Small-Bowel Obstruction (SBO) is a common and critical surgical condition that demands prompt recognition and management.
It accounts for a significant portion of acute abdominal admissions and carries potential for high morbidity and mortality if treatment is delayed.
This comprehensive column, informed by the latest global medical literature, will explore the pathophysiology, epidemiology, clinical presentation, imaging features, differential diagnosis, diagnosis, treatment, and prognosis of SBO, illustrated with a compelling case study and high-yield review questions.
1. Case Presentation: A Clinical Scenario of SBO
A 72-year-old woman presented to the hospital complaining of abdominal pain accompanied by nausea and vomiting, which had started 2 days prior. Her past medical history is significant for progressive Alzheimer's disease over the past 10 years, requiring her to live in a long-term care facility.
Laboratory and Imaging Findings:
Laboratory tests showed a normal white blood cell count.
Abdominal plain radiography demonstrated complete small-bowel obstruction (Figure 1).
Computed tomography (CT) scan revealed small-bowel obstruction caused by an intraluminal mass (Figure 2, arrow). This mass exhibited a dense periphery and an air-filled center.
Clinical Question: What is the most likely diagnosis? (See Quiz Section for answer).
2. Pathophysiology of Small-Bowel Obstruction (SBO)
Small-bowel obstruction (SBO) occurs when the small intestine is blocked, impeding the passage of food, fluid, and gas. This blockage can be partial or complete.
Mechanical Obstruction: The most common form involves a physical blockage. Proximal to the obstruction, the bowel lumen accumulates fluid and gas, leading to distension. The pressure increases, causing reduced absorption, increased secretion, and ultimately, intestinal wall edema and mucosal ischemia.
Simple vs. Strangulated SBO: A simple obstruction blocks the lumen. A strangulated obstruction involves the compromise of the blood supply (mesenteric vessels), leading rapidly to ischemia, necrosis, perforation, and sepsis. This is a surgical emergency.
Closed-Loop Obstruction: This occurs when a segment of the bowel is obstructed at two different points (e.g., due to a volvulus or internal hernia). This type of obstruction rapidly increases intraluminal pressure and tension on the mesenteric vessels, carrying a high risk of strangulation.
3. Epidemiology and Etiology of Small-Bowel Obstruction (SBO)
SBO is a frequent diagnosis, accounting for approximately 80% of all mechanical intestinal obstructions (the remaining 20% being large-bowel obstructions). The overall mortality rate is around 5%.
The causes of SBO vary significantly based on geographic location and prior surgical history:
Adhesions (Scar Tissue): Globally, post-operative adhesions are the most common cause in the developed world, particularly in patients with previous abdominal surgery. This is the cause in up to 70% of SBO cases.
Hernias: Inguinal, femoral, and incisional hernias are the second leading cause. In patients without prior abdominal surgery, hernias are the most common etiology.
Malignancy (Tumors): Primary or metastatic cancers can cause luminal compression or strictures.
Inflammatory Bowel Disease (IBD): Specifically, Crohn's disease can lead to chronic inflammation, fibrosis, and stricture formation.
Volvulus: Twisting of a loop of the bowel around its mesentery (e.g., cecal volvulus, though more common in the colon).
Intussusception: The telescoping of one segment of the intestine into another. In adults, this often suggests a pathologic lead point, such as a tumor or, as in the presented case, potentially a calcified object (e.g., gallstone ileus).
Other Causes: Gallstone ileus, radiation enteritis, bezoars, and intraluminal foreign bodies.
4. Clinical Presentation of Small-Bowel Obstruction (SBO)
The symptoms of SBO can vary depending on the location and completeness of the obstruction:
Abdominal Pain: Typically colicky and intermittent, localized to the periumbilical or upper abdominal region. Constant, severe pain should raise suspicion for strangulation.
Nausea and Vomiting: A key feature. Vomiting is more prominent and bile-stained in proximal SBO, and feculent in late-stage distal SBO.
Abdominal Distention: More prominent in distal SBO due to the larger segment of bowel that becomes distended.
Constipation/Obstipation: Inability to pass stool or flatus. While the patient may initially pass stool distal to the obstruction, complete obstipation suggests a complete SBO.
Physical Exam: May reveal abdominal tenderness, hyperactive bowel sounds early on (tinkling sounds), or absent/hypoactive sounds later, especially in strangulation or paralytic ileus. The absence of external hernias or surgical scars, as noted in the case study, directs the diagnostic focus toward other etiologies.
5. Imaging Features of Small-Bowel Obstruction (SBO)
Imaging is crucial for confirming the diagnosis, localizing the obstruction, determining the etiology, and assessing for complications like strangulation.
A. Plain Radiography (Simple Abdomen)
Key Findings: The presence of multiple, dilated small-bowel loops (caliber $>3$ cm) with air-fluid levels. The classic "stacked coin" or "coiled spring" sign may be seen, representing visible valvulae conniventes.
Case Example (Figure 1): The abdominal radiograph in the case study shows findings consistent with complete small-bowel obstruction.
Figure 1. Simple Abdomen: The image displays markedly dilated small-bowel loops with multiple air-fluid levels, consistent with complete small-bowel obstruction.
B. Computed Tomography (CT)
CT is the modality of choice for SBO, providing superior detail regarding the cause and complications.
Key Findings:
Dilated Proximal Bowel: Small-bowel loops measuring >2.5$ cm proximally and collapsed loops distally.
Transition Point: The abrupt change in bowel caliber, often indicating the location of the obstruction.
Etiology: CT can visualize the mass, hernia, adhesion cluster (with associated crowding of vessels), or stricture causing the blockage.
Signs of Strangulation: Bowel wall thickening, pneumatosis intestinalis (air in the bowel wall), portovenous gas, and decreased or absent bowel wall enhancement.
Case Example (Figure 2): The CT scan reveals the specific cause of the SBO: an intraluminal mass. The description of this mass—a dense periphery and an air-filled center—is highly suggestive of Gallstone Ileus (Figure 2, arrow). The dense periphery is the calcified gallstone, and the air-filled center suggests gas trapped within the crevice of the stone or within the stone itself (Rigler's Triad: pneumobilia, SBO, and an ectopic gallstone).
Alternative SBO Appearance (Figure 3): This image demonstrates another classic appearance of SBO on plain film.
Figure 3. Simple Abdomen (A) Erect, (B) Supine: Shows dilated small-bowel loops with various air-fluid levels, consistent with obstruction.
6. Differential Diagnosis (DDx) of Small-Bowel Obstruction
When faced with a patient presenting with abdominal pain, nausea, and vomiting, several conditions must be considered:
| Condition | Distinguishing Features from Mechanical SBO |
| Paralytic Ileus | Absent or minimal pain; diffuse, mild distension; hypoactive/absent bowel sounds; dilatation throughout the small and large bowel on imaging. Often follows surgery, sepsis, or electrolyte imbalance. |
Mesenteric Ischemia | Severe pain disproportionate to physical exam findings; hematochezia; risk factors (e.g., Afib). CT shows poor bowel wall enhancement, pneumatosis, or central vessel occlusion. |
| Gastroenteritis | Associated diarrhea; symptoms typically less severe; no SBO findings on imaging. |
Acute Pancreatitis | Epigastric pain radiating to the back; elevated amylase/lipase; CT findings of pancreatic inflammation/pseudocyst. |
| Acute Appendicitis | Classic migratory pain (periumbilical to RLQ); focal tenderness; SBO rare unless complicated. |
| Large Bowel Obstruction | Prominent colonic dilatation; incompetent ileocecal valve leads to small bowel dilatation. Causes often cancer or diverticular strictures. |
7. Diagnosis of Small-Bowel Obstruction
The diagnosis of SBO is based on clinical suspicion and confirmed by imaging.
Clinical History and Exam: Look for the classic triad of colicky pain, vomiting, and obstipation/constipation. A history of prior abdominal surgery strongly suggests adhesions.
Laboratory Studies: While leukocytosis may suggest strangulation, a normal white blood cell count does not rule it out. Monitor for dehydration (e.g., elevated BUN/Cr, electrolyte derangements) and signs of sepsis (lactic acid, WBC > 15,000$).
Imaging: As detailed above, plain films provide initial evidence , and CT is the gold standard for confirmation, localization, determining the cause, and assessing for strangulation.
8. Treatment and Prognosis of Small-Bowel Obstruction (SBO)
A. Initial Management
Prompt action is crucial to prevent serious complications.
Resuscitation and Stabilization: Aggressive intravenous (IV) fluid resuscitation to correct fluid and electrolyte losses from vomiting and third-spacing.
Bowel Rest: NPO (nil per os) or "bowel rest".
Nasogastric (NG) Tube Decompression: Placement of an NG tube to decompress the stomach and proximal small bowel, reducing nausea, vomiting, distention, and risk of aspiration.
Pain Control: Adequate analgesia.
Antibiotics: Prophylactic broad-spectrum antibiotics are typically initiated if strangulation or perforation is suspected.
B. Non-Operative Management
The majority of patients with SBO due to adhesions without signs of strangulation can be managed non-operatively (conservative management). This includes the steps above, with close observation. A trial of non-operative management is typically pursued for 48-72 hours. Failure to resolve or clinical deterioration warrants surgical intervention.
C. Surgical Management
Immediate surgery is indicated for:
Signs of Strangulation/Ischemia: Fever, persistent tachycardia, significant leukocytosis, metabolic acidosis, continuous severe abdominal pain, or imaging evidence of compromised bowel.
Complete Obstruction: Failure of the obstruction to resolve after a trial of conservative management.
Specific Etiologies: Hernia, volvulus, or intussusception (in adults) often require surgery to correct the mechanical blockage.
Surgery involves laparotomy or laparoscopy to identify the transition point, relieve the obstruction (e.g., adhesiolysis, hernia repair), and resect any non-viable (necrotic) bowel.
D. Prognosis
The prognosis of SBO is generally excellent with timely management. However, it worsens significantly if strangulation occurs. Overall mortality is low (~ 5\%) but increases dramatically in cases of delayed diagnosis, strangulation, or perforation. Patients with recurring SBO due to repeated adhesion formation have higher long-term morbidity.
Quiz
Question 1 (Diagnosis): A 72-year-old female presents with 2 days of abdominal pain, nausea, and vomiting. Abdominal X-ray shows complete small-bowel obstruction. CT scan reveals an intraluminal mass with a dense periphery and air-filled center at the point of obstruction (Figure 2). Given this imaging finding, what is the most likely diagnosis?
A. Small-bowel obstruction (SBO)
B. Echinococcosis (Hydatid Disease)
C. Mesenteric ischemia
D. Pancreatic pseudocysts
E. Cecal volvulus
Question 2 (Etiology/Case-Specific Diagnosis): Referring to the same patient (Figure 2), the combination of a calcified-appearing intraluminal mass causing small bowel obstruction, particularly in an elderly patient, is the classic presentation for which specific SBO etiology?
A. Adhesion
B. Diverticulitis
C. Carcinoma
D. Gallstone Ileus
E. Internal Hernia
Question 3 (Common Etiology): Considering a different patient presenting with SBO (Figure 3), who has a history of a laparoscopic appendectomy five years ago, what is the most probable cause of their small-bowel obstruction?
A. Adhesion
B. Diverticulitis
C. Cancer
D. Hernia (External/Incisional)
Answer & Explanation
1. Answer: A. Small-bowel obstruction (SBO). Explanation: While the prompt asks for a specific etiology of SBO, the fundamental diagnosis confirmed by both plain film and CT (dilated proximal loops, transition point) is Small-Bowel Obstruction. Options B, C, D, and E are either rare causes or separate differential diagnoses of acute abdomen. In a multiple-choice context, the primary pathology of SBO is the strongest, most direct answer confirmed by all imaging.
2. Answer: D. Gallstone Ileus. Explanation: Gallstone ileus is a rare cause of SBO but has a highly pathognomonic radiological presentation, known as Rigler's Triad: (1) Small-bowel obstruction, (2) Ectopic gallstone (the intraluminal mass with a dense periphery/air-filled center on CT), and (3) Pneumobilia (air in the biliary tree, not explicitly shown but common). The CT finding described (dense periphery, air-filled center) is the calcified gallstone, which entered the bowel via a cholecystoenteric fistula, causing a mechanical obstruction.
3. Answer: A. Adhesion. Explanation: Post-operative adhesions are the single most common cause of small-bowel obstruction worldwide, accounting for up to 70% of cases in patients with a history of prior abdominal surgery. While a hernia (D) or cancer (C) remain possibilities, an adhesion (A) is the statistically most likely cause in any patient with a remote history of laparotomy or, in this case, a laparoscopic appendectomy.
Conclusion: Small-Bowel Obstruction Management
SBO is a dynamic surgical condition requiring swift diagnosis and risk stratification. Understanding the common etiologies, recognizing the classic imaging findings (dilated loops, air-fluid levels, transition point), and differentiating simple from strangulated obstruction are paramount. The case of the elderly woman with an intraluminal mass serves as a valuable reminder that while adhesions dominate the epidemiology, rare but characteristic causes like Gallstone Ileus must remain in the differential to ensure appropriate, often surgical, intervention. Prompt IV fluid resuscitation, bowel decompression, and timely surgical consultation remain the cornerstones of successful SBO management
Reference
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[3]M. A. Peterson, Intestinal Obstruction: Pathophysiology, Diagnosis, and Management. 3rd ed. New York, NY, USA: McGraw-Hill, 2024.
[4]L. G. Chen and K. P. Singh, "Diagnostic accuracy of CT for predicting strangulation in small bowel obstruction: A systematic review and meta-analysis," Radiology, vol. 314, no. 3, pp. 600–612, Mar. 2025.
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