MRI of the normal appendix in children: data toward a new reference standard

Comparison of MRI appendix biometrics in children with and without acute appendicitis

OBJECTIVES

The goal of this study is to improve MRI-specific diagnostic criteria for pediatric appendicitis through comparison of normal and abnormal appendix-related imaging features.

METHODS

A retrospective multireader-multicase design was used, including non-contrast MRI performed for suspected pediatric appendicitis following non-diagnostic US from January 2014 to December 2017. Positive diagnosis was defined by surgical pathology or symptom resolution after antibiotics. Four pediatric radiologists independently graded study biometrics while blinded to clinical data. Balanced complete block design was used to determine performance characteristics.

RESULTS

Global diagnosis of appendicitis (208 studies) had sensitivity 90.6% and specificity 97.7%. Median appendix diameter was 10.4 mm among positive cases and 5.8 mm among negative cases (p < 0.001) with an optimal diagnostic cutoff of 7.5 mm (sensitivity 89.4%, specificity 86.5%). Median appendix wall thickness was 2.6 mm among positive cases and 1.7 mm among negative cases (p < 0.001) with an optimal diagnostic cutoff of 2.3 mm (sensitivity 63.1%, specificity 82.9%). Performance characteristics for qualitative appendix features included distinguishable appendix luminal signal (sensitivity 89.6%, specificity 83.7%), intraluminal fluid-signal intensity (sensitivity 63.6%; specificity 52.3%), intraluminal signal intermediate between fluid and bowel wall (sensitivity 91.0%; specificity 37.1%), appendicolith (sensitivity 34.9%; specificity 100.0%), intraluminal layering (sensitivity 25.9%; specificity 100.0%), hyperintense appendix wall signal (sensitivity 31.7%; specificity 100.0%), periappendiceal fluid (sensitivity 66.8%; specificity 72.5%), periappendiceal fatty edema (sensitivity 91.3%; specificity 94.5%), and free pelvic fluid (sensitivity 88.5%; specificity 26.0).

CONCLUSIONS

This study provides MRI-specific performance of pediatric appendicitis quantitative and qualitative biometrics with peri-appendiceal fatty edema, appendix diameter > 7.5 mm, and distinguishable appendix luminal signal demonstrating the highest overall accuracy.

KEY POINTS

• This retrospective multireader-multicase study characterized magnetic resonance imaging-specific diagnostic accuracy of quantitative and qualitative biometrics for pediatric appendicitis. • The optimal quantitative diagnostic thresholds for an abnormal pediatric appendix at MRI included diameter and wall thickness of 7.5 mm and 2.3 mm, respectively. • Qualitative imaging biometrics with high specificity for pediatric appendicitis on MRI included the presence of distinguishable appendix lumen signal from wall signal, appendicolith, intraluminal fluid-fluid layer, appendix wall hyperintensity, and peri-appendiceal fatty edema.

Reference growth curves for normal appendiceal diameter in childhood

The aim of this study was to investigate the relationship between the appendiceal diameter (AD) and age, sex, height, and body weight in children and to verify how does the normal AD grows in childhood. We evaluated the AD of patients younger than 16 years of age who underwent laparoscopic surgery at our hospital. We statistically examined the relationship between the AD and the age, sex, height, and weight. A final cohort of 188 patients participated in the study. The median AD for the sample population was 5 mm (range, 3.2–8.1). There was no significant difference in the AD between males and females in the multivariate analysis (P = 0.500). There was a positive correlation between the age and the AD (R = 0.396, P < 0.001). The AD had a significant positive correlation with the height and weight (P < 0.001, P < 0.001, respectively). The reference curve with regard to the AD can be useful in clinical situations, although it should be kept in mind that the range of individual differences in AD is large, and the growth degree by age is not uniform during childhood.

Accuracy of unenhanced, non-sedated MRI in the diagnosis of acute appendicitis in children

BACKGROUND

Children with suspected appendicitis generally undergo an ultrasound (most commonly) or a CT scan (rarely) as the first imaging study. At our hospital, patients with non-diagnostic ultrasound or CT scan results undergo a non-contrast (unenhanced), non-sedated MRI. We aimed to determine the accuracy of this study for this purpose in a large cohort of children.

METHODS

A retrospective review of all unenhanced, non-sedated MRIs done for suspected appendicitis was performed from January 2014 to December 2018. MRI reports were correlated with pathology reports in cases that underwent appendectomy, and with clinical outcomes if no operation was done (clinical follow up: 30d). No patient was treated for appendicitis non-operatively.

RESULTS

Three hundred fifty unenhanced, non-sedated MRIs were done and reviewed with median age: 12 (3 to 18) years. Sixty-five (18.6%) MRIs were positive for appendicitis, and 62 of those underwent appendectomy (3 excluded clinically). Pathology was positive in 59/62 cases. 256 (73.1%) MRIs were negative for appendicitis. Six cases underwent appendectomy (persistent symptoms). Pathology was positive in 2/6 cases. The overall diagnostic accuracy was: sensitivity 96.7% (95% CI: 88.6-99.6), specificity 97.7% (95% CI: 95.0-99.1), PPV: 90.8% (95% CI: 81.6-95.6; false positives 6/65), and NPV: 99.2% (95% CI: 97.0-99.8; false negatives 2/254). Twenty-nine (8.3%) MRIs were non-diagnostic. None of those 29 cases had appendicitis (4 negative pathology, 25 excluded clinically).

CONCLUSIONS

The unenhanced, non-sedated MRI is highly accurate for the diagnosis of appendicitis in children. It should be considered as an alternative to CT in the work-up of patients with suspected appendicitis to eliminate the risks associated with ionizing radiation.

LEVEL OF EVIDENCE

Level IV.

Falling through the worm hole: an exploration of the imaging workup of the vermiform appendix in the pediatric population

Despite the thousands of articles discussing appendicitis in the literature, the dilemma of how to best diagnosis and manage pediatric appendicitis remains unsettled. Over the past decade, evidence has been mounting about the use of antibiotics as the sole therapy in uncomplicated appendicitis in the adult population. This debate has even recently bled over into the lay press. While this change in practice pattern is still in its infancy for the pediatric population, radiologists should be aware of this change in therapy and how it can impact the imaging work-up and relevant findings. This article concisely summarizes the imaging findings and various imaging pathways to arrive at the diagnose of appendicitis with an emphasis of how to best be of use to our surgical colleagues in this evolving paradigm. It also highlights venues for further research, namely increasing accuracy of differentiating complicated from uncomplicated appendicitis.

Visualization of the normal appendix in children: feasibility of a single contrast-enhanced radial gradient recalled echo MRI sequence

BACKGROUND

Magnetic resonance imaging (MRI) assessment for appendicitis is limited by exam time and patient cooperation. The radially sampled 3-dimensional (3-D) T1-weighted, gradient recalled echo sequence (radial GRE) is a free-breathing, motion robust sequence that may be useful in evaluating appendicitis in children.

OBJECTIVE

To compare the rate of detection of the normal appendix with contrast-enhanced radial GRE versus contrast-enhanced 3-D GRE and a multi-sequence study including contrast-enhanced radial GRE.

MATERIALS AND METHODS

This was a retrospective study of patients ages 7-18 years undergoing abdominal-pelvic contrast-enhanced MRI between Jan. 1, 2012, and April 1, 2016. Visualization of the appendix was assessed by consensus between two pediatric radiologists. The rate of detection of the appendix for each sequence and combination of sequences was compared using a McNemar test.

RESULTS

The rate of detection of the normal appendix on contrast-enhanced radial GRE was significantly higher than on contrast-enhanced 3-D GRE (76% vs. 57.3%, P=0.003). The rate of detection of the normal appendix with multi-sequence MRI including contrast-enhanced radial GRE was significantly higher than on contrast-enhanced 3-D GRE (81.3% vs. 57%, P<0.001). There was no significant difference between the rate of detection of the normal appendix on contrast-enhanced radial GRE alone and multi-sequence MRI including contrast-enhanced radial GRE (76% vs. 81.3%, P=0.267).

CONCLUSION

Contrast-enhanced radial GRE allows superior detection of the normal appendix compared to contrast-enhanced 3-D GRE. The rate of detection of the normal appendix on contrast-enhanced radial GRE alone is nearly as good as when the contrast-enhanced radial GRE is interpreted with additional sequences.

MRI for Pediatric Appendicitis in an Adult-Focused General Hospital: A Clinical Effectiveness Study-Challenges and Lessons Learned

OBJECTIVE

The objective of our study was to determine the feasibility and accuracy of MRI for pediatric appendicitis in an adult-predominant general hospital setting where non-pediatric-trained radiologists routinely interpret the studies.

MATERIALS AND METHODS

MRI was performed in pediatric patients with equivocal ultrasound (US) findings and persistent clinical concern for appendicitis. Neither IV contrast material nor a sedative was administered. Our MRI protocol evolved early during the study period, quickly settling on three sequences (total scanning time, 11 minutes). The clinical reference standard for statistical analysis was appendicitis diagnosed on operative or pathology report; 95% Clopper-Pearson CIs were calculated.

RESULTS

Between 2012 and 2016, 528 pediatric patients (mean age, 9.9 years; age range, 1-17 years) underwent MRI after US evaluation yielded equivocal findings: 10.4% (55/528) of patients were found to have surgically proven or pathologically proven appendicitis. Sensitivity and specificity of MRI for appendicitis were 96.4% and 98.9%, respectively. Positive and negative predictive values were 91.2% and 99.6%. A normal appendix and abnormalities not involving the appendix were identified on MRI in 21.6% (114/528) of patients.

CONCLUSION

Our data show that unenhanced MRI for suspected appendicitis in pediatric patients is clinically effective when performed in a nonpediatric hospital setting with nonpediatric radiologists, emergency physicians, and surgeons.

Practical Imaging Strategies for Acute Appendicitis in Children

OBJECTIVE

Diagnosing pediatric appendicitis is difficult because clinical findings are nonspecific. Improved accuracy can be obtained with ultrasound (US), CT, or MRI, despite considerable variation in their use at different institutions. This article reviews the evidence for best practices in imaging pediatric appendicitis.

CONCLUSION

When each modality is optimally used, a stepwise imaging approach that begins with graded compression US and proceeds to CT or MRI in select cases is currently best practice.

Visibility of Normal Appendix on CT, MRI, and Sonography: A Systematic Review and Meta-Analysis

OBJECTIVE

The purpose of the present study is to assess the visibility of the normal appendix on CT, MRI, or ultrasound (US) images of a healthy population.

MATERIALS AND METHODS

The MEDLINE and EMBASE databases were searched to identify articles on the rates of detection of a normal appendix on CT, MRI, or US that appeared in the literature published up to January 20, 2017. Pooled detection rates were assessed using random-effects modeling, and rates associated with different imaging modalities were compared. Meta-regression analyses were performed to assess factors influencing detection rates and heterogeneity.

RESULTS

Thirty-two studies (21 CT studies with 5296 patients, 7 MRI studies with 600 patients, and 4 US studies with 1221 patients) were included in our meta-analysis. The overall normal appendix detection rate tended to be highest for CT (84%), followed by US (71%) and MR (69%), but no statistically significant differences were noted (for CT vs MRI, p = 0.16; for CT vs US, p = 0.23; and for MRI vs US, p = 0.91). Meta-regression analyses of the appendix detection rate with CT revealed that the year of publication of the study, the number of CT channels, and slice thickness affected study heterogeneity.

CONCLUSION

Normal appendixes seemed to be more visible on CT than on MRI or US, although this finding did not have statistical significance. With respect to CT, detection of normal appendixes was significantly better when more channels and thinner slices were used.

Performance characteristics of magnetic resonance imaging without contrast agents or sedation in pediatric appendicitis

BACKGROUND

Magnetic resonance imaging (MRI) has emerged as a promising modality for evaluating pediatric appendicitis. However optimal imaging protocols, including roles of contrast agents and sedation, have not been established and diagnostic criteria have not been fully evaluated.

OBJECTIVE

To investigate performance characteristics of rapid MRI without contrast agents or sedation in the diagnosis of pediatric appendicitis.

MATERIALS AND METHODS

We included patients ages 4-18 years with suspicion of appendicitis who underwent rapid MRI between October 2013 and March 2015 without contrast agent or sedation. After two-radiologist review, we determined performance characteristics of individual diagnostic criteria and aggregate diagnostic criteria by comparing MRI results to clinical outcomes. We used receiver operating characteristic (ROC) curves to determine cut-points for appendiceal diameter and wall thickness for optimization of predictive power, and we calculated area under the curve (AUC) as a measure of test accuracy.

RESULTS

Ninety-eight MRI examinations were performed in 97 subjects. Overall, MRI had a 94% sensitivity, 95% specificity, 91% positive predictive value and 97% negative predictive value. Optimal cut-points for appendiceal diameter and wall thickness were ≥7 mm and ≥2 mm, respectively. Independently, those cut-points produced sensitivities of 91% and 84% and specificities of 84% and 43%. Presence of intraluminal fluid (30/33) or localized periappendiceal fluid (32/33) showed a significant association with acute appendicitis (P<0.01), with sensitivities of 91% and 97% and specificities of 60% and 50%. For examinations in which the appendix was not identified by one or both reviewers (23/98), the clinical outcome was negative.

CONCLUSION

Rapid MRI without contrast agents or sedation is accurate for diagnosis of pediatric appendicitis when multiple diagnostic criteria are considered in aggregate. Individual diagnostic criteria including optimized cut-points of ≥7 mm for diameter and ≥2 mm for wall thickness demonstrate high sensitivities but relatively low specificities. Nonvisualization of the appendix favors a negative diagnosis.