Review question
To check the accuracy of magnetic resonance imaging (MRI), a medical imaging tool used for taking detailed pictures of the inside of the body, to test for appendicitis.
Why is diagnosing appendicitis important?
Appendicitis is a very common condition that is usually treated with emergency surgery, but it can be difficult to diagnose. Up to one in four patients may be incorrectly diagnosed with appendicitis. Tools such as MRI can help diagnose appendicitis quickly and early.
What was studied in this review?
We studied the accuracy of MRI for appendicitis in all patients.
What are the main results of the review?
We analysed the results of 58 studies with 7462 participants to calculate the accuracy of MRI. The results of these studies indicate that in theory, if MRI were to be used in 1000 patients with suspected appendicitis, where 250 patients actually had appendicitis, then:
• an estimated 250 patients will have an MRI result indicating appendicitis, 12 of whom will not actually have appendicitis; and
• of the 750 patients with a result indicating that appendicitis is not present, 30 will actually have appendicitis.
MRI remained very accurate when looking specifically at adults, pregnant women, and children.
How reliable are the results of the studies in this review?
There were problems with how most of the studies were conducted that may have resulted in MRI appearing more accurate than it actually is.
To whom do the results of this review apply?
The results apply to people with suspected appendicitis, including adults, pregnant women, and children. Most studies were conducted in Europe and North America in large university hospitals. Patients had often undergone an ultrasound scan without a clear result.
What are the key messages of this review?
Based on the studies included in this review, MRI seems to be a very accurate test for appendicitis. The chance of wrongly diagnosing someone with appendicitis or missing appendicitis was less than 5%. However, as most of the included studies had problems, we cannot trust their results completely. Although MRI is promising, until better studies have been performed, we cannot firmly recommend the use of MRI for the diagnosis of appendicitis.
How up-to-date is this review?
We searched for and used studies published up to February 2021.
MRI appears to be highly accurate in confirming and excluding acute appendicitis in adults, children, and pregnant women regardless of protocol. The methodological quality of the included studies was generally low due to incomplete and low standards of follow-up, so summary estimates of sensitivity and specificity may be biased. We could not assess the impact and direction of potential bias given the very low number of high-quality studies. Studies comparing MRI protocols were few, and although we found no influence of MRI protocol variables on the summary estimates of accuracy, our results do not rule out that some MRI protocols are more accurate than others.
Appendicitis remains a difficult disease to diagnose, and imaging adjuncts are commonly employed. Magnetic resonance imaging (MRI) is an imaging test that can be used to diagnose appendicitis. It is not commonly regarded as a first-line imaging test for appendicitis, but the reported diagnostic accuracy in some studies is equivalent to computed tomography (CT) scans. As it does not expose patients to radiation, it is an attractive imaging modality, particularly in women and children.
The primary objective was to determine the diagnostic accuracy of MRI for detecting appendicitis in all patients.
Secondary objectives:
To investigate the accuracy of MRI in subgroups of pregnant women, children, and adults.
To investigate the potential influence of MRI scanning variables such as sequences, slice thickness, or field of view.
We searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, and Embase until February 2021. We searched the references of included studies and other systematic reviews to identify further studies. We did not exclude studies that were unpublished, published in another language, or retrospective.
We included studies that compared the outcome of an MRI scan for suspected appendicitis with a reference standard of histology, intraoperative findings, or clinical follow-up. Three study team members independently filtered search results for eligible studies.
We independently extracted study data and assessed study quality using the Quality Assessment of Studies of Diagnostic Accuracy - Revised (QUADAS-2) tool. We used the bivariate model to calculate pooled estimates of sensitivity and specificity.
We identified 58 studies with sufficient data for meta-analysis including a total of 7462 participants (1980 with and 5482 without acute appendicitis). Estimates of sensitivity ranged from 0.18 to 1.0; estimates of specificity ranged from 0.4 to 1.0. Summary sensitivity was 0.95 (95% confidence interval (CI) 0.94 to 0.97); summary specificity was 0.96 (95% CI 0.95 to 0.97). Sensitivity and specificity remained high on subgroup analysis for pregnant women (sensitivity 0.96 (95% CI 0.88 to 0.99); specificity 0.97 (95% CI 0.95 to 0.98); 21 studies, 2282 women); children (sensitivity 0.96 (95% CI 0.95 to 0.97); specificity 0.96 (95% CI 0.92 to 0.98); 17 studies, 2794 children); and adults (sensitivity 0.96 (95% CI 0.93 to 0.97); specificity 0.93 (95% CI 0.80 to 0.98); 9 studies, 1088 participants), as well as different scanning techniques. In a hypothetical cohort of 1000 patients, there would be 12 false-positive results and 30 false-negative results. Methodological quality of the included studies was poor, and the risk of bias was high or unclear in 53% to 83% of the QUADAS-2 domains.