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Small Bowel Obstruction: Causes and Imaging Techniques

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Small bowel obstruction can be detected by different imaging techniques. This article describes the radiological findings of small bowel obstruction.

Written by

Dr. Narmatha. A

Medically reviewed by

Dr. Varun Chaudhry

Published At October 5, 2022
Reviewed AtJune 27, 2023

Introduction:

Small bowel obstruction is the blockage of the small intestine. Small bowel (intestine) obstruction can be either congenital or mechanical. Small bowel obstruction is most commonly caused by adhesions after intestine surgery. Radiological imaging of the small intestine is helpful in the detection of location, cause, and degree of obstruction. The radiological investigation is useful when the clinical examination and laboratory findings are unreliable in the detection of small bowel obstruction. They can determine whether the obstruction needs laparotomy (surgical procedure performed through the abdominal wall) or nonsurgical management.

What Are the Causes of Small Bowel Obstruction?

Congenital:

  • Jejunal atresia (a condition that causes complete obstruction of the proximal aspect of the small intestine in newborns).

  • Ileal atresia or stenosis (a condition in which narrowing or blockage of the part of the ileum).

  • Enteric duplication cyst (a fluid-filled sac found in the gastrointestinal tract during birth).

  • Midgut volvulus (a condition in which the intestine becomes twisted and results in bowel obstruction).

  • A mesenteric cyst (a fluid-filled sac in any part of the mesentery [a membrane that connects the intestine to the posterior abdominal wall]).

  • Meckel diverticulum (a congenital condition in which failure in the vitelline duct's obliteration results in the small pouch's formation at the small intestine's lower part).

Mechanical:

  • Hernias (bulging out of organs or fatty tissues through a weak part of the muscles or tissue) - Femoral and inguinal hernias are the most common cause of small bowel obstruction.

  • Intussusception (a condition in which part of the intestine telescopes or slides into a nearby part of the intestine).

  • Tumor.

  • Crohn's disease (chronic inflammatory bowel disease).

  • Gallstones.

  • Foreign bodies.

  • Fibrous adhesions from prior surgery (formation of fibrous tissue or scar in the intestine after an intestine surgery).

  • Radiation enteritis (swelling of the lining of the small intestine induced by radiation).

  • Intestinal ischemia (a condition that stops the blood flow to the intestine and causes thickening of the small bowel wall).

  • Gallstone ileus (gallstone obstructs the lumen of the small intestine bypassing through cholecysto-enteric fistula).

  • Meconium ileus (a condition in which stool becomes thick and sticky that causes intestinal obstruction in children).

What Are the Imaging Techniques Used in the Diagnosis of Small Bowel Obstruction?

Small bowel obstruction can be diagnosed with the help of the following imaging techniques. They are -

  1. Abdominal radiograph.

  2. Ultrasound.

  3. Computed tomography (CT).

  4. Barium follow-through and enteroclysis.

1. Abdominal Radiograph:

The abdominal radiograph is the first choice of imaging technique advised when the patient is suspected of having a small bowel obstruction. In small bowel obstruction, the abdominal radiograph shows the following radiological findings:

  • Dilatation of small bowel loops proximal to the bowel obstruction (dilatation greater than 2.5 to 3 cm).

  • The string of pearl signs - A sign of small bowel obstruction in which tiny gas bubbles are found over the superior wall of the small intestine and trapped between the folds of the small intestine [valvulae conniventes]. The lower margin of the bubbles has an oval appearance.

  • Thickened bowel walls.

  • Strangulation - A condition in which blood supply to the hernia is reduced, which appears like any of the following signs in radiograph:

  • Presence of gas in the portal vein.

  • Pneumatosis intestinalis (presence of free air within the walls of the intestine).

  • Edematous folds (swelling of the intestinal folds).

  • As abdominal radiograph shows only high-grade obstruction, additional images are advised.

2. Ultrasound:

Ultrasound shows the following radiological findings in small bowel obstruction.

  • Ineffective peristalsis (muscular contraction of the digestive tract).

  • Multiple dilated bowel loops greater than 3 cm.

  • Fluid-filled loops of the small intestine.

  • Obstruction by tumor (cancer) or hernia is visible.

  • Bowel wall perfusion might be visual in Doppler ultrasound.

  • Pneumatosis intestinalis.

  • Prominent valvulae conniventes (folds of the small intestine).

3. Computed Tomography (CT):

Computed tomography shows the following radiology findings in small bowel obstruction.

  • Noncontrast CT.

  • Small bowel feces sign - The presence of fecal-like material inside the dilated lumen of the small intestine in small bowel obstruction.

  • Dilated small bowel loops greater than 2.5 cm.

  • Distally collapsed loops.

  • Whirl sign - When the small intestine twists around the mesentery, it causes compression of the small bowel lumen and blood vessels of the bowel wall. It is also called the whirlpool sign.

  • The string of pearl signs.

  • Beak sign - Tapered obstruction of the intestine resembles the bird's beak.

  • Computed tomography has 81- 94 percent sensitivity and 96 percent specificity for diagnosing high-grade obstruction. But their sensitivity and specificity decrease respectively by 64 and 79 percent when considering all grades of obstruction.

  • CT is not an ideal imaging technique for a low-grade or subacute small bowel obstruction.

  • Contrast-enhanced CT for intestinal ischemia has a sensitivity of more than 90 percent.

  • Contrast CT.

Contrast-enhanced CT shows the following signs of small intestine obstruction:

  • Thickened bowel wall.

  • Ascites (collection of fluid in the abdominal cavity).

  • Pneumatosis intestinalis and gas in mesenteric or portal veins.

  • Whirl sign.

  • Tortuous engorged (enlarged) mesenteric vessels.

  • Mesenteric hemorrhage (loss of blood from the ruptured mesenteric blood vessels).

  • CT enteroclysis.

When CT is unreliable in diagnosing small bowel obstruction, CT enteroclysis is used. CT enteroclysis is a new diagnostic tool that uses an enteroclysis tube for contrast administration to visualize the obstruction. It has 89 percent sensitivity and 100 percent specificity for diagnosing small bowel obstruction.

4. Barium Follow-Through and Enteroclysis:

Enteroclysis is the use of an enteroclysis tube to administer oral contrast into the intestine and bypass the stomach. Because of nausea and vomiting in acute bowel obstruction, patients have poor tolerance to oral contrast. In addition, water-soluble contrast (special dye) materials may be diluted in the extended fluid-filled bowel; thus, the degree of opacification becomes insufficient. The barium enema is helpful for the detection of distal colon obstruction. It may show the following radiological findings in small bowel obstruction:

  • Snakehead appearance - In small bowel obstruction, there is a bulbous appearance proximal to the obstruction resulting from peristaltic movement.

  • Beak sign.

  • Dilated loops of the small bowel.

  • It can detect only low-grade and intermittent bowel obstruction.

Conclusion:

Abdominal radiography is the initial radiograph recommended for the diagnosis of small bowel obstruction. An abdominal radiograph is readily available and economical. It has 71 percent sensitivity for high-grade small bowel obstruction. The sensitivity of ultrasound is more than abdominal radiographs by 89 percent in detecting small bowel obstruction. Computed tomography has increased sensitivity (81 to 94 percent) compared to abdominal radiographs in detecting high-grade small bowel obstruction. CT can determine the cause of obstruction and differentiate bowel obstruction from the ileus.

Frequently Asked Questions

1.

What Symptoms Are Presented by Small Bowel Obstruction?

The symptoms of small bowel obstruction are as follows:
- Nausea.
- Bloating.
- Vomiting.
- Severe constipation.
- Dehydration.
- Malaise
- Abdominal pain and cramps.
- Lack of appetite.

2.

How Is Small Bowel Obstruction Treated?

Small bowel obstruction is treated by giving intravenous fluids to a person and NPO (nothing by mouth) for bowel rest. In addition, the patient is given antiemetic medications to treat vomiting and nausea, and a nasogastric tube is used for bowel decompression. Sometimes, a surgical method is also used to treat bowel obstruction when small intestines get blocked completely.

3.

How Severe Is Small Bowel Obstruction?

Small bowel obstruction is a life-threatening condition as it can cause damage or death of the bowel tissues. Trapped bowel causes an accumulation of fluids, air, and food in the small intestine. Bowel obstruction can also affect the blood supply, and if the condition is not treated timely, it can lead to kidney failure and severe dehydration.

4.

How Long Can a Person Live With Small Bowel Obstruction?

Small bowel obstruction usually occurs in older people and is treated differently than other medical conditions causing bowel obstruction. However, the patients show a very poor prognosis for small bowel obstruction, irrespective of age. The mortality rate decreases if the surgery is done in the initial few hours, but if left untreated, the condition can lead to 100 percent death of a person.

5.

When Do We Need Surgery for Small Bowel Obstruction?

 
Surgical treatment for small bowel obstruction is recommended when the conventional methods are no longer effective. Non-operative procedures are mainly helpful in treating partial intestinal obstructions. Therefore, surgical interventions are needed to resolve a person's complete small bowel obstruction condition.

6.

Can Bowel Obstruction Be Treated Without Surgery?

Bowel obstruction is a very dangerous and painful condition, and a person requires hospital admission for proper care.  However, the patient does not always require surgery to treat intestinal obstruction as it can resolve itself. The patient also does not have any reoccurrence of the condition in the future.

7.

How Do Doctors Clear Bowel Obstruction?

The doctor clears the bowel obstruction through surgery and removes the damaged or dead section of the intestine. In addition, the doctor may also advise sick people to use a metal stent for self-expanding obstruction, who cannot undergo surgery. Also, enemas of fluid or air are used to increase the pressure inside the bowel to clear the block.

8.

Can Colonoscopy Help In Detecting Small Bowel Obstruction?

Small bowel obstruction can be detected with ultrasound, computed tomography (CT scans), abdominal radiographs, and barium-follow through and enteroclysis. Among all these diagnostic tools, computed tomography is the most preferred method to detect small bowel obstruction. Colonoscopy is mainly used for detecting bowel obstruction in the large intestines.

9.

Is Small Bowel Obstruction an Emergency Condition?

 
Small bowel obstruction is considered an emergency medical condition requiring immediate surgery as it can cause high morbidity. Most cases of small bowel obstruction are caused due to adhesion occurring from any past surgeries. However, the condition can also arise in a person with no previous surgery history.

10.

Which Food items Can Cause Bowel Obstruction?

The food items that can cause bowel obstruction are as follows:
- Vegetables include cauliflower, broccoli, beets, spinach, sprouts, carrots, peas, onion, and turnips.
- Fruits such as grapes, bananas, apples, melons, and resins.
- Dry fruits.
- Coconut.
- Apricots.
- Meat products.

11.

What Is the Survival Rate of People Having Bowel Obstruction Surgery?

Bowel obstruction surgery decreases the mortality rate to almost eight percent if performed during the first 36 hours of obstruction. However, if the treatment is delayed beyond 36 hours, the mortality rate is only 25 percent. Therefore, the overall prognosis of bowel obstruction is very poor in most cases.

12.

Should a Person Eat if They Have a Bowel Obstruction?

A person having bowel obstruction should avoid taking large meals in a day. Instead, the doctor recommends a person take five to six small meals throughout the day cut into very small pieces. Also, a person is advised to take a more liquid diet and low-fiber meals and avoid meat and cereals, as they are tough to digest.

13.

Which Antibiotics Are Used for Bowel Obstruction?

The doctor usually prescribes Metronidazole antibiotics to a person suffering from a small bowel obstruction. The antibiotic protects the person against bacteremia and bacterial translocation during bowel obstruction.

14.

Is Oatmeal a Good Option for Small Bowel Obstruction?

Oatmeal is suitable for small bowel obstruction as it contains soluble fiber that relieves intestinal blockage. However, people not used to eating oatmeal can suffer constipation or other digestive issues.
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Dr. Varun Chaudhry

Radiodiagnosis

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