Findings: Small bowel obstruction secondary to right indirect inguinal hernia

Objectives:

• To learn the definition of a small bowel obstruction, high grade small bowel obstruction

• To review common etiologies of small bowel obstruction

• To practice following small bowel to assess for severity, etiology, signs of ischemia

Protocolling:

• Contrast Enhanced CT, no oral contrast required

• Can give oral contrast if suspected to be only partial obstruction

Key points:

• Abdominal Xray is only approximately 50% sensitive for SBO

  • Difficult to exclude - can appear as fluid filled loops or nonspecific bowel gas pattern

• Role of CT scan is to answer the following questions:

  • Is the small bowel obstructed?

  • How severe is the obstruction? (i.e. high grade?)

  • Is an etiology apparent on imaging?

  • Are there signs of ischemia?

• Small bowel obstruction

  • Proximally dilated loops (>2.5 - 3 cm)

  • Distally normal or collapsed small bowel loops.

  • Passage of oral contrast can distinguish complete vs. incomplete.

• Ileus = dilatation of large and small bowel with no transition point

• High grade obstruction

  • Distally collapsed small bowel loops less than ½ the caliber of proximally dilated loops

• Finding the transition point:

  • Follow small bowel anterograde or retrograde, depending on suspected location of transition point

  • Use reformats to help follow small bowel

  • Don’t make any assumptions - follow bowel from loop to loop only when 100% sure that the lumens connect

  • “Small bowel feces sign” often identified just proximal to obstruction

• Determining the etiology (assess the transition point):

  • Adhesion - most common. Diagnosis of exclusion (abrupt change of caliber without findings to suggest another cause)

  • Hernias - external (inguinal, femoral, obturator, umbilical, incisional, etc), internal (paraduodenal, transmesenteric, etc)

  • Crohn’s disease - from acute thickening, strictures, adhesions/hernias

  • Tumor - adenocarcinoma/mets. Look for focal mass, asymmetric thickening, evidence of other metastatic disease.

  • Intussusception - bowel within bowel with or without mesenteric fat

  • Gallstone Ileus - Rigler’s triad (pneumobilia, SBO, gallstone). Bouveret’s syndrome is basically proximal gallstone ileus.

  • Other: endometriosis, bezoar, radiation enteritis, etc.

• Assess for ischemia (see intestinal ischemia case)

Suggested resource: “Silva AC, Pimenta M, Guimaraes LS. Small Bowel Obstruction: What to look for. RadioGraphics 2009; 29;423-39.”