MSCT helps brings negative appendectomy rate to historic low

Multislice CT has helped Massachusetts General Hospital reduce the number of unnecessary appendectomies performed there almost sevenfold in the last decade, according to a study in the June issue of the American Journal of Roentgenology.

Until the late 1990s, nearly 20% of appendectomies in the U.S. proved negative. The figure satisfied physicians weighing the surgery's risks against those of a perforated appendix. Selective use of CT to diagnosis appendicitis, however, brought that rate at MGH down to 7% in 2001. The rate has since continued to drop.

Dr. James T. Rhea and colleagues at MGH retrospectively reviewed the records of 753 patients with suspected appendicitis between 2001 and 2003. Among these patients, 663 underwent imaging with a four-slice CT scanner.

The negative appendectomy rates for patients with and without CT exams were 3% and 5.6%, respectively.

Patients who underwent MSCT scanning showed a 39% incidence of appendicitis. The modality provided a sensitivity and specificity of 99% and 95%, respectively. The overall rate of equivocal CT interpretations was 3.3%.

Radiologists and surgeons agreed upon a selective use of CT to image patients suspected of acute appendicitis. They based their criteria on classic signs, symptoms, and lab findings. Pediatric surgeons used a higher benchmark to limit their patients' radiation exposure.

Investigators found the negative appendectomy rate for female pediatric patients undergoing MSCT was better than for patients overall undergoing MSCT. The difference was statistically significant (all patients, p = 0.326; female pediatric patients, p = 0.03).

The imaging protocol included:

• 2.5-mm slice thickness

• 2.5-mm image reconstruction interval

• 15-mm/rotation table speed

• 40 mL of colon contrast agent per 1000 mL of saline solution via a small pediatric rectal catheter for adult and pediatric patients

• nonionic IV contrast

• oral contrast

MGH surgeons selected approximately 12% of patients with suspected appendicitis for surgery without CT. The researchers found no statistically significant difference in the negative appendectomy rates between patients sent for CT and those whose clinical and lab findings were deemed sufficient to authorize surgery without CT.

Although CT should be used in most patients with suspicious signs of appendix disease, findings suggest that clinicians are limiting CT to the proper surgical candidates, the investigators noted in the study.

For more information from the Diagnostic Imaging archives:

CT during pregnancy proves necessary in some situations

Multislice CT refines acute appendicitis diagnosis

Spiral CT proves superior for diagnosing appendicitis