaging to assess irreversibility and avoid decompression
D. Monitor for spontaneous resolution of obstruction
Answer: B. Perform immediate decompression to maximize chances of recovery
Rationale: In the absence of definitive evidence of irreversibility, every effort should be made to decompress the obstruction promptly, as this increases the chances of at least partial recovery of renal function.
Which duration of complete obstruction is most likely associated with irreversible renal damage?
A. 2–3 days
B. 1–2 weeks
C. 4–6 weeks
D. >8 weeks
Answer: D. >8 weeks
Rationale: Prolonged obstruction lasting more than 8 weeks is typically associated with irreversible renal damage, whereas shorter durations (1–2 weeks) may still allow for partial recovery.
Which of the following is LEAST likely to contribute to postobstructive diuresis?
A. Osmotic diuresis due to urea excretion
B. Suppressed antidiuretic hormone (ADH) levels
C. Increased salt and water reabsorption in the tubules
D. Correction of extracellular volume expansion
Answer: C. Increased salt and water reabsorption in the tubules
Rationale: In postobstructive diuresis, there is decreased salt and water reabsorption due to tubular dysfunction, along with osmotic diuresis, suppressed ADH levels, and the correction of extracellular volume expansion.
What is the most likely electrolyte disturbance in a patient with severe post obstructive diuresis and inadequate fluid replacement?
A. Hyperkalemia
B. Hyponatremia
C. Hypernatremia
D. Hypophosphatemia
Answer: C. Hypernatremia
Rationale: Excessive loss of electrolyte-free water in the urine, combined with inadequate fluid replacement, can result in hypernatremia.
What is the best initial fluid replacement strategy for a patient with post obstructive diuresis and hypernatremia?
A. 0.9% saline in amounts exceeding urinary losses
B. 0.45% saline guided by serum and urine electrolyte measurements
C. Intravenous dextrose without electrolytes
D. Ringer’s lactate at a fixed rate
Answer: B. 0.45% saline guided by serum and urine electrolyte measurements
Rationale: In the setting of hypernatremia and significant urinary losses, replacement with 0.45% saline is appropriate to address free water deficits while monitoring serum and urine electrolytes.
A patient develops postobstructive diuresis after relief of bilateral ureteral obstruction. Their urine sodium and potassium levels are low, and serum sodium is 150 mEq/L. What is the most appropriate next step?
A. Restrict fluid intake
B. Administer intravenous 0.45% saline
C. Start diuretics to prevent hypervolemia
D. Administer intravenous 0.9% saline
Answer: B. Administer intravenous 0.45% saline
Rationale: The patient has hypernatremia due to loss of electrolyte-free water in urine. Administering 0.45% saline replaces the free water deficit while addressing ongoing losses.
