Improving the Role of CT in Diagnosing Perforated Appendicitis: Can Appendiceal Air Help?

Abstract

Appendectomy is one of the most commonly performed surgical procedures, and imaging plays a key role in guiding the decision whether to operate, what surgical approach to use, or whether to defer surgery and treat the patient medically. Despite a robust literature, diagnosis of appendicitis remains controversial, especially for patients with atypical presentations that are commonly misdiagnosed resulting in increased morbidity and potential litigation (1). The goal for all patients is to minimize unnecessary surgery (the negative appendectomy rate) and cost-effectively treat positive appendicitis patients with minimum morbidity. This isevenmoreimportantinpregnantwomen,inwhomthenegative appendectomy rate has been as high as 54% (2). Overall, the mean negative appendectomy rate of 26% decreases to 6%–10% when imaging is performed (3–5). Computedtomography(CT)evaluationofsuspectedappendicitis (6,7) is routine except in children and young women where ultrasound (which is highly operator dependent) or magnetic resonance imaging, respectively, may be the initial diagnostic test (8–10). Yet indiscriminate use of CT may lead to a longer time to operation with an increased rate of appendiceal perforation (11). Therefore, the triage of patients to CT should be done carefully. Perforated appendicitis is associated with a greater morbidity. Prompt recognition of appendiceal perforation on CT is important to avoid unnecessary delay in performing indicated surgery. Azok et al (12) introduced a new sign to assist the CT diagnosis of appendiceal perforation, namely intraluminal appendiceal air specifically within an obstructed portion of the appendix (12). Although older reports found conflicting results and thus the sign of appendiceal air has not been advocated, in this new report a more specific analysis looked as the subset of patients with CT signs of definite appendicitis (eg, dilated appendix, thick appendiceal wall, periappendiceal fat stranding) but without signs of perforation (periappendiceal phlegmon, abscess, extraluminal gas, extraluminal appendicolith or focal wall defect). Using surgical and pathological finding to define truth, the authors found that imaging-occult necrosis or perforation was present in 17.4% (65/374) and that intraluminal air and appendicolith were predictive variables that yielded odds ratios of 2.64 and 2.67, respectively. Increasing patient age also was predictive (odds ratio 1.25). The sensitivity of intraluminal appendiceal air in the obstructed segment for occult perforation was 36.9% with a specificity of 81.9%. The presence of intraluminal appendicoliths was strongly associated with advanced appendicitis and was a risk factor for perorationandnecrosisisthisreport.Infact,appendicoliths were found at a higher rate (nearly 36%) than the intraluminal airsign(21%).Previousreportsinsmallcohortsalsoshowedan association between appendicoliths and the severity of acute appendicitis in patients who underwent CT more than 10 hours after the onset of symptoms (13). These findings might be explained by the assumed pathophysiologyof acute appendicitis. An obstruction of the appendix causes dilatation and inflammation. It seems reasonable then that both an obstructing appendicolith and intraluminal air in the obstructed segment of the appendix would be associated with a higher incidence of complicated disease including perforation and necrosis.NotetheimportanceofclinicalcontextandCTsigns of appendicitisinregardtothe meaningof appendicolith since asymptomatic individuals may also have an appendicolith on CTwithunclearclinicalimplications(14).Itwillbeinteresting