small bowel obstruction
· General considerations
o Small bowel obstruction, as the term is used here, is due to physical and organic changes which produce mechanical obstruction to the passage of the bowel contents somewhere in the small bowel
o The bowel proximal to the point of obstruction dilates with swallowed air and secreted fluid,
§ Vomiting may release some of the proximal bowel contents and reduce the amount of proximal dilation
o The bowel hyperperistalses
o Bowel distal to the point of obstruction (i.e. colon and sometimes distal small bowel) empties over time
o Strangulation of the bowel may result from vascular compromise of the affected loops and is a cause of increased mortality
· Causes
o Overwhelmingly, the most common cause of a mechanical small bowel obstruction are adhesions related to prior surgery (60%)
§ The most common prior surgeries associated with a subsequent SBO include appendectomy, colorectal surgery and gynecologic surgery
§ Bowel may become kinked under an adhesion
§ The obstruction is frequently partial or intermittent
o Hernias
§ Most often femoral or inguinal
o Intussusception
o Volvulus
o Tumor, either primary or metastatic
o Wall lesions such as leiomyomas or strictures
o Crohn’s disease
o Foreign bodies
o Gallstones
§ Such as in gallstone ileus (which is actually a mechanical obstruction, usually at the ileocecal valve)
· Clinical findings
o Abdominal pain and distension
§ Most marked in patients with distal SBO although its onset in distal obstructions is later in the course of the disease than in proximal obstruction
§ Typically colicky in nature and progressively worsening over time
o Nausea
o Vomiting
§ An earlier sign of a proximal than a distal obstruction
§ Fluid and electrolyte imbalances from vomiting increase mortality
o Constipation
o History of prior abdominal or pelvic surgery
o Bowel sounds are hyperactive and high-pitched
§ Absence of bowel sounds may indicate bowel ischemia or peritonitis
· Imaging findings
o Conventional radiography is the study of first choice
§ Loops proximal to the point of obstruction will become dilated and fluid-filled
· Usually greater than 2.5-3 cm in size
§ Differential height of air-fluid levels in the same loop of small bowel no longer considered reliable sign of mechanical SBO
§ Absence of, or disproportionately smaller amount of, gas in the colon, especially the rectosigmoid
§ Loops of small bowel may arrange themselves in a step-ladder configuration from the left upper to the right lower quadrant in a distal SBO
§ Mostly fluid-filled loops of bowel may demonstrate a string-of-beads sign caused by the small amount of visible air in those loops
Small Bowel Obstruction. Supine view of the abdomen (left) shows several dilated loops of small bowel
in the upper abdomen. The small bowel is
disproportionately dilated compared the the large bowel
which is collapsed. The upright view (right)
demonstrates multiple air-fluid levels in the dilated loops
in a typical configuration of a small bowel obstruction.
The patient had previous bowel surgery.
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