Small Bowel Obstruction
Understand Small Bowel Obstruction in Abdomen Computed Tomography imaging, what it means, and next steps.
30-Second Overview
Dilated proximal small bowel loops with a transition point to collapsed distal bowel; possible closed-loop configuration.
Can progress to ischemia or perforation; needs rapid surgical or conservative management.
benignRate
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Imaging Appearance
Computed Tomography FindingDilated proximal small bowel loops with a transition point to collapsed distal bowel; possible closed-loop configuration.
Clinical Significance
Can progress to ischemia or perforation; needs rapid surgical or conservative management.
Understanding Small Bowel Obstruction
A small bowel obstruction occurs when something blocks the normal flow of food, fluids, and gas through your small intestine. Before we look at how this appears on imaging, let's understand why this condition requires prompt attention.
Dilated bowel loops (＞2.5-3 cm) with a clear transition point where obstruction occurs; closed-loop configuration is a surgical emergency
Here's how accurate CT is at diagnosing small bowel obstruction:
High accuracy for detection and determining cause
Correctly rules out healthy patients
Annual new cases
Think of your small intestine like a garden hose—when it's flowing freely, water passes through easily. But if you step on the hose or create a kink, water backs up behind the blockage. Similarly, when your small bowel is obstructed, everything backs up, causing dilated loops and potentially compromising blood flow.
What Is Small Bowel Obstruction?
Small bowel obstruction (SBO) is a partial or complete blockage of the small intestine that prevents contents from passing through normally. This can be a medical emergency because prolonged obstruction can lead to bowel ischemia (tissue death from lack of blood flow), perforation, and life-threatening infection.
Common Causes:
| Cause | Percentage | Description | |-------|------------|-------------| | Adhesions (scar tissue) | 60-70% | From previous abdominal surgeries | | Hernia | 10-20% | Inguinal, femoral, or incisional | | Cancer/tumor | 5-15% | Primary or metastatic tumors | | Crohn's disease | 5% | Inflammatory narrowing | | Volvulus | 3-5% | Twisting of bowel on itself | | Other | ＜5% | Foreign bodies, bezoars, intussusception |
Why CT is the gold standard:
- Shows the exact location and level of obstruction
- Identifies the cause (adhesions vs. hernia vs. tumor)
- Detects signs of ischemia (compromised blood supply)
- Evaluates for closed-loop obstruction (surgical emergency)
- Rules out alternative diagnoses
How Small Bowel Obstruction Appears on CT
When your doctor orders a CT scan for suspected bowel obstruction, the radiologist looks for specific patterns that confirm the diagnosis and guide treatment decisions.
What Normal Small Bowel Looks Like
Normal small bowel loops appear with diameter less than 2.5 cm. Gas and fluid are evenly distributed throughout the abdomen. No air-fluid levels are visible. The bowel wall is thin and normally enhancing. Mesenteric fat appears clear without stranding.
What Small Bowel Obstruction Looks Like
Dilated proximal small bowel loops measuring ＞3 cm in diameter. Multiple air-fluid levels at different heights (step-ladder sign). Clear transition point where dilated bowel meets collapsed distal bowel. Bowel wall thickening or reduced enhancement may indicate ischemia. Mesenteric fat stranding or swirl suggests closed-loop obstruction.
Key Findings Pattern
When interpreting your CT scan for small bowel obstruction, radiologists look for specific signs that determine urgency:
Key Imaging Findings
Dilated bowel loops ＞3 cm
Small bowel diameter exceeding 3 cm with proximal dilation and distal collapse
Transition point
Clear site where dilated bowel suddenly becomes decompressed, indicating the level and cause of blockage
Small bowel feces sign
Solid fecal-like material mixed with gas in dilated small bowel loops
Closed-loop obstruction
C-shaped or U-shaped dilated bowel loop with two adjacent obstruction points; mesenteric whirl (swirl of vessels)
Bowel wall enhancement abnormalities
Reduced or absent enhancement, wall thickening ＞3 mm, or pneumatosis (air in bowel wall)
When Your Doctor Orders This Test
Here's a typical scenario where a CT scan is ordered for suspected small bowel obstruction:
Clinical Scenario
Common presenting symptoms:
- Cramping abdominal pain (waves of pain as bowel tries to push past blockage)
- Nausea and vomiting (often bilious/green)
- Abdominal distension (bloating, visible enlargement)
- Obstipation (inability to pass gas or stool)
- Dehydration from vomiting and fluid sequestration
Red flags requiring urgent surgical evaluation:
- Fever, tachycardia, hypotension (signs of sepsis)
- Severe, constant pain (suggests ischemia)
- Peritoneal signs (rebound tenderness, guarding)
- Leukocytosis, metabolic acidosis (lab signs of ischemia)
Differential Diagnosis
Several conditions can mimic small bowel obstruction on CT scan:
What Else Could It Be?
History of abdominal surgery. Transition point often in surgical bed. No evidence of hernia or mass. May improve with conservative management if no ischemia.
Visible hernia on CT (inguinal, femoral, umbilical, incisional). Bowel loop trapped in hernia sac. Requires hernia repair with possible bowel resection.
Diffusely dilated small bowel AND colon without transition point. Often post-surgical, due to electrolyte imbalance, medications, or infection. No surgical treatment needed.
Mass lesion at transition point, often in distal small bowel. May have lymphadenopathy or metastases. Requires surgical resection and oncology referral.
Massive colonic dilation without mechanical obstruction. Usually in elderly, hospitalized patients. Treated with neostigmine or decompression, not surgery.
How Accurate Is CT for Small Bowel Obstruction?
The evidence supporting CT as the first-line imaging modality for suspected small bowel obstruction is strong:
CT is highly accurate for diagnosing small bowel obstruction. It correctly identifies 90-95% of true obstructions and correctly rules out obstruction in 85-90% of cases. The addition of coronal reformats improves diagnostic accuracy and helps surgeons better understand the anatomy.
CT signs of ischemia (reduced enhancement, pneumatosis, portal venous gas) have high positive predictive value for bowel compromise. However, clinical correlation is essential because some patients with concerning CT findings may still have viable bowel at surgery.
Beyond confirming obstruction, CT frequently alters clinical management by identifying the specific cause, detecting complications (ischemia, perforation), and revealing alternative diagnoses. This information determines whether patients need surgery or can be managed conservatively.
What Happens Next?
If your CT shows small bowel obstruction, here's the typical care pathway:
What Happens Next?
Initial assessment and stabilization
IV fluids for dehydration, nasogastric tube to decompress stomach, pain control, electrolyte correction. Monitor closely for signs of ischemia or peritonitis.
Determine management approach
Partial SBO without ischemia: conservative trial (NPO, NG tube, IV fluids). Complete SBO, closed-loop, or ischemia: urgent surgical consultation. CT findings guide this critical decision.
Conservative management (if appropriate)
If no ischemia or peritonitis, trial of nonoperative management. Serial exams, repeat CT if clinical deterioration. 70-80% of adhesive partial SBOs resolve without surgery.
Surgical intervention (if indicated)
Exploratory laparoscopy or laparotomy. Lysis of adhesions, hernia repair, bowel resection if necrotic. Source control and restoration of bowel continuity.
Post-treatment follow-up
If managed conservatively, investigate underlying cause if not adhesions. If surgery performed, postoperative follow-up to ensure recovery and discuss prevention of recurrent SBO.
When to Seek Immediate Care
Return to the emergency department immediately if you develop:
- Severe, constant abdominal pain (not cramping)
- Fever ＞101°F (38.3°C)
- Vomiting that won't stop
- Inability to pass gas OR stool after 24 hours
- Abdomen feels hard, rigid, or extremely tender
- Dizziness, fainting, or confusion (signs of sepsis)
Frequently Asked Questions
Can small bowel obstruction resolve without surgery?
Yes, partial obstructions without ischemia often resolve with conservative management (NPO, NG tube, IV fluids). About 70-80% of adhesive partial small bowel obstructions improve without surgery. However, complete obstructions, closed-loop obstructions, or those with ischemia typically require surgery.
What causes adhesions?
Adhesions are bands of scar tissue that form after abdominal surgery. Most people who have abdominal surgery develop some adhesions, but only a small percentage develop obstruction. Adhesions typically develop within the first few months after surgery but can cause problems years later.
Will I need surgery again in the future?
Recurrence rate after adhesive SBO surgery is approximately 15-20% within 5 years. This is why surgeons try to minimize additional surgery when possible. Some patients experience multiple episodes of partial SBO that resolve conservatively before eventually needing definitive surgery.
What is a closed-loop obstruction?
A closed-loop obstruction occurs when a segment of bowel is obstructed at two adjacent points, creating a closed loop. This can happen with adhesions, hernias, or volvulus (twisting). It's dangerous because the trapped bowel continues to secrete fluid and distend, compromising its blood supply and leading to ischemia. This is a surgical emergency.
Can I prevent small bowel obstruction?
If you've had abdominal surgery, you can't completely prevent adhesions, but you may reduce recurrence risk by: staying well-hydrated, eating a high-fiber diet to prevent constipation, avoiding large meals that are hard to digest, and seeking early medical attention if symptoms recur. For hernia-related obstruction, prompt hernia repair before complications occur is preventive.
References
Medical References
This content is referenced from authoritative medical organizations:
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Medical Disclaimer: This information is for educational purposes. Small bowel obstruction can be a surgical emergency. Always seek immediate medical attention for symptoms of bowel obstruction.
Correlate with Lab Results
When Small Bowel Obstruction appears on imaging, doctors often check these lab tests:
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