086. Bowel Obstruction and Volvulus

Small Bowel Obstruction

Causes: adhesions (MCC), hernia, intussusception (lymphomas can be the leading point), lymphoma, stricture. Mesenteric defects can occur with marathon runners. If its caused by cancer, its usually metastasis (colonic, ovarian, pancreatic, gastric).

Nausea/Vomiting, abdominal distension. Dehydration due to decreased oral intake and decreased body uptake. Can get ischemic bowel from distention and increased intraluminal pressures causing ischemia.

Episodic pain, usually for a few minutes intermittently, though can be constant. The earlier and more sever the vomiting, the more proximal the obstruction. Complete obstruction causes inability to pass bowel movement or flatus, though partial bowel obstruction often associated with passage of stool and flatus. Mechanical obstruction early has high-pitched bowel sounds where as later in the course and in adynamic ileus will have diminished or absent bowel sounds.

Only need upright chest and abdominal X-ray. Can help confirm suspicion for obstruction, severe constipation, or free air. Will show multiple air-fluid levels (string of pearls, air-fluid levels, step-laddering). Looking for dilation > 2.5cm and presences of air-fluid levels differing > 5mm from each other. Sensitivity 80%, specificity 67-80%. Does not show point of twisting.

CT scan is the diagnostic method of choice. Look for: bowel wall thickening > 3mm, submucosal edema, ascites, ‘target sign’ – alternating hypo/hyperdense layers indicating intussesception, ‘whirl sign’ from rotating small bowel mesentery from volvulus, ‘venous cut-off sign’ due to thrombosis. Finding transition point does not appear to make difference in emergent vs delay and sometimes has been off from intraoperative findings. No oral contrast: ACR recommends against it, Rating 9.

Abdominal US: More sensitive and specific than plain films for SBO. In one study, US was 75% sensitive (Suri, 1999). Ultrasound Podcast Video Tutorial. Jang, 2010 study: 10min teaching residents, found US to be 91% sensitive. Look for dilated loops of bowel in several quadrants (>2.5cm), looked for back and forth peristalsis.

With significantly elevated leukocytosis, consider bowel gangrene, abscess, or peritonitis. Also should check lactate for signs of ischemia as well.

Treatment: Closed-loop obstruction, bowel necrosis, and cecal volvulus usually require preoperative broad-spectrum antibiotics (Zosyn 3.375g / Unasyn 3g q6h). True mechanical obstruction requires surgery.

NG tube: not necessarily unless presence of severe distention or vomiting.

Large Bowel Obstruction

Causes: carcinoma (MCC, adenocarcinoma of the colon or rectum), fecal impaction, ulcerative colitis, volvulus (usually elderly, bedridden, psychiatric patients on anticholingerics or hx/o constipation), diverticulitis, intussuspection, pseudo-obstruction.

Hypogastric. Usually more constipation and gross distention.

Sigmoid Volvulus

Causes 5-6% of large bowel obstructions. Most often in inactive elderly, severe psychiatric or neurologic diseases. Usually due to severe constipation. Due to bowel segment twisting on mesenteric axis leading to luminal obstruction. Mortality 20% overall. Cecal volvulus is any age, commonly younger people, high mortality.

One of the few diagnosis that can be made on plain films (80% of the time), severely dilated single loop of colon in left abdomen, both ends in pelvis and bowel pointing superiorly (bent inner tube sign). Also can do barium enema which will show ‘bird’s beak’ deformity at point of twists, cut-off of contrast flow into proximal colon.

Treatment: Surgery for gangrenous bowel, usually can be reduced with sigmoidoscopy and rectal tube insertion (successful 85-95%), recurrence rate is 90% if reduction is not followed by colopexy

Adynamic Ileus

Occurs to some degree after most open abdominal operations. Other causes: peritonitis, trauma, ischemia, medications (opiates and anticholingerics), electrolyte disorders (hypokalemia). To differentiate SBO vs ileus in post-op patient, SBO usually have return of BMs prior to have symptoms where as ileus do not.

Treatment: conservative management including IV fluids and observation.


Ogilvie syndrome: mimics bowel obstruction, usually lower colonic obstruction. Very large dilated haustra in large intestines with little fluid/stool. RF: elderly, anticholingerics and TCAs. Colonoscopy is the treatment for decompression. Neostigmine infusion for refractory cases.

Clinical Cases

Radiopedia.org, String of Beads sign

Radiopedia.org, Small bowel obstruction on X-ray 


Tintinalli, Seventh Edition, Chapter 86: Bowel Obstruction and Volvulus

Crashing Patient, Scott Weingart, Large Intestine, Reviewed 4/14/14

Crashing Patient, Scott Weingart, Small Intestine, Reviewed 4/14/14

UptoDate, Epidemiology, clinical features, and diagnosis of mechanical small bowel obstruction in adults, Reviewed 4/14/14

Ultrasound Podcast, Episode 36 – Small Bowel Obstruction

American College of Radiology Appropriateness Criteria, Revised 2013

The Short Coat Blog, Lauren Westafer, Small Bowel Obstruction – A Likely Story?

A Life at Risk blog, Bowel Obstruction and physical examination

086. Bowel Obstruction and Volvulus

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