Bowel Obstruction: SBO and LBO Diagnosis & Management
Bowel obstruction — mechanical blockage of the intestinal lumen — is divided into small bowel obstruction (SBO, 75% of cases, most commonly adhesions) and large bowel obstruction (LBO, 25%, most commonly colorectal cancer). Correct classification guides management: partial SBO can be managed non-operatively, but strangulation or complete obstruction requires urgent surgery.
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Progress Note Editorial · Evidence-based
Updated July 2026
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The 60-second version
SBO: adhesions most common cause (60–70%); LBO: colorectal cancer most common cause (60%)
CT abdomen/pelvis is gold standard; strangulation signs (pneumatosis, portal venous gas) = emergency surgery
Partial SBO: trial of NPO + NG tube decompression for 48–72h; gastrografin challenge is both diagnostic and therapeutic
Sigmoid volvulus: coffee bean sign on X-ray; treat with flexible sigmoidoscopy; cecal volvulus requires surgery
Closed-loop obstruction = highest ischemia risk; virgin abdomen with SBO = less likely adhesive, more likely to need surgery
Small Bowel Obstruction (SBO): Causes, Presentation, Imaging
**Most common causes (mnemonic AHHH)**: **A**dhesions (most common in adults, 60–70% — prior abdominal surgery), **H**ernia (inguinal, femoral, incisional — most common in patients with no prior surgery), **H**intussusception (most common in children <2, lead point in adults = malignancy/Meckel's), **H**arlington's tumor (neoplasm). Also: volvulus, Crohn's disease stricture, gallstone ileus (air in biliary tree on X-ray = Rigler's triad). **Presentation**: colicky periumbilical pain, nausea/vomiting (bilious early; feculent late = more distal), distension, obstipation (no flatus = complete). **X-ray**: dilated small bowel loops (>3 cm, central distribution, valvulae conniventes = complete plicae), air-fluid levels, paucity of colonic gas. **CT abdomen/pelvis with IV contrast** (gold standard): transition point, dilated proximal and decompressed distal bowel. Signs of strangulation (ischemia): free fluid, pneumatosis intestinalis, portal venous gas, mesenteric edema, decreased bowel wall enhancement — these mandate emergency surgery.
Large Bowel Obstruction (LBO): Causes and Volvulus
**Most common causes**: colorectal carcinoma (most common, 60%), volvulus (20%, most commonly sigmoid colon), diverticular stricture, Ogilvie syndrome (colonic pseudo-obstruction — no mechanical obstruction). **Sigmoid volvulus**: elderly, institutionalized, chronic constipation; X-ray shows 'coffee bean' sign (massively dilated sigmoid loops pointing to right upper quadrant); initial treatment = flexible sigmoidoscopy decompression (if no peritonitis) followed by elective sigmoid resection. **Cecal volvulus**: younger patients, CT with 'whirl sign'; requires surgery (right hemicolectomy) — endoscopic decompression unreliable. **Colorectal cancer obstruction**: CT identifies tumor + level; emergent surgical options: Hartmann procedure (sigmoid colectomy + colostomy — safest for unprepared bowel), or self-expanding metal stent as bridge to elective surgery (controversial). **Ogilvie syndrome**: IV neostigmine (anticholinesterase) is first-line after colonoscopic decompression failure; occurs in ICU/post-operative patients.
Management Principles: Operative vs Non-operative
**Initial management (all obstructions)**: NPO (nil per os), nasogastric tube (NG tube) for decompression and symptom relief, IV fluids (LR preferred) for resuscitation, serial abdominal exams, Foley catheter for urine output monitoring, correct electrolytes (hypokalemic hypochloremic metabolic alkalosis from vomiting). **Non-operative (partial SBO)**: 80% resolve with conservative management; trial for 48–72h; gastrografin challenge (water-soluble contrast study) both diagnostic and therapeutic for adhesive SBO. **Operative indications**: complete SBO not resolving after 48–72h, any signs of strangulation (ischemia), peritonitis, free air on imaging, virgin abdomen (no prior surgery — less likely adhesive), closed-loop obstruction (two points of obstruction → highest ischemia risk), volvulus not decompressible endoscopically, LBO from malignancy. **Post-operative care**: risk of short bowel syndrome if significant bowel resection, TPN if >100 cm small bowel removed.
Test yourself
Quick check — 3 questions
1. A 72-year-old man with no prior abdominal surgery presents with 3 days of colicky abdominal pain, abdominal distension, and obstipation. KUB shows massively dilated sigmoid colon loops forming a 'coffee bean' shape pointing to the right upper quadrant. What is the diagnosis and appropriate next step?
Explanation. Coffee bean sign pointing to the RUQ on plain film = sigmoid volvulus (the sigmoid twists on its mesentery and distends massively). In the absence of peritonitis or ischemia, flexible sigmoidoscopy is used for decompression (successful in 75–95% of cases). After decompression, elective sigmoid resection is performed during same hospitalization to prevent high recurrence rate (90%). Cecal volvulus would show the cecum (not sigmoid) displaced, and requires surgery.
2. A 55-year-old woman with prior hysterectomy presents with nausea, vomiting, and periumbilical pain for 24 hours. CT shows dilated small bowel loops to 4 cm with a transition point in the right lower quadrant, decompressed distal bowel, and no free fluid or pneumatosis. What is the appropriate initial management?
Explanation. This is a partial SBO (dilated bowel with transition point, but no ischemia signs on CT). Prior hysterectomy → adhesions are the likely cause. Initial management: NPO, NG tube decompression, IV fluids. Gastrografin (water-soluble contrast) challenge: diagnostic (confirms resolution or non-resolution) and therapeutic (osmotic action draws fluid into bowel lumen, may help resolve adhesive SBO). No ischemia signs = not emergently operative. 80% of partial adhesive SBO resolve non-operatively.
3. A 68-year-old man presents with large bowel obstruction on CT. The obstructing mass is at the sigmoid colon with a surrounding soft tissue mass — biopsy confirms adenocarcinoma. He is hemodynamically stable with no peritonitis. Which operative approach is most appropriate for emergency decompression?
Explanation. Hartmann procedure is the safest approach for emergent LBO from sigmoid colorectal cancer: resect the sigmoid + obstructing tumor, create end colostomy, oversew the rectal stump. Primary anastomosis on unprepared bowel carries high anastomotic leak risk. Diverting loop colostomy alone leaves the tumor in place. Colonic stent as bridge to elective surgery is an option in selected patients but remains controversial and not universally recommended due to stent migration/perforation risk. Hartmann is the most reliable emergency option.
Frequently asked questions
What are the signs of strangulation in bowel obstruction and why do they mandate surgery?
Strangulation (bowel ischemia) signs: fever, constant (not colicky) severe pain, peritoneal signs (rebound, guarding), leukocytosis with bandemia, lactic acidosis, CT findings of pneumatosis intestinalis (air in bowel wall), portal venous gas, decreased bowel wall enhancement, free fluid. Strangulation = compromised blood supply → bowel infarction, perforation, sepsis, death within hours. It cannot be managed non-operatively — immediate surgery is required.
Why is a 'virgin abdomen' (no prior surgery) important in evaluating SBO?
Adhesions (the most common SBO cause) only form after prior abdominal surgery or peritoneal inflammation. A patient with no prior surgery presenting with SBO is less likely to have adhesive disease and more likely to have a hernia, malignancy, volvulus, or Crohn's as the etiology. These causes are less responsive to conservative management, so a lower threshold for earlier surgical intervention is appropriate in virgin abdomen SBO.
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