Acute Abdominal Emergencies — Part 3: Small Bowel Obstruction, Large Bowel Obstruction & Diverticulitis

6. Small Bowel Obstruction

6.1 Epidemiology and Etiology

Small bowel obstruction (SBO) accounts for approximately 15% of all emergency department visits for abdominal pain and is responsible for approximately 300,000 hospitalizations annually in the United States. SBO is the most common indication for emergency abdominal surgery.^{1 2}

Etiology by Frequency:

6.2 Diagnosis

Clinical Presentation

The classic presentation includes:

• Colicky abdominal pain — intermittent, cramping, periumbilical
• Nausea and vomiting — earlier and more profuse with proximal (jejunal) obstruction; may be bilious or feculent (late finding)
• Abdominal distension — more prominent with distal (ileal) obstruction
• Obstipation — inability to pass flatus or stool (complete obstruction); some patients with partial SBO may continue to pass flatus

Physical Examination:

• Distension (may be absent in proximal/high obstruction)
• High-pitched, hyperactive bowel sounds (early); absent bowel sounds (late)
• Localized tenderness may indicate strangulation
• Examine ALL hernial orifices — groin (inguinal, femoral), umbilical, incisional sites
• Peritoneal signs (guarding, rebound, rigidity) suggest strangulation or perforation

CT Abdomen/Pelvis with IV Contrast

CT is the imaging modality of choice for suspected SBO and should be obtained in virtually all patients with suspected bowel obstruction.^{1 2}

Key CT Findings:

Plain Radiographs

Plain abdominal radiographs have limited sensitivity (approximately 50–70%) and are largely superseded by CT. When obtained:

• Dilated small bowel loops (>3 cm) with air-fluid levels on upright film
• “String of pearls” sign — small pockets of air trapped between valvulae conniventes in a fluid-filled loop
• Paucity of colonic gas (complete obstruction)
• Normal radiographs do NOT exclude SBO (up to 20% of confirmed SBO cases have normal or non-specific plain film findings)

6.3 Management of Adhesive Small Bowel Obstruction

Initial Management (All Patients)

All patients with SBO should receive the following initial management simultaneously with the diagnostic workup:^{1 2}

1. NPO (nil per os)
2. IV fluid resuscitation — patients with SBO may have significant volume depletion from vomiting, third-spacing, and reduced oral intake. Isotonic crystalloid (LR or NS) with electrolyte monitoring and repletion
3. Nasogastric tube (NGT) decompression — for patients with persistent vomiting, significant distension, or complete obstruction. NGT reduces aspiration risk, relieves symptoms, and may facilitate resolution
4. Electrolyte monitoring and correction — hypokalemia, hyponatremia, hypochloremic metabolic alkalosis from vomiting are common
5. Foley catheter — monitor urine output for adequacy of resuscitation
6. Serial abdominal examinations — every 4–8 hours to monitor for signs of clinical deterioration (increasing tenderness, peritoneal signs, fever, tachycardia)

Indications for Urgent/Emergent Surgery

The following findings mandate operative intervention without a trial of conservative management:^{1 2 3}

Conservative Management — Trial of Non-Operative Management

For patients with adhesive SBO without signs of strangulation, closed-loop obstruction, or peritonitis, a trial of conservative (non-operative) management is appropriate.^{1 2}

Protocol:

1. NPO, IV fluids, NGT decompression, serial examinations (as above)
2. Duration of conservative trial: 24–72 hours. Most patients who will resolve with conservative management do so within 24–48 hours. Evidence suggests that conservative management beyond 72 hours without resolution is associated with increased complications
3. Partial SBO (passing some flatus, air in colon on imaging) has a higher spontaneous resolution rate (~65–80%) compared to complete SBO (~20–40%)

Criteria for successful conservative management:

• Resolution of pain
• Passage of flatus and/or stool
• Decrease in NGT output (<200 mL/8 hours)
• Tolerance of oral intake
• Resolution of distension

Water-Soluble Contrast Challenge (Gastrografin)

The water-soluble contrast challenge (using Gastrografin/diatrizoate meglumine) serves a dual diagnostic and therapeutic purpose in adhesive SBO.^{1 2 4}

Protocol:

1. Administer 50–100 mL of Gastrografin through the NGT (clamp NGT for 2 hours after administration)
2. Obtain an abdominal X-ray at 8–24 hours (historically at 24 hours; more recent evidence supports earlier imaging at 8 hours)
3. Assess whether contrast has reached the cecum/colon

Interpretation:

Therapeutic Effect:

Gastrografin is a hyperosmolar, water-soluble contrast agent that:

• Draws fluid into the bowel lumen (osmotic gradient) — 1,900 mOsm/L
• Reduces bowel wall edema
• Stimulates peristalsis
• Multiple meta-analyses have demonstrated that Gastrografin reduces the need for surgery (NNT approximately 5–7) and reduces hospital stay by 1–2 days, though it does NOT reduce mortality or complication rates when surgery is needed⁴

Contraindications to Gastrografin challenge:

• Signs of strangulation or peritonitis
• Suspected or confirmed perforation (Gastrografin is water-soluble and safe in this regard, unlike barium; however, if perforation is present, operative management is indicated)
• Complete obstruction with clear surgical indication
• Allergy to iodinated contrast

6.4 Surgical Management of SBO

When operative intervention is indicated:

• Laparoscopic approach is preferred when feasible (single adhesive band, prior laparoscopic surgery, limited adhesions expected). Benefits include shorter hospital stay, less wound complications, and faster recovery
• Open laparotomy is indicated for dense adhesions, multiple prior operations, hemodynamic instability, or when laparoscopy is technically not feasible
• Adhesiolysis: Lysis of adhesions to relieve obstruction
• Bowel resection: Required for non-viable bowel (absent peristalsis, absent mesenteric pulsation, dark discoloration that does not improve with warm saline and time). Primary anastomosis is generally performed; diversion may be needed in hemodynamically unstable patients or when bowel viability is questionable
• Assessment of bowel viability: In addition to visual inspection, intraoperative assessment may include Doppler interrogation of mesenteric vessels, fluorescein/indocyanine green (ICG) fluorescence imaging, or Wood lamp examination after IV fluorescein injection

7. Large Bowel Obstruction

7.1 Etiology

Large bowel obstruction (LBO) accounts for approximately 25% of all mechanical bowel obstructions.⁵

7.2 Diagnosis

Clinical Presentation

• Progressive abdominal distension (more pronounced than in SBO)
• Constipation progressing to obstipation
• Crampy abdominal pain (may be less severe than SBO)
• Late: nausea/vomiting (may be feculent)
• Competent ileocecal valve: Closed-loop obstruction; cecal distension is the most dangerous concern — cecal diameter >12 cm carries significant risk of perforation
• Incompetent ileocecal valve: Decompression into small bowel occurs; less risk of perforation but may mimic SBO clinically

CT Findings

CT abdomen/pelvis with IV contrast (rectal contrast may be considered but is not mandatory):

• Dilated colon proximal to the obstruction (>6 cm; cecum >9 cm concerning, >12 cm high perforation risk)
• Decompressed distal colon/rectum
• Transition point identifying the site and likely cause
• “Bird beak” or “whirl” sign in volvulus
• Colonic mass/apple-core lesion in malignancy
• Assess for signs of ischemia (pneumatosis, absent wall enhancement, portal venous gas)

7.3 Sigmoid Volvulus

Sigmoid volvulus results from rotation of the sigmoid colon around its mesenteric axis, causing closed-loop obstruction. It is more common in elderly, institutionalized, and neuropsychiatric patients, and is associated with chronic constipation, high-fiber diet, and a long redundant sigmoid colon.^{5 6}

Diagnosis:

• Plain radiograph: Classic “coffee bean” or “bent inner tube” sign — massively dilated sigmoid loop pointing toward the right upper quadrant; loss of haustrations; “northern exposure” sign. Diagnostic in approximately 60% of cases
• CT: “Whirl sign” (twisted mesentery and vessels at the base of the volvulus); “bird beak” sign (tapering of the bowel at the point of torsion); massively dilated sigmoid. More sensitive and specific than plain films

Management:

Endoscopic Decompression Technique:

1. Rigid or flexible sigmoidoscopy without bowel preparation
2. Advance the endoscope through the twisted segment — sudden rush of gas and liquid stool confirms successful decompression
3. Examine the mucosa for signs of ischemia (dusky, necrotic mucosa) — if gangrene is suspected, abort endoscopy and proceed to surgery
4. Place a rectal tube through the decompressed segment, secure with tape
5. Irrigate and leave tube to gravity drainage for 24–48 hours

7.4 Cecal Volvulus

Cecal volvulus results from axial twisting of the cecum, ascending colon, and terminal ileum. Unlike sigmoid volvulus, it typically occurs in younger patients (40s–50s) and requires a mobile cecum (insufficient fixation to the retroperitoneum).^{5 6}

Types:

• Axial torsion (true volvulus, ~70%): Rotation around the long axis of the cecal mesentery
• Cecal bascule (~30%): Anterior and superior folding of the cecum without axial rotation

Diagnosis:

• Plain radiograph: Dilated, gas-filled cecum displaced to the left upper quadrant or mid-abdomen (“kidney bean” shape)
• CT: Whirl sign at the base, dilated cecum in ectopic position, decompressed ascending colon

Management:

• Endoscopic decompression is generally NOT recommended for cecal volvulus (low success rate <30%, high recurrence)
• Surgical management is the standard of care:
  • Viable cecum: Right hemicolectomy with primary ileocolic anastomosis (preferred) OR cecopexy (suture fixation of the cecum to the retroperitoneum — higher recurrence rate but considered in high-risk patients)
  • Gangrenous or perforated cecum: Right hemicolectomy; primary anastomosis vs ileostomy depending on patient stability and contamination

7.5 Ogilvie Syndrome (Acute Colonic Pseudo-Obstruction)

Ogilvie syndrome is a functional, non-mechanical dilation of the colon (primarily the cecum and right colon) occurring most commonly in hospitalized, elderly, or post-surgical patients. It results from an imbalance of autonomic innervation (sympathetic overactivity/parasympathetic suppression).^{5 7}

Risk Factors: Recent surgery (especially orthopedic, cardiac), critical illness, electrolyte abnormalities (hypokalemia, hypomagnesemia, hypocalcemia), opioids, anticholinergics, neurological disease, spinal cord injury

Diagnosis:

• Massive colonic distension on imaging WITHOUT a mechanical obstructing lesion
• CT (or water-soluble contrast enema) to exclude mechanical obstruction is essential before treatment
• Cecal diameter is the key measurement — perforation risk increases significantly when cecal diameter exceeds 12 cm or when distension has been present for >3–4 days

Management — Stepwise Approach:

8. Acute Diverticulitis

8.1 Epidemiology

Diverticulitis is the most common complication of colonic diverticulosis, occurring in approximately 4% to 5% of patients with diverticulosis. It results from microperforation of a diverticulum, leading to pericolic inflammation, abscess formation, or free perforation. Left-sided (sigmoid) diverticulitis predominates in Western populations; right-sided diverticulitis is more common in Asian populations.^{8 9}

8.2 Diagnosis

CT Abdomen/Pelvis with IV Contrast

CT is the gold standard for diagnosing acute diverticulitis and assessing the presence and extent of complications.⁸

CT Findings:

8.3 Hinchey Classification

The Hinchey classification is the standard system for grading the severity of complicated diverticulitis and guides surgical decision-making.^{8 9 10}

8.4 Management of Uncomplicated Diverticulitis

Antibiotics vs No Antibiotics

Traditionally, all patients with acute diverticulitis received antibiotic therapy. However, landmark randomized controlled trials have challenged this practice for uncomplicated diverticulitis.^{8 11}

DIABOLO Trial (2017) — Key Findings:

Current Recommendations for Uncomplicated Diverticulitis:

Admission Criteria

• Inability to tolerate oral intake
• Significant comorbidities (diabetes, immunosuppression, renal failure)
• Failed outpatient management
• Signs of complicated diverticulitis (abscess, peritonitis, obstruction)
• Unreliable social situation or follow-up

Inpatient Antibiotic Regimens

8.5 Management of Complicated Diverticulitis

Abscess (Hinchey Ib/II)

Perforation with Peritonitis (Hinchey III/IV)

Patients with generalized peritonitis require emergent surgical intervention after appropriate resuscitation.^{8 9 10}

Surgical Options:

8.6 Indications for Elective Sigmoid Resection After Diverticulitis

The traditional recommendation for elective sigmoidectomy after 2 episodes of uncomplicated diverticulitis has been largely abandoned. Current evidence-based recommendations:^{8 9}

References