CT imaging informed an alternate diagnosis in nearly one-third of adults presenting with suspected acute appendicitis, according to a study published Oct. 2 in Radiology. 

Clinical diagnosis of appendicitis can be challenging, evidenced by a negative appendectomy rate in the 20 percent range prior to widespread use of CT. Deployment of CT has dropped this rate to less than 10 percent. Nonfocused abdominal CT also provides an opportunity to diagnose other acute disease processes with symptoms that mimic appendicitis and may be difficult to diagnose on clinical grounds. However, data examining this connection are sparse.

Thus, B. Dustin Pooler, MD, of the department of radiology at the University of Wisconsin School of Medicine and Public Health in Madison, and colleagues conducted a retrospective study to assess alternative diagnoses in adults undergoing CT for suspected acute appendicitis.

Pooler and colleagues reviewed the records of 1,571 consecutive adults who underwent CT imaging for evaluation of suspected appendicitis from January 2006 to December 2009. In addition to recording the initial diagnosis at CT, the researchers followed the clinical course of all patients for a minimum of 12 months to identify delayed diagnoses and interventions.

Appendicitis was diagnosed in 23.6 percent of patients, and an alternative diagnoses was made at CT in 31.6 percent of patients. In 44.8 percent of patients, a specific diagnosis was not made on the basis of CT imaging.

The most common broad categories of alternate diagnoses included nonappendiceal gastrointestinal conditions, gynecologic conditions, genitourinary conditions and hepatopancreaticobiliary conditions. Approximately half of the patients who received an alternate diagnosis were hospitalized and one in four underwent surgery or an invasive procedure. These rates were much higher than those of patients who did not receive a specific diagnosis, which suggests “that lack of a specific diagnosis at CT largely excludes important conditions that may require immediate invasive therapy.”

Among patients who received a specific alternate diagnosis at CT, 81.9 percent also received a specific clinical diagnosis. The diagnoses were concordant in 94.3 percent of cases. Among patients who did not receive a specific diagnosis on the basis of CT, 82.7 percent also did not receive a clinical diagnosis.

“These results offer strong support for the triage role that nonfocused abdominopelvic CT plays in rapidly narrowing the focus in an urgent presentation fraught with insensitive and nonspecific clinical findings,” wrote Pooler et al.

The researchers recommended use of a nonfocused CT protocol rather than a focused protocol for evaluation of suspected appendicitis. Although radiation exposure may be higher with the nonfocused protocol, it provides the benefit of enabling a wide array of alternative diagnoses. Similarly, ultrasound, a nonionizing option sometimes used in the diagnosis of appendicitis in specific populations, is limited in its ability to inform many alternate diagnoses.

Pooler and colleagues noted that 17.3 percent of patients who did not receive a specific diagnosis at CT received a specific clinical diagnosis. Often these were conditions that lacked specific findings at CT.

“Our findings show that, in cases of clinically suspected acute appendicitis, nonfocused abdominopelvic CT can efficiently and reliably identify a wide range of alternative causes for symptoms, in addition to confirming or ruling out appendicitis,” concluded Pooler et al.