Fact-sheet: Small bowel obstruction


Updated on 04/07/2026 at 8:43 AM

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Definition

Small bowel obstruction: obstruction or blockage of at least one segment of the Small bowel.

A classic distinction is made between:

  • mechanical (organic) obstruction, related to an obstacle or blockage resulting from intrinsic or extrinsic narrowing of the bowel lumen,
  • and functional obstruction (ileus), related to impaired motility.

Clinical features

Four symptoms whose combination is highly suggestive:

  • Abdominal pain, often the first sign.
  • Vomiting, early in Small bowel obstruction.
  • Cessation of passage of flatus and stool, a major and definitive sign.
  • Abdominal distension, often delayed.

Auscultation: borborygmi in obstructive forms, or "sepulchral" silence in cases of strangulation.

Clinical examination: look for surgical scars and examine the hernial orifices.

Laboratory findings

Few specific laboratory findings

CRP to assess associated inflammation

Clear clinical and laboratory evidence of bowel compromise may prompt an aggressive management approach, particularly when ischemia is suspected

Radiography

Plain abdominal radiograph. Obsolete. Low diagnostic yield compared with CT

  • Dilated Small bowel loops (transverse diameter > 3 cm) with a central distribution.
  • Numerous air-fluid levels, wider than tall.
  • String-of-pearls sign: small aligned gas bubbles within fluid-filled loops, seen on a supine radiograph.
  • Pneumoperitoneum: in cases of perforation. Free air under the diaphragm. Rigler's sign: visualization of both sides of the bowel wall.

Retrograde contrast studies (enemas): therapeutic value in the reduction of intussusception.

Ultrasound

First-line examination in children and often preferred in pregnant women.

  • Mechanical obstruction: dilated fluid-filled loops (> 25-30 mm) with increased peristalsis proximal to a transition zone, beyond which the downstream loops are collapsed.
  • Signs of severity (strangulation/ischemia): circumferential bowel wall thickening, loss of wall stratification, disappearance of mucosal folds, intraperitoneal fluid, and absent peristalsis.
  • Doppler: absence of Doppler flow in the bowel wall is a sign of potentially irreversible ischemia.

Specific signs:

  • "Target" or "pseudo-Kidney" sign for intussusception.
  • Whirlpool sign for volvulus.

CT

Reference examination (Se 95%, Sp 96% for high-grade obstructions).

Acquisition without oral contrast (which may mask signs of ischemia) and with IV contrast injection at the portal venous phase.

Positive and topographic diagnosis:

  • Small bowel dilation > 25 mm.
  • Identification of a transition zone between dilated upstream loops and collapsed downstream loops.
  • Small bowel feces sign: gas bubbles mixed with particulate fecal material within the small bowel, just proximal to the obstruction.

Signs of severity (strangulation and ischemia):

  • Lack of bowel wall enhancement (highly specific sign of ischemia).
  • Bowel wall thickening > 3 mm (edema) or paper-thin wall < 1 mm (acute ischemia).
  • Pneumatosis intestinalis, portal venous gas, or mesenteric venous gas.
  • Closed-loop obstruction: "C"- or "U"-shaped loop configuration, with convergence of mesenteric vessels toward the torsion site.
  • Whirl sign indicating volvulus.

Adynamic or paralytic ileus: diffuse dilation of the small bowel and colon without an identifiable transition zone.

Distal intestinal obstruction syndrome (DIOS): common in cystic fibrosis, related to thickening of fecal content in the terminal ileum.

MRI

Reserved for follow-up of chronic conditions such as Crohn disease.

Limited use in the emergency setting due to its duration and the need for full patient cooperation.

Classification

Mechanical obstructions can be classified according to their mechanism:

  • Extrinsic (60-75%): Adhesions and bands (leading cause, often postsurgical), external hernias (15%) or internal hernias.
  • Intrinsic (15%): Tumors (adenocarcinomas, metastases, GIST), Crohn disease, wall hematomas.
  • Intraluminal: Gallstone ileus (calculus migration), bezoards, foreign bodies, parasites.

Differential diagnosis

Aerophagia: excess gas without marked dilation or air-fluid levels.

Colonic obstruction: peripheral dilation, air-fluid levels taller than wide, haustral pattern.