Large Bowel Obstruction

Large bowel obstruction occurs when there is a bowel obstruction distal to the ileocecal valve. Bowel obstructions have been documented as early as 1550 B.C. in the Papyrus.

Etiology

• Mechanical obstruction (dynamic)
  • Colorectal cancer is the most common cause in the U.S.
  • Endoluminal causes
    • Intrinsic mass
    • Foreign body
    • Bezoar
    • Fecal impaction
  • Mural causes
    • Diverticular stricture
    • Crohn disease stricture
    • Ischemic stricture
    • Radiation stricture
    • Infectious
    • Hirschsprung disease
  • Extraluminal causes
    • Sigmoid volvulus
    • Cecal volvulus
    • Hernia (i.e., inguinal, ventral, internal)
    • Metastatic/intraabdominal tumor
    • Abdominal abscess
    • Retroperitoneal fibrosis
    • Adhesions 
• Functional obstruction (adynamic)
  • Colonic pseudo-obstruction (Ogilvie)
  • Toxic megacolon
  • Paralytic ileus

History and Physical Exam

• Mechanical versus functional obstruction
  • Mechanical obstruction
    • Increased peristalsis
    • Low-grade colicky pain
  • Functional obstruction
    • Abdominal distention
    • Vague abdominal pain
• Acute versus chronic obstruction
  • Acute obstruction
    • Rapid onset of pain
    • Abdominal distention
    • Abdominal tenderness 
  • Chronic obstruction
    • Obstipation
    • Abdominal distention
    • Pencil-thin stools
    • Intermittent abdominal pain

Imaging

• Abdominal X-ray (location)
• Water-soluble and IV contrast-enhanced CT (location, etiology)
• Flexible endoscopy (diagnosis, biopsy)

Treatment

• Depends on etiology
• Surgery → for peritonitis, signs of perforation, ischemic bowel, patients that fail decompression for sigmoid volvulus, cecal volvulus, hernias, intussusception, cancer
• Endoscopic decompression (using rigid or flexible sigmoidoscope) → for sigmoid volvulus
• Steroids → for obstruction and active IBD
• Drainage → for paracolic abscesses
• Endoscopic removal → for foreign body removal
• Stool softeners, laxatives, and manual disimpaction → for fecal impaction

Relevant Information

• Volvulus is responsible for ⅓ of cases
  • Most common site is sigmoid colon
  • Cecal volvulus can also occur 
  • Can occur at any portion of the colon not fixed to the retroperitoneum with elongated mesentery
• Closed-loop obstruction
  • Occurs when proximal and distal parts of bowel are obstructed; colon becomes progressively distended with pressure increasing to the point of ischemic necrosis and perforation
  • Potential for rapid deterioration with ischemia and bowel perforation
  • Commonly encountered in cases of volvulus and strangulated hernias and in cases of obstructing colon cancers
• Pneumatosis intestinalis: air on the bowel wall; associated with ischemia and dissection of air through areas of the bowel wall
• Air in the portal system usually indicates significant infection or necrosis of the large or small bowel; often an ominous sign

• Large bowel = colon + rectum; 150 cm in length (roughly 5 feet)
• Covered with peritoneum; no mesentery
• Cecum
  • Most common location for necrosis and perforation as it has the largest diameter
  • Distends more under lower pressures and develops higher wall stress, per law of Laplace
  • Law of Laplace: tension = pressure x diameter
  • Risk of ischemic necrosis and perforation increases with diameter > 12 cm
  • Ileocecal valve
    • Where terminal ileum empties into cecum
    • Thickened, nipple-shaped invagination containing circular muscle
  • Appendix
    • Extends from cecum 3 cm below ileocecal valve
    • Blind-ending elongated tube 8 – 10 cm in length
• Ascending colon
  • Begins at ileocecal junction and continues to hepatic flexure
  • 15 cm in length (0.5 feet)
  • Covered with peritoneum anteriorly and laterally 
  • Fixed against retroperitoneum by fascia of Toldt posteriorly
  • Best mobilized along lateral peritoneal reflection by incising “white line of Toldt”
• Transverse colon
  • 45 cm in length (roughly 1.5 feet)
  • Covered by visceral peritoneum
  • Greater omentum is attached at superior aspect; lifting upward with downward traction will reveal an avascular plane adjacent to the colon (most easily identified close to midline)
• Descending colon
  • Begins at splenic flexure (where intestine loses its mesentery) to the sigmoid colon
    • Splenic flexure
      • Where transverse colon is flexed downward
      • Suspended by four mainly avascular ligaments
        • Phrenicocolic ligament
        • Splenocolic ligament
        • Renocolic ligament
        • Pancreaticocolic ligament
    • Sigmoid colon
      • Begins at or below level of iliac crest where colon becomes completely intraperitoneal again
      • Thicker and more mobile compared to descending colon
      • When mobilizing, the mesenteric fold is the surgical landmark for underlying left ureter
      • Ends at rectosigmoid junction (where colonic taenia confluence for form complete longitudinal muscle layer, and colon loses its mesentery)
  • 25 cm in length (0.82 feet)
  • Commonly dissected along the line of Toldt from below and then enter lesser sac by lifting omentum above transverse colon
    • Lesser sac (lesser peritoneal sac, omental bursa)
      • Potential space that exists within the abdomen between the stomach and the pancreas
      • Formed by greater and lesser omentum
  • Smaller in diameter than ascending colon
• Meandering mesenteric artery (arc of Riolan, Moskowitz artery)
  • Thick collateral vessel that courses closely to the base of the mesentery
  • Connects SMA or middle colic artery to the IMA or left colic artery
  • Presence suggests occlusion of one of the major mesenteric arteries

Complications

• Perforation
• Bowel necrosis, ischemia, gangrene
• Sepsis
• Electrolyte alterations
• Dehydration
• Death

Differential Diagnoses

• Megacolon
• Diverticulitis
• Small bowel obstruction
• Abdominal hernia