NEJM: Low-dose CT is exam of choice for appendicitis eval

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Low-dose CT proved noninferior to standard CT in terms of negative appendectomy rates among young adults presenting with suspected appendicitis, according to a study published April 26 in the New England Journal of Medicine.

While CT has emerged as the diagnostic exam of choice for evaluation of patients with suspected appendicitis, concerns about radiation exposure have increased in recent years. In the U.S., more than 250,000 appendectomies are performed annually. Many of these patients, and many more with suspected appendicitis, undergo CT. “Such a large number of exposures may ultimately have an effect on the incidence of cancer in these populations, although the individual risk for cancer is extremely low,” wrote Kyuseok Kim, MD, of the department of emergency medicine at Seoul National University College of Medicine, and colleagues.

Exploratory studies have suggested dose reductions in the 50 to 80 percent range do not interfere with the diagnosis of appendicitis. However, such protocols have not gained acceptance because of concerns about potentially inferior image quality with low-dose studies.

Kim and colleagues devised a randomized study to assess the role of low-dose CT in the evaluation of appendicitis among young adults.

The study population included 891 patients ages 15 to 44 who were randomly assigned to low-dose or standard CT from September 2009 through January 2011. The primary endpoint was the rate of negative appendectomy. The researchers also analyzed secondary endpoints, including the rate of appendiceal perforation, the proportion of patients who required additional imaging exams and diagnostic confidence.

The CT protocols aimed at effective doses of 2 mSv in the low-dose group and 8 mSv in the standard-dose group. Among the 444 patients in the low-dose group, the median dose-length product was 116 mGy cm. Among the 447 patients in the standard-dose group, the median dose-length product was 521 mGy cm.

The negative appendectomy rates were 3.5 percent in the low-dose group and 3.2 percent in the standard-dose group, which established the noninferiority of low-dose CT to standard CT. Appendiceal perforation rates were 26.5 percent and 23.3 percent, respectively, in the low-dose and standard groups.  

However, patients in the low-dose group were more likely to require additional imaging, 3.2 percent vs. 1.6 percent in the standard group; and they had a longer interval between the CT study and surgery. Kim et al hypothesized that these differences may have been due to clinicians’ hesitations to base operative decisions on low-dose imaging data.

The researchers attributed the comparable performance of low-dose CT to the imaging capability of current-generation CT systems and the simplicity of CT interpretation in the diagnosis of appendicitis. Kim et al noted that these factors may offset any loss of image quality associated with low-dose exams.

“Our findings corroborate those of previous exploratory studies that support a reduction in the radiation dose when CT is used in the diagnosis of appendicitis,” concluded Kim and colleagues. They suggested use of low-dose CT as the first-line imaging test, explaining that it provides comparable clinical outcomes and diagnostic performance when paired with selective additional imaging and clinical observation.