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Bowel Obstruction — Comprehensive Overview

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Definition

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Classification

By Mechanism

By Location of Obstructing Lesion (relative to bowel wall)

• Extrinsic — adhesions, hernias, peritoneal neoplasms
• Intrinsic (intramural) — primary neoplasms, Crohn's stricture, hematoma, radiation damage
• Intraluminal — bezoars, foreign bodies, gallstone ileus, fecal impaction

By Loop Dynamics

• Simple obstruction — obstruction at a single point; proximal decompression is possible
• Closed-loop obstruction — obstruction at two sites; no proximal escape; rapidly leads to ischemia and necrosis; mortality is twice that of simple SBO

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Small Bowel Obstruction (SBO)

Epidemiology

• Accounts for the majority of all bowel obstructions
• Responsible for ~2% of all ED visits for abdominal pain
• Approximately 300,000 hospitalizations/year in the U.S.
• Mortality has fallen from ~60% (1900) to <8% with modern management

Causes (in order of frequency)

• Gallstone ileus: Rare (1–4% of SBO); gallstone enters bowel via cholecystoduodenal fistula, migrates distally, lodges at the ileum (narrowest segment). Most common in elderly patients.
• Small bowel volvulus: Rare in the West (3–6%); commoner in Africa/India/Middle East (up to 20%). Closed-loop → strangulation risk is high. Surgical emergency.
• Intussusception: Most common cause of obstruction in children 6–36 months. In adults, a mechanical cause (often tumor) is found in >90% of cases.
• Obturator hernia: Rare; older, thin women; no external mass → diagnosis frequently delayed; highest mortality (~70%) of any abdominal hernia when incarcerated.

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Large Bowel Obstruction (LBO)

Epidemiology

• 4–5× less common than SBO in Western countries
• Affects an older population
• Patients present for medical attention on average 5 days after symptom onset (better tolerated than SBO due to slower distention)

Causes (~90% from 3 entities)

1. Colorectal adenocarcinoma — most common cause in the USA; ~30% of CRC patients present obstructed; left-sided (distal to splenic flexure) tumors predominate because lumen is narrower and stool is more solid
2. Colonic volvulus — 5–10% of LBO; sigmoid (75%) > cecal (22%); volvulus is the leading cause in developing countries
3. Diverticular disease — fibrotic intramural stricture

Pathophysiology of LBO — Ileocecal Valve (ICV) Competence

• Competent ICV (75% of patients): colonic contents cannot decompress into small bowel → closed-loop obstruction → rapid ischemia and perforation risk
• By the Law of LaPlace: wall tension = intraluminal pressure × radius. The cecum (widest, thinnest wall) is most vulnerable to ischemia and rupture
• Critical cecal diameter: 10–13 cm (perforation risk is significant)
• Cecal dilation >12–14 cm on plain film = surgical emergency
• Incompetent ICV: contents back up into small bowel → massive distension, feculent emesis over weeks to months

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Pathophysiology (General)

1. Obstruction → intraluminal accumulation of GI secretions (gastric, biliary, pancreatic) continues even without oral intake
2. Distention → increased intraluminal pressure → enhanced peristaltic contractions, air swallowing
3. Vomiting + reduced intake + decreased absorption → volume depletion, hemoconcentration, electrolyte imbalance, renal failure, shock
4. When intraluminal pressure exceeds capillary/venous pressure → bowel wall ischemia, decreased lymphatic drainage
5. Bacterial overgrowth, translocation → septicemia and bowel necrosis
6. This cascade accelerates in closed-loop obstruction

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Clinical Features

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Diagnosis

Plain Abdominal X-Ray

• SBO: dilated small bowel loops with air-fluid levels on upright film; "stepladder" pattern; absence of colonic gas
• LBO: dilated colon peripheral/frame-like; cecal distention
• Combination of upright + supine films: excellent sensitivity for LBO but lower specificity (cannot reliably distinguish from ileus/pseudo-obstruction)
• Colonic loop ≥6 cm or cecal diameter ≥9 cm = dilated

CT Scan (imaging of choice)

• Identifies transition point, cause, and complications (ischemia, perforation)
• Malignant obstruction features: mass at obstruction site, adenopathy, abrupt transition zone with irregular bowel thickening
• Benign obstruction features: mesenteric vascular changes, large ascites, smooth transition zone, smooth bowel thickening
• CT enteroclysis: water-soluble contrast via naso-enteric tube followed by CT — useful for challenging low-grade SBO
• Signs of impending perforation: cecal dilation >10 cm, pneumatosis intestinalis, portal venous gas, pneumoperitoneum

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Management

Initial Stabilization (all bowel obstruction)

• IV fluid resuscitation + electrolyte replacement
• Nasogastric (NG) decompression — relieves distension; may allow non-surgical resolution (especially adhesive SBO)
• NPO (bowel rest)
• Foley catheter for urine output monitoring
• Correct underlying metabolic abnormalities

SBO Management

• Indicated for adhesive SBO (most common cause) — majority resolve without surgery
• Bowel rest, IV fluids, NG decompression, pain control
• Water-soluble contrast agents (e.g., Gastrografin) have both diagnostic and therapeutic roles — promote resolution and predict need for surgery

• Indicated for: failed conservative management, suspected/confirmed strangulation, peritonitis, closed-loop obstruction, incarcerated/strangulated hernia, complete obstruction not responding to non-operative treatment
• Options: lysis of adhesions, bowel resection with/without anastomosis, hernia repair, enterostomy

LBO Management

• Resection + anastomosis with diverting ileostomy
• Resection + end colostomy (Hartmann's procedure)
• Diverting proximal colostomy alone (without resection)
• Endoscopic stenting — bridge to surgery (decompression + bowel prep → elective single-stage resection) OR palliative (in advanced disease)
  • Risk of perforation, occlusion, migration; requires experienced endoscopist

Malignant Bowel Obstruction (palliative)

• Opioids for abdominal pain
• Antiemetics (dopamine antagonists: phenothiazines, butyrophenones) for nausea
• Antisecretory agents (anticholinergics, octreotide) — reduce colicky pain and intestinal secretions
• Glucocorticoids — anti-inflammatory; may assist resolution
• Metoclopramide — cautiously for incomplete/functional obstruction only; contraindicated in complete obstruction
• NG tube relief or venting gastrostomy for prolonged palliation

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Special Entities

Strangulated Bowel Obstruction

• Compromise of bowel blood supply → ischemia → necrosis → perforation
• Clinical: fever, tachycardia, severe unrelenting pain, peritonism, leukocytosis
• Mortality doubles compared to simple obstruction
• Surgical emergency

Intussusception

• Telescoping of a bowel segment into the distal segment
• Children <2 years: usually idiopathic (often linked to Peyer patch hyperplasia, adenovirus); treated with contrast enema reduction
• Adults: >90% have a mechanical lead point (tumor in >65%); requires surgery
• Complications: obstruction, mesenteric vessel compression, infarction

Hirschsprung Disease

• Congenital aganglionic megacolon (1:5000 live births); males > females
• Failure to pass meconium in neonatal period → obstructive constipation
• Complications: enterocolitis, perforation, electrolyte disturbances
• Treatment: surgical resection of aganglionic segment + anastomosis

Adynamic Ileus vs. Mechanical Obstruction

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Key Numbers to Remember

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