Chapter 28-15: Urinary Tract Obstruction

TEXTBOOK PRESENTATION

Symptoms vary with site, degree, and rapidity of onset of the obstruction. Obstruction may cause pain if acute or may be painless if chronic. Incontinence and dribbling are common if the obstruction is urethral.

DISEASE HIGHLIGHTS

1. Clinical manifestations

   1. Upper ureteral or renal pelvic lesions can cause flank pain; lower obstruction can cause pelvic pain that sometimes radiates to the ipsilateral testicle or labium.

   2. Obstruction must be bilateral to cause AKI; therefore, the most common cause of obstructive AKI is prostatic enlargement.

   3. Urinary output

      1. Anuria, if obstruction is complete

         1. Anuria is defined as < 100 mL of urine per day.

         2. Also seen in shock, vascular lesions, severe ATN, or severe GN.

      2. Output can be normal or increased with partial obstruction.

      3. Increased output is due to tubular injury that impairs concentrating ability and sodium reabsorption.

      4. Incontinence, dribbling, decreased output, and hematuria may be present.

2. Obstruction accounts for 17% of cases of outpatient AKI, and for 2–5% of cases of inpatient AKI and is more commonly seen in men than women.

3. Obstruction can lead to a type 4 renal tubular acidosis with hyperkalemia due to tubular injury.

4. In patients with normal kidneys, unilateral obstruction often is undetected because the unobstructed kidney compensates enough to maintain normal kidney function.

5. Prognosis

   1. Complete or prolonged partial obstruction can lead to interstitial fibrosis and tubular atrophy and irreversible loss of kidney function.

      1. Complete recovery of kidney function occurs if total ureteral obstruction is relieved within 7 days; little or no recovery occurs if the total obstruction is present for 12 weeks.

      2. Obstruction is a rare cause of end-stage renal disease.

   2. Prognosis of partial obstruction is unpredictable.

EVIDENCE-BASED DIAGNOSIS

1. Urine electrolytes are not very helpful.

2. The postvoid residual will be increased (> 100 mL) if the obstruction is urethral; the postvoid residual will be normal if the obstruction is proximal to the bladder.

3. Renal ultrasound

   1. The best first test to look for obstruction

   2. Has a sensitivity of 90–98% and specificity of 65–84% for detecting urinary tract obstruction

   3. There are 4 settings in which obstruction can occur without dilatation of the complete collecting system, leading to a false-negative ultrasound.

      1. With very early (< 8 hours) obstruction

      2. When the patient is also volume depleted; sometimes repeating an ultrasound after hydration will demonstrate the dilatation

      3. With retroperitoneal fibrosis (Ormond disease), which can cause hydronephrosis without ureteral dilatation; the hydronephrosis and fibrosis are better seen on CT scan

      4. With obstruction so mild that there is no impairment in kidney function

4. Noncontrast CT can detect sites of obstruction missed on ultrasound and is superior to ultrasonography for determining the site of ureteral obstruction.

TREATMENT

1. Relieve the obstruction immediately.

   1. Modalities

      1. Indwelling urinary catheter for bladder neck obstruction

         Remember that indwelling catheters can be obstructed by clots.

      2. Suprapubic catheter, if indwelling urinary is not possible

      3. Percutaneous nephrostomy tubes for ureteral obstruction

      4. Ureteral ...