Ultrasound evaluation of appendicitis: importance of the 3 × 2 table for outcome reporting

Determining the impact of body mass index on ultrasound accuracy for diagnosing appendicitis: Is it less useful in obese children?

BACKGROUND

Ultrasonography (US) is the preferred imaging for suspected pediatric appendicitis. We hypothesize that children with elevated Body-Mass-Index-for-age percentile (BMIP) may be more likely to have an inaccurate or equivocal (IE) US.

METHODS

After IRB approval, a four-year review was performed on pediatric patients evaluated for appendicitis by US. The CDC BMIP Calculator was used. IE subgroups were analyzed together for comparison against the accurate group.

RESULTS

1059 patients were included: median age 11.3 years (IQR: 8.2, 14.6), 506 (47.8%) males. Median BMIP was 65.9 (IQR: 33.9, 89.6). US accurately diagnosed 857 (80.9%), incorrectly diagnosed 76 (7.2%), 126 (11.9%) were equivocal. Overall sensitivity was 0.85, specificity 0.96, PPV 0.93 and NPV 0.91. Obese children (BMIP ≥95%), had higher odds of IE US (OR: 1.86, 95% CI: 1.28, 2.70; p = 0.001). When analyzed by sex, risk increased in obese males (OR: 2.55, 95% CI:1.53, 4.24; p = 0.0003) but normalized in obese females (OR: 1.30, 95% CI:0.74, 2.28; p = 0.35).

CONCLUSIONS

An elevated BMIP may increase difficulty in visualizing the appendix, resulting in inaccurate or equivocal findings. This risk is seen specifically in obese males. If US findings do not correlate with clinical assessment in obese children with abdominal pain, further evaluation may be warranted.

Diagnostic performance of US for suspected appendicitis: Does multi-categorical reporting provide better estimates of disease in adults, and what factors are associated with false or indeterminate results?

PURPOSE

To identify factors associated with false or indeterminate US result for suspected appendicitis, and assess whether multi-categorical reporting of US yields more precise estimates regarding the probability of appendicitis.

METHODS

562 US examinations for suspected appendicitis between May 2013-April 2015 were categorized as true (77/562 true positives or true negatives) or false/indeterminate (485/562 false negatives, false positives or indeterminates) based on results from a prior study. Of 541 examinations with images available retrospectively, a category of A-E was assigned as follows: non-visualized appendix with secondary findings (A) absent or (B) present; appendix visualized and considered (C) negative, (D) equivocal, or (E) positive for appendicitis. The following factors were recorded: age; sex; scan time (daytime vs. off-hours); resident/fellow involvement; abdominal subspecialty radiologist; radiologist experience (>5 years or not); and tenderness on interrogation. Associations between factors and US result were assessed (t-tests, Fisher's exact test and multivariate logistic regression).

RESULTS

The true group had proportionally more males (18/77 (23.4%) vs. 66/485 (13.6%), p = 0.04) and patients with sonographic tenderness (43/77 (55.8%) vs. 132/353 (27.3%), p < 0.0001). There was no significant difference or association with other factors. On multivariate logistic regression, false/indeterminate results were 1.9 times (95% CIs 1.0-3.5) more likely among females and 3.8 times more likely in the absence of tenderness (95% CIs 2.3-6.4). The proportion of patients with appendicitis in categories A-E was 34/410 (8.3%), 24/44 (54.5%), 0/18 (0%), 0/3 (0%) and 61/66 (92.4%), respectively.

CONCLUSIONS

Females and absence of tenderness were associated with a false/indeterminate US. Categorical reporting provides more granular estimates of the post-test probability of appendicitis.

Ultrasound for Suspected Acute Appendicitis in Adult Women Under Age 40: An Evaluation of On-Call Radiology Resident Scanning

RATIONALE AND OBJECTIVES

At our institution, on-call radiology residents perform emergent ultrasounds (US) outside of departmental working hours. The aim of the study was to evaluate radiology resident-performed US for clinically suspected acute appendicitis in women under the age of 40.

MATERIALS AND METHODS

Retrospective review of 104 consecutive US scans outside of departmental working hours by radiology residents, and 104 consecutive US studies scanned during departmental working hours by sonographers, in women under the age of 40 for clinically suspected appendicitis .

RESULTS

Appendix visualization rate was 27% for the resident group (sonographer group: 30%, p = 0.759). The sensitivity and specificity of US for appendicitis were 63% (95% confidence interval: 41%-81%) and 98% (95% CI: 91%-100%), respectively for the resident group (sonographer group: 69% [95% CI: 41%-89 %] and 98% [95% CI: 92%-100%], respectively). An alternative cause for right lower quadrant pain was offered in 17% of resident group cases (sonographer group: 21%, p = 0.598). Follow-up CT or MRI was performed in 47% of resident cases (sonographer group: 44%, p = 0.781). Residents performed more focused US (i.e. not imaging the pelvic organs), at 34% (sonographer group: 1%, p < 0.001). When only focused scanning was performed by residents, there was a trend toward increased downstream imaging (CT or MRI), odds ratio = 2.76 (95% CI: 0.99-7.70).

CONCLUSIONS

Out-of-hours US scans performed by radiology residents had similar performance characteristics compared to departmental sonographers. We discovered an increased rate of downstream imaging in cases in which residents performed limited scans and did not document visualization of the pelvic organs.

Ultrasound and CT in the Diagnosis of Appendicitis: Accuracy With Consideration of Indeterminate Examinations According to STARD Guidelines

OBJECTIVE. The objective of our study was to determine the accuracy of ultrasound (US) and CT in diagnosing appendicitis at our institution while taking into account the number of indeterminate examinations in accordance with the Standards for Reporting Diagnostic Accuracy (STARD) guidelines. MATERIALS AND METHODS. We retrospectively evaluated 790 patients who underwent US, CT, or both for evaluation of suspected appendicitis between May 1, 2013, and April 30, 2015. Patient characteristics and US and CT examination results were recorded. The reference standard was histopathology or 3 months of medical record follow-up if surgery was not performed; 3 × 2 tables were generated, and sensitivity, specificity, overall test yield, and accuracy were calculated according to STARD guidelines. For surgical cases, time to surgery (one-way ANOVA) was compared among patients who underwent US alone, CT alone, or both US and CT. RESULTS. A total of 473 of 562 US examinations had indeterminate findings (overall test yield, 15.8%); sensitivity and specificity in the 89 diagnostic examinations were 98.5% and 54.2%, respectively. Thirteen of 522 CT examinations were indeterminate (overall test yield, 97.5%); sensitivity and specificity in the remaining 509 CT examinations were 98.9% and 97.2%, respectively. Taking indeterminate studies into account, the accuracy was 13.7% for US and 95.6% for CT. The negative appendectomy rates were 17.7% (11/62) for US and 3.3% (9/276) for CT (p = 0.0002). Time to surgery was longer for patients who underwent US and CT (mean ± SD, 17.7 ± 8.9 hours) than US alone (12.9 ± 6.4 hours; p = 0.002) but was not longer for patients who underwent CT alone (16.3 ± 8.4 hours; p = 0.45). CONCLUSION. At our institution, a large proportion of US examinations are indeterminate for appendicitis. CT is the preferred first-line imaging test for evaluating appendicitis in nonobstetric adult patients.

Utility of applying white blood cell cutoffs to non-diagnostic MRI and ultrasound studies for suspected pediatric appendicitis

BACKGROUND

Non-contrast magnetic resonance imaging (MRI) and ultrasound studies in pediatric patients with suspected appendicitis are often non-diagnostic. The primary objective of this investigation was to determine if combining these non-diagnostic imaging results with white blood cell (WBC) cutoffs improves their negative predictive values (NPVs).

METHODS

A retrospective chart review was conducted including patients ≤18 years old with suspected appendicitis who had MRI performed with or without a preceding ultrasound study in a pediatric emergency department. Imaging results were sorted into 2 diagnostic and 5 non-diagnostic categories. NPVs were calculated for the non-diagnostic MRI and ultrasound categories with and without combining them with WBC cutoffs of <10.0 and <7.5 × 10⁹/L.

RESULTS

Of the 612 patients with MRI studies included, 402 had ultrasound studies performed. MRI with incomplete visualization of a normal appendix without secondary signs of appendicitis had an NPV of 97.9% that changed to 98.1% and 98.2% when combined with WBC cutoffs of <10.0 and <7.5, respectively. Ultrasound studies with incomplete visualization of a normal appendix without secondary signs had an NPV of 85.3% that improved to 94.8% and 96.5% when combined with WBC cutoffs of <10.0 and <7.5, respectively.

CONCLUSIONS

In pediatric patients with suspected appendicitis, MRI studies with incomplete visualization of a normal appendix without secondary signs have a high NPV that does not significantly change with the use of these WBC cutoffs. In contrast, combining WBC cutoffs with ultrasound studies with the same interpretation identifies low-risk groups.

The clinical value of pathology tests and imaging study in the diagnosis of acute appendicitis

OBJECTIVE

To explore the diagnostic accuracy of acute appendicitis among different patient groups and evaluate the statistical diagnostic values of common pathology and imaging tests for the diagnosis of acute appendicitis.

MAIN MEASURES

Proportions of histology-proven appendicitis in different patient groups. Statistical parameters including sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), positive likelihood ratio (+LR), negative likelihood ratio (-LR) and diagnostic odds ratio (DOR) between the histology-proven appendicitis and abnormal results of U/S, CT, WCC, CRP, bilirubin, pancreatic, and combined test results of WCC and CRP.

RESULTS

Our data showed that up to 25.7% of patients underwent appendectomy has normal appendix. Appendicitis is often accurately diagnosed among male patients, up to 90.3% of the time, while misdiagnosis of appendicitis among young females (<40 years old) is significantly high, up to 30.9%. CT has high diagnostic performance index for appendicitis, sensitivity > 90%, and no individual pathology test out of those examined can rival the sensitivity of CT. Nevertheless, by examining the combined results of WCC and CRP, we found that abnormal results in one or both these yields sensitivity similar to CT scans in detecting acute appendicitis, up to 95%.

CONCLUSION

Young female patients have highest risk of being falsely diagnosed with acute appendicitis and hence unnecessary surgery. Bilirubin and lipase exhibit no correlations with acute appendicitis. Combined interpretation of WCC or CRP abnormal results yields competitive sensitivity as CT. Hencewe would suggest that, under the appropriate clinical context, one can use both WCC and CRP as a simple tool to support the diagnosis of appendicitis. If both tests show normal results, we would highly recommend considering alternative diagnosis.

The current utility of ultrasound in the diagnosis of acute appendicitis

The purpose of this study is to evaluate the current performance of ultrasound in the diagnosis of acute appendicitis. Retrospectively, patients who presented to a single institution between 2011 and 2012 were included. Diagnostic accuracy was calculated, with surgery considered gold-standard. Our data demonstrates that US relative to surgery-confirmed appendicitis has a sensitivity and specificity of 48.4% and 97.9%, respectively. The diagnostic accuracy was further increased when there was a low pre-test probability, with a NPV of up to 96.6%. Ultrasound has a strong PPV in the diagnosis of acute appendicitis, and in equivocal cases, the NPV is reliable.

Pediatric appendiceal ultrasound: accuracy, determinacy and clinical outcomes

BACKGROUND

Ultrasonography is considered the most appropriate initial imaging study in the evaluation of acute appendicitis in children but has recently come under criticism with reports of low specificity and high indeterminate study rates, particularly when used in obese patients and patients early in the course of their disease, or when performed by sonographers with limited experience.

OBJECTIVE

To (1) assess the impact of patient factors (gender, age, body mass index, and symptom duration) and system factors (call status or year of exam) on pediatric appendiceal US accuracy and indeterminate study rate, (2) assess the impact of indeterminate study results on follow-up CT and negative laparotomy rates and (3) present strategies to reduce the rate of indeterminate US studies and improve accuracy.

MATERIALS AND METHODS

We retrospectively reviewed all US reports performed for the assessment of acute appendicitis in children <18 years old at Mayo Clinic Rochester from January 2010 to June 2014.

RESULTS

A total of 790 US examinations were performed in 452 girls (57%) and 338 boys (43%). The prevalence of appendicitis was 18.5% (146/790). There were 109 true-positive, 440 true-negative, 17 false-positive, 6 false-negative, 218 equivocal and 41 technically inadequate US studies. A definitive interpretation was made in 72% of the studies, with an accuracy, sensitivity and specificity of 0.960, 0.948 and 0.963, respectively. No patient or system factors significantly affected US accuracy. Indeterminate studies (28%) had significantly higher CT utilization (46% vs. 11%) and normal appendectomy rates (6.9% vs. 3.5%).

CONCLUSION

US should be the initial imaging study of choice for pediatric appendicitis. When a definitive interpretation was given, the accuracy was 96%, was independent of patient and system factors and resulted in reduced follow-up CTs and negative laparotomies. Accuracy can be increased by requiring the presence of periappendiceal inflammatory changes prior to interpreting a mildly distended appendix as positive for acute appendicitis. The indeterminate study rate can be reduced by not requiring visualization of the normal appendix for the exclusion of acute appendicitis.