What is the significance and management of a dilated sigmoid colon?

Significance and Management of Dilated Sigmoid Colon

A dilated sigmoid colon is a serious clinical finding that most commonly indicates sigmoid volvulus, which requires prompt intervention to prevent significant morbidity and mortality. 1

Clinical Significance

• Sigmoid volvulus is a major cause of large bowel obstruction, accounting for 10-15% of all cases in the United States 2
• Dilated sigmoid colon (>6.5 cm measured at the pelvic brim) can indicate several serious conditions including:
  • Sigmoid volvulus (twisting of the sigmoid colon on its mesenteric axis) 1, 3
  • Acute colonic pseudo-obstruction (Ogilvie's syndrome) 4
  • Toxic megacolon (secondary to inflammatory bowel disease or infectious colitis) 5, 6
  • Chronic megacolon (congenital or acquired) 5

Clinical Presentation

• Classic triad of sigmoid volvulus: abdominal pain, constipation, and abdominal distension 3
• Physical examination typically reveals pronounced and asymmetric abdominal distension with diminished bowel sounds 3
• Empty rectum on digital examination is characteristic 3
• Warning signs of complications include peritoneal signs, shock, or renal insufficiency 3

Diagnostic Approach

• Plain abdominal radiographs are first-line, looking for the "coffee bean sign" 1
• Abdominal CT is the gold standard, showing dilated colon with the "whirl sign" representing twisted colon and mesentery 1
• Rule out mechanical obstruction at the rectosigmoid junction through endoscopy or virtual colonography 7

Management Algorithm

For Sigmoid Volvulus:

1. Immediate surgical intervention is mandatory for patients with:

   • Septic shock
   • Evidence of bowel ischemia
   • Perforation 1

2. For uncomplicated sigmoid volvulus:

   • First-line treatment is endoscopic decompression (success rate 70-91%) 1
   • After successful decompression, definitive sigmoid resection should be performed during the same hospital admission to prevent recurrence 1, 7
   • Without resection, recurrence rates are extremely high (45-71%) 7, 1, 3

3. If endoscopic decompression fails:

   • Urgent sigmoid resection is indicated 7
   • Surgical options include:
     • Sigmoid resection with end colostomy (Hartmann procedure)
     • Sigmoid resection with primary anastomosis (with or without diverting ostomy) 7

For Other Causes of Dilated Sigmoid:

• Acute colonic pseudo-obstruction:

  • Supportive care, discontinue contributing medications, correct metabolic disturbances
  • Neostigmine for cases unresponsive to conservative measures
  • Endoscopic decompression if neostigmine fails or is contraindicated
  • Surgery if signs of perforation develop 4

• Toxic megacolon:

  • Treat underlying inflammatory or infectious cause
  • Bowel rest and close monitoring
  • Emergency colectomy may be needed if perforation occurs 5, 6

• Chronic megacolon:

  • Treatment depends on etiology (surgical for Hirschsprung's disease, biofeedback for pelvic floor dysfunction)
  • Medical management with enemas, fiber, and laxatives for chronic idiopathic megacolon 5

Critical Considerations

• Risk of colonic perforation increases when cecal diameter exceeds 12 cm and distention has been present for >6 days 4
• Mortality is significantly higher with emergency surgery (12-20%) compared to elective surgery (5.9%) 1
• Risk factors for increased mortality include age over 60 years, presence of shock on admission, and history of previous volvulus episodes 1
• Laparoscopic approach may be suitable in select cases but benefits in emergency settings remain unclear 1

Pediatric Considerations

• Sigmoid volvulus is rare in children but can occur due to Hirschsprung's disease, congenital anomalous fixation of the colon, or chronic constipation 8
• Prompt diagnosis and treatment are essential to prevent gangrene, perforation, and septic shock 8