CT safely rules out acute appendicitis

The incidence of unnecessary appendectomies has declined with the rise of abdominal CT scanning. Clinical evidence now shows specific CT findings can safely exclude acute appendicitis, according to a study in the October issue of the American Journal of Roentgenology.

Dr. Paul Nikolaidis, an assistant professor at Northwestern University, and colleagues from Northwestern and the Hospital of the University of Pennsylvania retrospectively evaluated 366 consecutive patients who presented at their respective institutions with lower abdominal or right lower quadrant pain. Patients underwent contrast-enhanced CT scanning to confirm or rule out acute appendicitis.

The investigators found they could safely exclude the condition when neither the appendix nor secondary signs of acute appendicitis were visible on CT.

One experienced abdominal radiologist and one staff radiologist reviewed CT scans. CT could not visualize the appendix in 13% of patients but found the cause for patient's symptoms in 26% of cases. Twenty-four patients were given an alternate diagnosis with follow-up imaging or clinical evaluation. Only one patient with a nonvisible appendix had acute appendicitis.

The scanning protocol included axial CT scans from the diaphragm to the symphysis pubis using 5-mm slices at 5-mm intervals with a rotation speed of 0.8 sec, table speed of 15 mm per rotation cycle, high-speed pitch (6:1), 120 kVp, and variable 190 to 230 mAs, depending on habitus.

The absence of a distinctly visualized appendix and any secondary signs of acute appendicitis - abscess formation, localized perforation, periappendiceal fat stranding, or appendicolith - reduces the chances of acute appendicitis, according to the investigators. The amount of fat surrounding the cecum influences the ability to visualize the appendix and helps secure diagnosis.

For surgeons, steering between the decrease in unnecessary appendectomy rates and the need to make a diagnosis before perforation occurs is a fine balancing act. The risk of appendiceal perforation and postoperative complication rates can both skyrocket because of misdiagnosis. Surgeons have thus far considered 20% as an acceptable unnecessary appendectomy rate to minimize perforation's risks, morbidity, and mortality.

CT has boosted diagnostic accuracy for acute appendicitis from 93% to 98%, resulting in lower unnecessary appendectomy rates without a proportionate increase in perforation risks, the researchers said.

For more information from the Diagnostic Imaging archives:

FDA okays radiolabeled agent to image appendicitis

Spiral CT proves superior for diagnosing appendicitis

Ultrasound's potential expands in abdomen

Emergency department tackles cases of suspected appendicitis

CT gains popularity for diagnosing appendicitis in children