Magnetic resonance imaging (MRI) for diagnosis of acute appendicitis

BACKGROUND

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.

OBJECTIVES

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.

SEARCH METHODS

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 We did not exclude studies that were unpublished, published in another language, or retrospective.

SELECTION CRITERIA

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.

DATA COLLECTION AND ANALYSIS

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.

MAIN RESULTS

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.

AUTHORS' CONCLUSIONS

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.

ACR Appropriateness Criteria® Suspected Appendicitis-Child

Acute appendicitis represents the most common abdominal surgical urgency/emergency in children. Imaging remains a central tool in the diagnosis of acute appendicitis and has been shown to facilitate management and decrease the rate of negative appendectomies. The initial consideration for imaging in a child with suspected acute appendicitis is based on clinical assessment, which can be facilitated with published scoring systems. The level of clinical risk (low, intermediate, high) and the clinical scenario (suspicion for complication) define the need for imaging and the optimal imaging modality. In some situations, no imaging is required, while in others ultrasound, CT, or MRI may be appropriate. This review frames the presentation of suspected acute appendicitis in terms of the clinical risk and also discusses the unique situations of the equivocal or nondiagnostic initial ultrasound examination and suspected appendicitis with suspicion for complication (eg, bowel obstruction). The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.

Cost-effectiveness of Imaging Protocols for Suspected Appendicitis

BACKGROUND

Inaccurate diagnosis of appendicitis leads to increased costs and morbidity. Ultrasound costs less than computed tomography (CT) or MRI but has lower sensitivity and may not visualize the appendix.

METHODS

We conducted a cost-effectiveness analysis using a decision-analytic model of 10 imaging strategies for suspected appendicitis in a hypothetical cohort of patients: no imaging with discharge or surgery; CT only; MRI only; or staged approach with CT or MRI after 1) negative ultrasound result or ultrasound without appendix visualization, 2) ultrasound without appendix visualization, or 3) ultrasound without appendix visualization but with secondary signs of inflammation. Inputs were derived from published literature and secondary data (quality-of-life and cost data). Sensitivity analyses varied risk of appendicitis and proportion of visualized ultrasound. Outcomes were effectiveness (quality-adjusted life-years [QALYs]), total direct medical costs, and cost-effectiveness (cost per QALY gained).

RESULTS

The most cost-effective strategy for patients at moderate risk for appendicitis is initial ultrasound, followed by CT if the appendix is not visualized but secondary signs are present (cost of $4815.03; effectiveness of 0.99694 QALYs). Other strategies were well above standard willingness-to-pay thresholds or were more costly and less effective. Cost-effectiveness was sensitive to patients' risk of appendicitis but not the proportion of visualized appendices.

CONCLUSIONS

Tailored approaches to imaging based on patients' risk of appendicitis are the most cost-effective. Imaging is not cost-effective in patients with a probability <16% or >95%. For moderate-risk patients, ultrasound without secondary signs of inflammation is sufficient even without appendix visualization.

Appendicitis: Role of MRI

The diagnosis of pediatric appendicitis can be difficult, with a substantial proportion misdiagnosed based on clinical features and laboratory tests alone. Accordingly, advanced imaging with ultrasound (US), computed tomography (CT), and/or magnetic resonance imaging has become routine for most children undergoing diagnostic evaluation for appendicitis. There is increasing interest in the use of US as the primary imaging modality and reserving CT as a secondary diagnostic modality in equivocal cases. Magnetic resonance imaging, using a rapid protocol, without contrast or sedation, has been found to be highly sensitive and specific in the evaluation of children with acute right lower quadrant pain in a number of studies. Because magnetic resonance imaging has the advantage over CT of not using contrast or ionizing radiation, it may replace CT in many instances, whether after US as part of a stepwise imaging algorithm or as a primary imaging modality. Accessibility and cost, however, limit its more widespread use currently.

Case based simulation in MRI for suspected appendicitis in children

PURPOSE

To establish the effect on diagnostic confidence of a simulation setting, in which radiologists re-interpret anonymized pediatric MRI cases.

MATERIALS

In this IRB-approved study, participants completed surveys rating confidence before and after interpreting 10 MRI cases for suspected appendicitis in children.

RESULTS

18 radiologists (4 faculty, 5 fellows, and 9 residents) correctly identified an average of 7.44 cases (range 5-9). Self-described confidence regarding technique and interpretation increased from 2.0 (SD 0.77) and 2.33 (SD 0.69) to 2.83 (SD 0.71) and 2.94 (SD 0.73), respectively.

CONCLUSION

Simulated interpretation of pediatric MRI in suspected appendicitis results in increased self-describe confidence without requiring additional capital/equipment expenses.

Association of Hospital Resources and Imaging Choice for Appendicitis in Pediatric Emergency Departments

OBJECTIVE

Abdominal pain and concern for appendicitis are common chief complaints in patients presenting to the pediatric emergency department (PED). Although many professional organizations recommend decreasing use of computed tomography (CT) and choosing ultrasound as first-line imaging for pediatric appendicitis, significant variability persists in imaging utilization. This study investigated practice variation across children's hospitals in the diagnostic imaging evaluation of appendicitis and determined hospital-level characteristics associated with the likelihood of ultrasound as the first imaging modality.

METHODS

This was a multicenter (seven children's hospitals) retrospective investigation. Data from chart review of 160 consecutive patients aged 3-18 years diagnosed with appendicitis from each site were compared with a survey of site medical directors regarding hospital resource availability, usual practices, and departmental-level demographics.

RESULTS

In the diagnostic evaluation of 1,090 children with appendicitis, CT scan was performed first for 22.4% of patients, with a range across PEDs of 3.1% to 83.8%. Ultrasound was performed for 54.0% of patients with a range of 2.5% to 96.9%. The only hospital-level factor significantly associated with ultrasound as the first imaging modality was 24-hour availability of in-house ultrasound (odds ratio = 29.2, 95% confidence interval = 1.2-691.8).

CONCLUSION

Across children's hospitals, significant practice variation exists regarding diagnostic imaging in the evaluation of patients with appendicitis. Variation in hospital-level resources may impact the diagnostic evaluation of patients with appendicitis. Availability of 24-hour in-house ultrasound significantly increases the likelihood of ultrasound as first imaging and decreases CT scans. Hospitals aiming to increase the use of ultrasound should consider adding 24-hour in-house coverage.

Imaging Utilization for the Diagnosis of Appendicitis in Stand-Alone Children's Hospitals in the United States: Trends and Costs

OBJECTIVE

To describe the imaging utilization patterns for the diagnosis of appendicitis among children's hospitals in the United States over the last 10 years (2005-2014).

METHODS

All patients with a primary discharge diagnosis of appendicitis included in a large administrative database of 45 pediatric institutions in the United States between 2005 and 2014 were selected. Demographics, imaging utilization, and costs were described.

RESULTS

In all, 96,786 children with appendicitis (59% boys, 41% girls; mean age: 9.9 years) were studied. The average length of stay decreased from 5.0 days in 2005 to 3.4 days in 2014 (P < .01). The percentage of patients undergoing CT increased between 2005 and 2007 from 59.1% to 62.6%, respectively, followed by a decrease from 62.6% to 32.7% in 2014 (r² = 0.93). Radiograph utilization decreased from 14.2% in 2005 to 3.6% in 2014 (r² = 0.93), and ultrasound and MRI increased from 25% and 0.03% in 2005 to 61% and 1.0% in 2014 (r² = 0.97 and 0.64), respectively. The mean total hospital costs increased from $11,700 in 2005 to $16,500 in 2014; imaging costs increased only slightly from $3,205 to $3,259. The imaging fraction of hospital costs decreased from 27.5% to 19.8%.

CONCLUSION

There has been a significant decrease in utilization of CT and radiographs for the management of appendicitis in children, and ultrasound has continued to increase. Imaging costs have remained stable in comparison to rising hospital costs, generating a drop in the fraction of costs related to imaging.