Until now, plain abdominal radiography is still used to help diagnose cases of small bowel obstruction (SBO). Despite limited sensitivity and specificity, plain abdominal radiography is still widely used because this method is inexpensive, available in most health facilities, and easy to use. Additionally, plain abdominal radiography can monitor disease progression. So, plain abdominal radiography is necessary to evaluate small bowel obstruction diagnosis.

Plain Abdominal Radiography in Diagnosing Small Bowel Obstruction
Plain Abdominal Radiography of Small Bowel Obstruction
Image source: http://www.svuhradiology.ie


Overview of Small Bowel Obstruction

What are the causes of small bowel obstruction?

The most common causes of small bowel obstruction are intestinal adhesions, neoplasms, and strangulated hernias. And other SOB causes are inflammatory bowel disease, intussusception, volvulus, fistula, cholelithiasis, collection of parasites, and food boluses.


What are Clinical Manifestations of Small Bowel Obstruction?

Patients' main complaints with small bowel obstruction are obstipation, nausea to vomiting, intermittent abdominal muscle stiffness, and appetite loss. The abdominal physical examination may reveal abdominal distension. For the definite diagnosis, the abdominal imaging investigations reveal an image of the air-fluid level, string of pearls, and distal bowel dilatation.


Plain Abdominal Radiography in Small Bowel Obstruction

Sensitivity and Specificity 

The 2017 study, involving 216 patients in the emergency department, aimed to evaluate plain abdominal radiography's ability to detect small bowel obstruction and small bowel ileus. The study results indicated that plain abdominal radiography had sensitivity and specificity in detecting small bowel obstruction by 82% and 92.4%.


Advantages and Imaging

The plain abdominal radiographs can provide signs to confirm a suspected diagnosis of small bowel obstruction. Plain radiographs of the abdomen in small bowel obstruction include:
  • The collapsed and dilated small intestine with a size of more than 3 cm.
  • There are more than two water fluid levels.
  • A string of pearls occurs because the amount of gas retained in the small intestine remains less than the fluid amount.

Disadvantages 

Some of the plain abdominal radiography's disadvantages in detecting small bowel obstruction are as follows:
  • Cannot diagnose the cause in most cases of small bowel obstruction
  • Not able to detect any complications due to the ischemic process
  • There may be errors in detecting small bowel obstruction, especially if it is mild.
  • Difficulty differentiating small bowel obstruction from paralytic ileus conditions
  • Difficulty identifying the degree of obstruction if it occurs in the ileocaecal area



Abdominal CT Scan Examination in Small Bowel Obstruction

The abdominal CT scan is the preferred radiological examination to confirm and evaluate intestinal obstruction cases, both small and large intestine. This method has a sensitivity of approximately 90–96% in detecting acute severe small bowel obstruction, with a specificity of approximately 96–100%.

CT scan is a useful radiological investigation for the following conditions:
  • In emergency cases, a CT scan will detect several signs that indicate the patient needs surgery.
  • On plain abdominal radiographs where there is no clear picture of small bowel obstruction, CT scan can exclude cases of pseudo-obstruction
  • CT scan can identify the cause of small bowel obstruction (sensitivity 73–95%)
  • CT scans can identify other causes of abdominal pain besides small bowel obstruction.
  • CT scan can confirm the presence of ischemia or perforation of the small intestine.


The limitations of CT scans are a low sensitivity (about 50%) for detecting low-grade small bowel obstruction and the location of low-grade small bowel obstruction. Additionally, exposure to ionizing radiation is more dangerous for the patient. CT scan with contrast method may be contraindicated in patients with allergies or kidney disorders.


Conclusion

The accuracy of plain abdominal radiography is almost the same as the abdominal CT scan as a supporting investigation in small bowel obstruction cases. Cheap and easy to be performed in all hospitals, make plain abdominal radiographs mandatory in the emergency department when handling small bowel obstruction cases.

Performing Plain Abdominal Radiography can repeatedly be. Therefore, by using this examination, doctors can monitor the disease's progress and decide the necessary actions.

CT-scan use is necessary in cases where plain abdominal radiography cannot clearly identify small bowel obstruction and confirm the presence of small bowel ischemia or perforation.

However, in non-traumatic abdominal pain cases with unclear clinical symptoms, the abdominal CT scan has the advantage of diagnosing small bowel obstruction and other differential diagnoses, such as appendicitis, pancreatitis, urolithiasis, and diverticulitis.


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