Large Bowel Obstruction

Large bowel obstruction is an interruption in the normal flow of intestinal contents through the colon and rectum. This obstruction may be mechanical (due to the actual physical occlusion of the lumen) or functional (due to a loss of normal peristalsis, also known as pseudo-obstruction). Malignancy and volvulus are the most common causes of mechanical large bowel obstruction. Typical symptoms include intermittent lower abdominal pain, abdominal distention, and obstipation. Diagnosis is established with imaging. Mechanical large bowel obstruction requires surgery in most cases.

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A large bowel obstruction (LBO) is an interruption in the normal passage of bowel contents through the colon and rectum.


  • 25% of all intestinal obstructions
  • Initial presentation of colorectal cancer (CRC) in up to 30% of cases
  • Average age of presentation due to a malignant cause is 73 years.
  • The average delay in seeking medical help is 5 days.
  • Functional obstruction (pseudo-obstruction) is more common in: 
    • Men
    • Age > 60 years


  • Mechanical:
    • Colorectal cancer: most common cause
    • Metastatic cancers (ovarian, pancreatic, lymphoma)
    • Volvulus (sigmoid and cecal): most common benign cause
    • Strictures from: 
      • Prior colon resection (up to 30% of surgeries with colorectal anastomosis)
      • Inflammatory disease (diverticulitis, ischemic colitis, inflammatory bowel disease)
    • Post-surgical adhesions 
    • Hernias 
    • Rare causes:
      • Radiotherapy
      • Suppository use
      • Tuberculosis
      • Endometriosis
      • Intussusception
      • Lymphogranuloma venereum (Chlamydia trachomatis)
  • Functional (pseudo-obstruction, also known as Ogilvie’s syndrome):
    • Severe systemic illness
    • Surgery (most commonly from cesarean section or hip surgery)
    • Trauma
    • Spinal anesthesia
    • Medications (opiates, anticholinergics, calcium channel blockers)



  • Bowel dilation results from accumulation of:
    • Swallowed air and intestinal secretions proximal to the obstruction
    • Gas from bacterial fermentation
  • ↑ intraluminal pressure → compression of intramural vessels → intestinal ischemia → colon necrosis and/or perforation
  • Open-loop LBO (10%–20%):
    • Incompetent ileocecal valve allows reflux of contents into the ileum.
    • Some intraluminal pressure in the colon is relieved.
    • Can present similar to small bowel obstruction (vomiting, abdominal cramping)
  • Closed-loop LBO (80%–90%): 
    • Competent ileocecal valve or volvulus 
    • Results in proximal and distal occlusion
    • ↑ Risk of ischemia or perforation
Pathophysiology of large bowel obstruction

Pathophysiology of LBO

Image by Lecturio.

Pathophysiology for specific etiologies

  • Mechanical:
    • Malignancy:
      • 70% at, or distal to, the transverse colon
      • Progressive, gradual distention of the proximal segments 
      • Perforation is a common complication, likely from inflammation or tumor invasion.
    • Volvulus:
      • Torsion of a colonic segment → obstruction of the colonic lumen
      • Can result in vascular perfusion impairment
      • If untreated → ischemia and perforation
    • Strictures: can result from recurrent inflammation (diverticulitis, Crohn’s disease)
  • Functional obstruction (pseudo-obstruction):
    • Exact mechanism is unknown.
    • Impairment of parasympathetic fibers S2–S4 has been implicated.
    • Progressive distention ↑ tension on the colonic wall
    • ↑ Risk of ischemia and perforation:
      • Cecal diameter > 10–12 cm (3.9–4.7 in)
      • Distention present for > 6 days

Clinical Presentation

Acute obstruction symptoms

  • Common for volvulus, hernias, and pseudo-obstruction
  • Abdominal pain
    • Usually below the umbilicus
    • Cramping with paroxysms (every 20–30 min)
    • Constant focal pain: may indicate ischemia or necrosis
    • Diffuse peritonitis suggests perforation.
  • Abdominal bloating and distension
  • Nausea and vomiting more common with proximal (right colon) or open-loop obstruction
  • Constipation or obstipation (unable to pass stool or flatus)

Chronic obstruction syndrome

  • Common for CRC
  • Gradual change in bowel habits (weeks to months):
    • Progressively worsening constipation
    • Increased straining with defecation
    • Change in stool caliber (“pencil-like” stools)
  • Weight loss 
  • Melena or rectal bleeding
  • Tenesmus (pain with defecation) suggests a rectal tumor.
  • Constitutional symptoms suggestive of cancer:
    • Weight loss
    • Fatigue
    • Unexplained fevers, chills, or night sweats

Physical exam

  • General:
    • Signs of malnutrition (emaciated, loss of body fat)
    • Dehydration (dry mucous membranes, loss of skin turgor)
  • Abdominal:
    • Distention can be pronounced in:
      • Complete distal obstructions
      • Pseudo-obstruction
      • Sigmoid volvulus
    • Tympanic to percussion
    • Tenderness:
      • Focal: local peritoneal irritation from inflammation or ischemia
      • Diffuse: suggests generalized peritonitis (concern for perforation)
    • Mass:
      • Palpable tumor in thin patients
      • Cecal volvulus 
  • Digital rectal exam:
    • Low rectal tumors can be palpable.
    • Blood (gross or occult) is concerning for cancer.


Relevant history

  • Change in bowel habits
  • Timing and findings of last colonoscopy
  • History of other malignancies (e.g., ovarian, lymphomas, other gastrointestinal tumors)
  • Family history of colorectal cancer

Laboratory studies

  • Complete blood count (CBC):
    • ↓ Hemoglobin: cancer or chronic disease
    • ↑ Hemoglobin and hematocrit (hemoconcentration): dehydration
    • Leukocytosis may suggest:
      • Complications: perforation, ischemia
      • Underlying cause: inflammation, infection
  • Chemistry:
    • Dehydration and electrolyte loss:
      • ↓ Potassium
      • ↓ Sodium
      • ↓ Magnesium
      • ↑ Blood urea nitrogen (BUN)/creatinine ratio
      • Metabolic alkalosis (early) or acidosis (late stage, suggests ischemia)
    • ↑ Lactate suggests ischemia or sepsis
    • ↓ Albumin suggests malnutrition
  • Tumor markers:
    • Carcinoembryonic antigen (CEA): strongly suggestive of CRC
    • Cancer antigen (CA) 19-9: if primary ovarian cancer is suspected


  • Upright abdominal and chest X-ray:
    • Colonic distention (> 6 cm (2.4 in); cecum > 9 cm (3.5 in))
    • Collapsed distal colon
    • Volvulus:
      • A distended loop of colon (sigmoid or cecum)
      • “Northern exposure” sign: sigmoid loop ascending toward transverse colon
      • “Coffee bean” sign: distended sigmoid loop pointing toward right upper quadrant 
    • Pneumoperitoneum (air under diaphragm) if perforation has occurred
    • Pseudo-obstruction: 
      • Colonic distention from the cecum to splenic flexure or rectum
      • Cecum diameter > 10–12 cm (3.9–4.7 in) is worrisome for impending perforation.
  • Computed tomography (CT) scan:
    • Differentiates between mechanical and pseudo-obstruction
    • May help determine causes of obstruction
    • Can distinguish between sigmoid and cecal volvulus
    • Perforation: pneumoperitoneum
    • Ischemia:
      • Thickening of the bowel wall
      • Pneumatosis coli (air in the colon wall)
      • Portal venous gas
    • Volvulus findings:
      • “X marks the spot” sign: 2 crossing transition points
      • “Split-wall” sign: separation of the sigmoid wall by mesenteric fat
      • “Whirl” sign: swirling of the mesentery
      • “Beak” sign: tapering of the colon to the point of obstruction
    • CRC findings:
      • Transition point with proximal dilation
      • Intrinsic mass (sometimes appears as an “apple core” lesion)
      • Will show synchronous and metastatic lesions if present
    • Pseudo-obstruction:
      • Diffuse dilation without obvious obstruction cause
      • May have an intermediate transition zone at the splenic flexure
  • Contrast enema:
    • Should not be used in patients with peritonitis or a high suspicion of perforation or ischemia
    • Will show colon dilation
    • “Apple core” lesion may be present in CRC

Colonoscopy or sigmoidoscopy

  • Can be used to confirm a diagnosis of CRC and obtain tissue biopsy
  • Can also allow decompression:
    • Sigmoid volvulus
    • Pseudo-obstruction


Initial supportive management

  • Intravenous (IV) resuscitation
    • Hydration
    • Electrolyte correction
  • Bowel rest: NPO (nothing by mouth) or clear liquids
  • Nasogastric decompression if vomiting or significant small bowel dilation
  • Empiric antibiotics if ischemia or perforation is suspected
    • Piperacillin-tazobactam
    • Ciprofloxacin or a 3rd-generation cephalosporin, plus metronidazole: Ampicillin or vancomycin may be added for enterococcal coverage in severe disease.
    • Carbapenems for severe disease

Mechanical obstruction

  • Endoscopic treatments:
    • Decompressive sigmoidoscopy for volvulus:
      • Reduces (untwists) volvulus
      • Allows a delayed (elective), rather than emergent, sigmoid colon resection
      • If subsequent surgery is not performed, 50% will recur.
      • For high-risk patients who cannot tolerate surgery, this may be the only intervention.
      • Not an effective option for cecal volvulus
    • Endoscopic stenting for malignant obstruction:
      • A less invasive alternative to diverting colostomy
      • Palliative option for patients with unresectable CRC or metastatic disease
      • Bridge to radiation, chemotherapy, and definitive resection
  • Surgery:
    • 75% of mechanical LBOs will require surgery.
    • 1-stage procedure:
      • Resection of the affected colon segment with primary anastomosis
      • Preferred
      • Indicated for stable patients
    • 2-stage procedure:
      • Resection of affected colon with end colostomy or diverting loop ileostomy
      • Followed by an ostomy reversal in 3–6 months, or when medically feasible
      • Indicated for those with a high risk of anastomotic leak and mortality
    • 3-stage procedure:
      • Diverting colostomy or ileostomy
      • Followed by subsequent colon resection
      • Eventual ostomy reversal with primary anastomosis when feasible
      • Indicated for unstable, frail patients with multiple comorbidities, or those who will need chemotherapy or radiation prior to definitive resection
    • Other procedures for less common causes:
      • Hernia repair
      • Lysis of adhesions
      • Revision of prior anastomosis (for anastomotic strictures)
Operative findings showing large sigmoid volvulus

Operative findings showing a large sigmoid volvulus

Image: “F2” by General Surgery Department, Aga Khan University Hospital, Stadium Road, Karachi 74800, Pakistan. License: CC BY 2.0

Pseudo-obstruction (Ogilvie’s syndrome)

  • Initial management (for stable patients without peritonitis in 1st 48–72 hours and a cecal diameter < 12 cm (4.7 in)):
    • Supportive
    • Rectal tube for decompression
    • Stop offending medications (opiates, anticholinergics, calcium channel blockers).
    • Treat underlying illness.
    • Follow with serial physical exams and X-rays every 12–24 hours.
  • Pharmacologic interventions:
    • Indications:
      • No improvement in 72 hours
      • Cecal diameter > 12 cm (4.7 in)
    • IV neostigmine (acetylcholinesterase inhibitor):
      • Bolus dosing or continuous infusion
      • 89% respond to a single dose
      • Patients need to be in the monitored setting.
    • Methylnaltrexone: if the obstruction is precipitated by opiates
  • Colonoscopic decompression:
    • Indications:
      • No response to neostigmine
      • Contraindications to neostigmine
    • Has a 3% perforation rate
  • Surgery:
    • Indications: 
      • Failure of non-surgical management
      • Peritonitis (ischemia or perforation)
    • Primary anastomosis (stable patients)
    • Total abdominal colectomy with end ileostomy (ischemia or perforation)

Differential Diagnosis

  • Toxic megacolon: a complication of severe colitis, frequently associated with C. difficile, inflammatory bowel disease, or ischemic colitis. Patients present with severe abdominal distention and pain with associated systemic toxicity (fever, tachycardia, and altered mental status). The diagnosis is established with the history, physical findings, and imaging (CT scan). Treatment depends on the cause, but can include supportive care and surgery.
  • Small bowel obstruction: an interruption of intraluminal contents through the small bowel due to a mechanical or functional problem. Patients present with abdominal pain, distention, nausea, and vomiting. Imaging will show involvement of the small bowel, although both the colon and small bowel may be distended in functional obstruction. Most cases will resolve with supportive care.
  • Diverticulitis: inflammation of the colonic diverticula. Patients present with crampy, lower abdominal pain, and may have constipation. Diverticulitis frequently is also associated with fever and leukocytosis. A CT scan shows the characteristic findings. Treatment includes bowel rest, antibiotics, and occasionally surgery.
  • Appendicitis: inflammation of the appendix. Early appendicitis can present with diffuse colicky pain, but pain and tenderness eventually localize to the right lower quadrant. Diagnosis is established by a CT scan. Treatment includes antibiotics and surgery.
  • Chronic megacolon: dilation of the colon, which can be congenital (Hirschsprung’s disease) or due to systemic disease (e.g., neurologic or autoimmune disease). Patients will have a distended, tympanic abdomen. The history and imaging are used for the diagnosis. Management includes treating any underlying cause, a strict bowel regimen, decompression, and potential surgery.


  1. Camilleri M. (2020). Acute colonic pseudo-obstruction (Ogilvie’s syndrome). In Grover, S. (Ed.), UpToDate. Retrieved December 9, 2020, from
  2. Yeh D.D, Bordeianou L. (2019). Overview of mechanical colorectal obstruction. In Chen, W. (Ed.), UpToDate. Retrieved December 8, 2020, from
  3. Niknejad, M.T., Jones J. et al. (2015). Large Bowel Obstruction. Retrieved December 9, 2020, from
  4. Ansari, P. (2020). Intestinal obstruction. [online] MSD Manual Professional Version. Retrieved December 10, 2020,
  5. Hopkins, C. (2017). Large-bowel obstruction. In Dronen, S.C. (Ed.), Medscape. Retrieved December 10, 2020, from

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