CT Diagnosis of Acute Appendicitis
ABSTRACT & COMMENTARY
Synopsis: The CT scan can be a useful tool in the acute evaluation of the patient with abdominal pain and possible APPDX; however, its use is probably not indicated in the majority of cases of APPDX and will probably be most useful in the questionable case.
Source: Rao PM, et al. N Engl J Med 1998;338:141-146.
Rao and associates performed a prospective case series investigating the effect of CT scan on patients presenting with clinical features suggestive of acute appendicitis (APPDX) who were to be admitted for further observation or taken for urgent laparotomy. Of importance, these patients were all seen in consultation by the surgeon prior to study entry. One hundred consecutive ED patients underwent a helical CT of the abdomen limited to the appendix, which was interpreted by an attending radiologist with the result provided to the clinician within one hour. Bowel contrast was administered rectally, and intravenous contrast was not administered. Prior to performance of the study, the clinician was asked the degree of suspicion for the diagnosis of APPDX and the intended treatment plan (inpatient observation or urgent laparotomy). Treatment plan modifications following CT scan results were also examined. The effect of appendiceal CT scan on hospital-based costs was also investigated. Outcomes were determined by the operative findings and pathological specimens for surgical cases and clinical follow-up at two months for nonoperative patients.
Fifty-three patients had APPDX and 47 had alternative diagnoses, including mesenteric adenitis, nonspecific abdominal pain, ovarian cyst, right-sided colitis, sigmoid diverticulitis, and biliary colic. Eighty-six patients had a specific clinical diagnosis; the CT scan revealed this diagnosis in 81 cases. The clinical syndromes not diagnosed by CT scan included biliary colic (2), urinary tract infection (1), endometriosis (1), and appendicitis (1); the remaining patients were ultimately diagnosed with nonspecific abdominal pain and presumably did well at follow-up.
The appendiceal CT was 98% sensitive and 98% specific for the diagnosis of APPDX; the CT scan also demonstrated a 98% positive predictive value, a 98% negative predictive value, and an overall accuracy rate of 98% for the diagnosis of APPDX. In the entire study population, the CT scan provided a false negative result in only one patient. The CT scan findings led to changes in the intended treatment plan for 59 patients, including the prevention of unnecessary surgery (13), admission to the hospital for observation (18), admission to the hospital for preoperative monitoring prior to appendectomy (21), and admission to the hospital for additional evaluation and treatment of other conditions (11). Considering the costs of the CT scan, unnecessary surgery, and unnecessary admission, Rao et al reported an overall savings of $447 per patient.
COMMENT BY WILLIAM J. BRADY, MD
In most cases, acute appendicitis does not represent a diagnostic challenge; approximately 70% of cases of APPDX are reasonably straightforward and are correctly made prior to surgery. The remaining 30% of cases present with some atypical or challenging features, such as young patient age, unusual pain location, or prolonged/intermittent pain. Patients in this presentation category are not infrequently misdiagnosed on initial contact. These patients with delayed diagnosis are at extreme risk of perforation with significant associated morbidity. Further, missed APPDX is the leading successful malpractice claim against emergency physicians in the United States.
Rao et al provide yet another useful tool to the physician in the acute evaluation of the patient with abdominal pain and possible APPDX. The CT scan, however, probably is not indicated in the majority of cases of APPDX, as most cases do not present a diagnostic challenge. The CT scan will probably be most useful in the questionable case. The use of CT scan in this type of patient will assist in several ways; it can 1) "rule-in" APPDX; 2) "rule-out" APPDX and provide, in many cases, the alternative diagnosis; 3) limit the number of unnecessary laparotomies; and 4) suggest the appropriate therapy in the early stages of evaluation. One would hope that the CT scan would not become a standard investigation in the evaluation of all patients with lower abdominal pain; rather, its most appropriate use will likely be found in the patients with an atypical or questionable presentation. Lastly, among experienced general radiologists with minimal instruction, interpretation of the scan reportedly is not problematic; the issue of operator expertise, a problem with the use of ultrasound in the evaluation of possible APPDX, will not introduce limitation to its use. (Dr. Brady is Assistant Professor of Emergency Medicine and Internal Medicine, and Medical irector, Chest Pain Center, University of Virginia, Charlottesville.)