What is the most common complication of uretero-sigmoidal (ureter to sigmoid colon) anastomosis as a continent diversion in a patient with urinary bladder cancer after radical cystectomy?

Common Complications of Ureterosigmoid Anastomosis After Radical Cystectomy

The most common complication of ureterosigmoid anastomosis as a continent urinary diversion after radical cystectomy is hypokalemic, hypocalcemic, hyperchloremic, hypomagnesemic metabolic acidosis (option B).

Metabolic Complications of Ureterosigmoid Anastomosis

Ureterosigmoid anastomosis involves diverting urine into the sigmoid colon, where the anal sphincter serves as the continence mechanism for both urine and feces. While this procedure creates a continent diversion, it leads to significant metabolic derangements due to the interaction between urine and colonic mucosa:

Primary Metabolic Complication

• Hyperchloremic metabolic acidosis occurs when the colon absorbs urinary chloride in exchange for bicarbonate 1
• This is accompanied by:
  • Hypokalemia (due to increased renal potassium excretion to compensate for acidosis)
  • Hypocalcemia (acidosis mobilizes calcium from bone)
  • Hypomagnesemia (similar mechanism as calcium loss)

The severity of these electrolyte abnormalities can be profound, as demonstrated in case reports where patients developed quadriparesis and intestinal paralysis from severe hypokalemia (serum potassium as low as 1.8 mEq/L) and severe metabolic acidosis (pH 6.927) 2.

Pathophysiological Mechanism

The metabolic derangements occur through several mechanisms:

1. The colonic mucosa absorbs chloride from urine while secreting bicarbonate
2. This leads to systemic hyperchloremic metabolic acidosis
3. To compensate for acidosis:
   • The kidneys excrete more hydrogen ions and potassium, worsening hypokalemia
   • Bone buffers are mobilized, releasing calcium and causing hypocalcemia
   • Chronic acidosis stimulates osteoclastic activity, contributing to bone demineralization 1, 3

Long-term Consequences

If left untreated, these metabolic abnormalities can lead to:

• Osteomalacia/osteopenia due to chronic calcium mobilization 3
• Neuromuscular symptoms including weakness and paralysis 2
• Cardiac arrhythmias from electrolyte disturbances
• Growth retardation in children

Other Significant Complications

While metabolic complications are most common, other important complications include:

1. Neoplastic complications: Adenomas and adenocarcinomas at the ureterosigmoid anastomosis site (24% of patients at 20 years) 4
2. Infectious complications: Ascending pyelonephritis and recurrent UTIs 5
3. Surgical complications: Ureteral stricture/obstruction (reported in up to 22% of patients with urinary diversions) 1, 6

Management Recommendations

For patients with ureterosigmoid anastomosis:

1. Regular monitoring:

   • Serum electrolytes, including potassium, calcium, and magnesium
   • Blood gas analysis to detect acidosis
   • Renal function tests

2. Preventive treatment:

   • Prophylactic administration of alkalinizing agents (e.g., potassium citrate)
   • Adequate hydration
   • Dietary adjustments to minimize acidosis

3. Cancer surveillance:

   • Annual flexible sigmoidoscopy starting 10 years after surgery 4
   • Biopsies of any suspicious lesions

Clinical Pitfalls to Avoid

1. Delayed recognition of metabolic derangements - symptoms may be subtle initially
2. Inadequate monitoring - regular blood tests are essential
3. Failure to provide prophylactic alkalinizing agents - prevention is easier than treatment
4. Missing cancer surveillance - the risk of malignancy increases significantly after 10 years
5. Attributing symptoms to other causes - weakness, bone pain, or neurological symptoms should prompt evaluation for metabolic complications

Due to these significant complications, ureterosigmoid anastomosis has largely been replaced by other forms of urinary diversion, though it may still be used in select cases.