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Reducing radiation exposure with CT scans

Robin Wulffson MD's picture
appendicitis, perforated appendix, CT scan, wrong diagnosis

Computed tomography (CT) is an excellent diagnostic tool for many medical conditions including acute appendicitis. The down side of its use is the exposure of the patient to a significant amount of ionizing radiation. In children and young adults, exposure to CT radiation is of particular concern because it increases the risk of developing a malignancy in later life.

Another problem with any diagnostic procedure is either a false negative or false positive result. A false negative diagnosis delays treatment for a condition; thus, allowing it to worsen. For example, a false negative diagnosis of appendicitis increases the risk of a ruptured appendix and peritonitis (a serious abdominal infection, which has a significant mortality rate). Conversely, a false positive diagnosis exposes the patient to unnecessary surgery. To assess this problem, Korean researchers at Seoul National University Bundang Hospital set out to evaluate the diagnostic accuracy of a low-dose CT scan versus a standard-dose CT scan in young adults with suspected appendicitis. Their findings were published in the April 26 issue of The New England Journal of Medicine.

The study group was comprised of 891 patients (aged 15 - 44 years) who presented at the hospital’s emergency department with abdominal pain and other symptoms suggestive of appendicitis. Patients with low body mass (thin patients). The researchers randomly assigned 891 patients with suspected appendicitis to either a low-dose CT scan (444 patients) or a standard-dose CT scan (447 patients). The median radiation dose was 116 mGy•cm in the low-dose group and 521 mGy•cm in the standard-dose group, meaning that the low-dose group received 22% of the radiation dosage that the standard-dose group. The primary end point of the study was the percentage of negative appendectomies among all appendectomies. Secondary end points included the appendiceal perforation rate and the proportion of patients with suspected appendicitis who required additional diagnostic imaging procedures.

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The researchers reported a false negative rate of 3.5% (6 of 172 patients) in the low-dose CT group and 3.2% (6 of 186 patients) in the standard-dose CT group (difference, 0.3 percentage points. The two groups did not differ significantly in terms of the appendiceal perforation rate (low-dose CT: 26.5%; standard-dose CT: 23.3) or the proportion of patients who needed additional imaging procedures (low-dose CT: 3.2% ; standard-dose CT: 1.6%).

The authors concluded that a low-dose CT scan was not inferior to a standard-dose CT scan in regard to false negative rates among young adults with suspected appendicitis.

Appendicitis is one of the most common causes of emergency abdominal surgery in the United States. It usually occurs when the appendix becomes blocked by feces, a foreign object, or rarely, a tumor. The symptoms of appendicitis vary. It can be difficult to diagnose the disease in young children, the elderly, and women of childbearing age. Typically, the first symptom is pain around the navel (belly button). The pain may be vague at first; however, it later becomes increasingly sharp and severe. The patient may experience reduced appetite, nausea, vomiting, and a low-grade fever.

Reference: The New England Journal of Medicine