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Small Bowel Obstruction: Diagnosis

Signs, Symptoms, Labs, and Imaging Findings

Jul 12, 2009 David Henry

Small bowel obstruction is a serious intestinal disorder that requires surgery if it does not resolve. Diagnosis and imaging will be discussed here.

This article is Part 2 of the three-part series on small bowel obstruction. Part 1 describes the anatomy of the intestinal tract and lists the most common causes of small bowel obstruction. Below, the signs, symptoms, diagnosis, lab findings, and imaging tests are discussed. In Part 3, the treatment options and prognosis are discussed.

Signs, Symptoms, and Diagnosis of Small Bowel Obstruction

When the small intestinal lumen (opening in the center) becomes narrowed or obstructed, gas, secretions, and food become backed up proximal to (before) this obstruction. This causes dilation of the bowel proximal to the obstruction. This can cause nausea, vomiting, and intermittent, crampy abdominal pain. The abdomen can also appear distended. Since stool cannot pass into the colon, the patient is unable to defecate regularly and complains of constipation. The patient may have a history of abdominal surgery (causes adhesions) or may have a hernia, inflammatory bowel disease, or gallstones (see "Causes of Small Bowel Obstruction" in the previous article).

Vomiting may cause the patient to become dehydrated. He may have a fever, an elevated white blood cell count, tachycardia (heart rate over 100), and hyperactive, high-pitched bowel sounds. These bowel sounds are caused by the intestines trying to push intestinal contents past the obstruction.

Laboratory Findings in Small Bowel Obstruction

Since the patient may have vomited a great deal and lost a lot of water, the blood may be more concentrated ("hemoconcentration" occurs when there is less water in the blood). This can cause the hematocrit level to be higher. Since the patient vomits up hydrochloric acid from the stomach, this loss of acid causes the blood to become more basic (alkalotic). The specific derangement in small bowel obstruction is termed "hypochloric (low chloride) metabolic alkalosis (more basic)."

Imaging Findings in Small Bowel Obstruction

The first imaging test done in suspected small bowel obstruction is often the "abdominal series," which consists of a supine (laying down on one's back) abdominal X-ray, an upright (standing) abdominal X-ray, and an upright chest X-ray. Air seen underneath the diaphragm (usually on the right side above the liver) on an upright X-ray means that there is "free air" within the abdominal cavity. This is abnormal and often means that the stomach or intestines has a hole (perforation) in it. This can occur in severe, "strangulating" small bowel obstruction in which part of the bowel wall loses its blood supply and necroses or dies.

X-ray: 3 findings in small bowel obstruction include: Dilated loops of small bowel, air-fluid levels proximal to (before) the obstruction, and little air in the colon (large intestine) since the air can't get past the obstruction.

Barium enema

Upper GI series with small bowel follow-through

CT scan: A very sensitive (80-90%) and specific (70-90%) test in the diagnosis of small bowel obstruction. A CT scan can show exactly where the obstruction is located, since the small bowel will be dilated before the obstruction and decompressed (smaller) after the obstruction. It can also help to identify the cause of the obstruction (tumor, hematoma, hernia, etc.)

Link to Small Bowel Obstruction: Anatomy of the Digestive Tract and Causes of Small Bowel Obstruction

Reference

Chapter 27: Small intestine. Brunicardi FC, et al., Eds. Schwartz's Principles of Surgery. McGraw-Hill, 2004. *One of the classic textbooks in general surgery.

The copyright of the article Small Bowel Obstruction: Diagnosis in General Medicine is owned by David Henry. Permission to republish Small Bowel Obstruction: Diagnosis in print or online must be granted by the author in writing.

Dilated small bowel loops (indicate obstruction)