Small Bowel Obstruction

Eva Ilse Rubio, MD

DIFFERENTIAL DIAGNOSIS

Common

Appendicitis
Adhesions
Ileocolic Intussusception
Midgut Volvulus
Inflammatory Bowel Disease (Crohn Disease)
Incarcerated Inguinal Hernia

Less Common

Hirschsprung Disease
Meconium Plug Syndrome (Small Left Colon Syndrome)
Meckel Diverticulum
Jejunoileal Atresia
Meconium Ileus
Gastrointestinal Duplication Cysts

Rare but Important

Distal Intestinal Obstructive Syndrome

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

In neonates, differentiate between high (proximal) and low (distal) obstruction
- Common causes of proximal obstruction
  - Malrotation/midgut volvulus
  - Duodenal atresia
  - Duodenal stenosis/web
  - Diagnostic work-up starts with upper GI
- Common causes of mid-bowel obstruction
  - Jejunal atresia/web
  - Volvulus ± malrotation
  - Diagnostic work-up usually involves upper GI and contrast enema
- Low (distal) obstruction
  - Hirschsprung disease
  - Meconium plug syndrome (small left colon syndrome)
  - Ileal atresia
  - Meconium ileus
  - Work-up starts with contrast enema
Common differential considerations for obstruction in older children
- Appendicitis
- Adhesions
- Intussusception
- Incarcerated inguinal hernia
- Inflammatory bowel disease
- Meckel diverticulum

Helpful Clues for Common Diagnoses

Appendicitis
- Radiograph
  - Appendicitis should be considered with appendicolith on plain film
  - Classic small bowel obstruction is common presentation: Dilated loops, multiple air-fluid levels on upright or decubitus views
  - Early appendicitis may be subtle with distal bowel gas and stool, scattered air in small bowel
- Ultrasound
  - Iliac artery/vein useful landmark for locating appendix, which often lies near/over vessels
  - Noncompressible blind-ending tube, ≥ 7 mm diameter, echogenic periappendiceal fat
  - If significant amount of free intraperitoneal fluid, suspect perforation
- CT
  - Inflamed, hyperemic tubular structure; does not fill with oral contrast
  - Look for signs of longstanding/perforated appendicitis: Free fluid, free air, inflammatory phlegmon
Adhesions
- Almost never directly visualized; diagnosis made intraoperatively
- Wide range of severity on any modality (radiograph, CT, US)
  - Nonspecific increased small bowel air with fluid levels, distal bowel gas if mild/partial/intermittent obstruction
  - Dilated small bowel loops, absent distal gas, air-fluid levels if high-grade or complete obstruction
Ileocolic Intussusception
- Majority of cases occur between age 3 months to 3 years
  - If well outside this age range or recurrent, consider pathologic lead point
- Radiograph
  - Bowel gas pattern ranges from nonspecific to frank obstruction
  - Intussusceptum may be identifiable as right lower quadrant soft tissue density
- Ultrasound is sensitive and specific tool to confirm or exclude intussusception
  - Alternating hypo-/hyperechoic rings
Midgut Volvulus
- Must be excluded in patients with bilious emesis
- Bowel gas pattern ranges from nonspecific/normal to ominously dilated loops of proximal bowel with paucity of distal bowel gas
Inflammatory Bowel Disease (Crohn Disease)
- Findings may manifest anywhere from mouth to anus
- CT
  - Segmental, circumferentially thickened bowel wall with luminal narrowing
  - Fatty proliferation, engorged vessels, inflammatory stranding around bowel
  - Abscesses, especially perirectal
- Fluoroscopic
  - “String” sign of narrowed lumen
  - Fistulae to skin or adjacent bowel loops
  - Thickened mucosal folds
  - Cobblestone pattern: Longitudinal and transverse ulcers
Incarcerated Inguinal Hernia
- Diagnosed with loops of bowel in scrotum
  - Detected clinically, easily confirmed by ultrasound

Helpful Clues for Less Common Diagnoses

Hirschsprung Disease
- Abnormal rectosigmoid ratio (R/S diameter < 1) on contrast enema may be clue
Meconium Plug Syndrome (Small Left Colon Syndrome)
- Contrast enema: Transition point between dilated proximal and narrow distal colon
Meckel Diverticulum
- Mimics appendicitis: Thickened, blind-ending tubular structure in abdomen/pelvis
- Rule of 2s: 2% of population, within 2 feet of ileocecal valve, symptoms before age 2
- Tc-99m pertechnetate scan demonstrates focus of activity in lower abdomen
Jejunoileal Atresia
- Ileal atresia contrast enema: Microcolon
- Jejunal atresia contrast enema: Normal caliber colon
  - If microcolon on contrast enema, expect presence of other distal atresias
Meconium Ileus
- Radiograph: Distal bowel obstruction
- Fluoroscopy: Microcolon, meconium pellets in terminal ileum
  - Meconium ileus not excluded until contrast refluxes into terminal ileum
Gastrointestinal Duplication Cysts
- Most common location is terminal ileum
- Ultrasound: Round, hypoechoic structure with bowel wall signature

Helpful Clues for Rare Diagnoses

Distal Intestinal Obstructive Syndrome
- Meconium ileus equivalent
- Must be suspected with small bowel obstruction in cystic fibrosis population

Image Gallery

Frontal radiograph shows mildly dilated loops of small bowel with air-fluid levels

on the the upright view. Note the appendicoliths

in the right lower quadrant.

Axial CECT in the same patient shows the large abscess

resulting from perforation. Note 1 of several appendicoliths

. The patient presented after 8 days of fever.

(Left) Coronal CECT shows numerous, rim-enhancing, loculated fluid collections

interspersed among the loops of bowel, consistent with intraperitoneal abscesses resulting from a ruptured appendicitis. Note the sizable appendicolith