Optimizing imaging in suspected appendicitis (OPTIMAP-study): a multicenter diagnostic accuracy study of MRI in patients with suspected acute appendicitis. Study Protocol

Magnetic Resonance Imaging Versus Ultrasound as the Initial Imaging Modality for Pediatric and Young Adult Patients With Suspected Appendicitis

BACKGROUND

While ultrasound (US), given its lack of ionizing radiation, is currently the recommended initial imaging study of choice for the diagnosis of appendicitis in pediatric and young adult patients, it does have significant shortcomings. US is time-intensive and operator dependent and results in frequent inconclusive studies, thus necessitating further imaging and admission for observation or repeat clinical visits. A rapid focused magnetic resonance imaging (MRI) for appendicitis has been shown to have definitive sensitivity and specificity, similar to computed tomography but without radiation and offers a potential alternative to US.

OBJECTIVE

In this single-center prospective cohort study, we sought to determine the difference in total length of stay and charges between rapid MRI and US as the initial imaging modality in pediatric and young adult patients presenting to the emergency department (ED) with suspected appendicitis. We hypothesized that rapid MRI would be more efficient and cost-effective than US as the initial imaging modality in the ED diagnosis of appendicitis.

METHODS

A prospective randomized cohort study of consecutive patients was conducted in patients 2 to 30 years of age in an academic ED with access to both rapid MRI and US imaging modalities 24/7. Prior to the start of the study, the days of the week were randomized to either rapid MRI or US as the initial imaging modality. Physicians evaluated patients with suspected appendicitis per their usual manner. If the physician decided to obtain radiologic imaging, the predetermined imaging modality for the day of the week was used. All decisions regarding other diagnostic testing and/or further imaging were left to the physician's discretion. Time intervals (minutes) between triage, order placement, start of imaging, end of imaging, image result, and disposition (discharge vs. admission), as well as total charges (diagnostic testing, imaging, and repeat ED visits) were recorded.

RESULTS

Over a 100-day period, 82 patients were imaged to evaluate for appendicitis; 45 of 82 (55%) of patients were in the US-first group, and 37 of 82 (45%) patients were in the rapid MRI-first group. There were no differences in patient demographics or clinical characteristics between the groups and no cases of missed appendicitis in either group. Eleven of 45 (24%) of US-first patients had inconclusive studies, resulting in follow-up rapid MRI and five return ED visits contrasted with no inconclusive studies or return visits (p < 0.05) in the rapid MRI group. The rapid MRI compared to US group was associated with longer ED length of stay (mean difference = 100 minutes; 95% confidence interval [CI] = 35-169 minutes) and increased ED charges (mean difference = $4,887; 95% CI = $1,821-$8,513).

CONCLUSIONS

In the diagnosis of appendicitis, US-first imaging is more time-efficient and less costly than rapid MRI despite inconclusive studies after US imaging. Unless the process of obtaining a rapid MRI becomes more efficient and less expensive, US should be the first-line imaging modality for appendicitis in patients 2 to 30 years of age.

An Imaging Diagnostic Protocol in Children with Clinically Suspected Acute Appendicitis

The objective of the present study is to evaluate a new diagnostic strategy using clinical findings followed by ultrasound (US) and, in selected cases, MRI. This study included 166 children presenting signs and symptoms suggesting acute appendicitis. Cases classified as suggesting appendicitis according to clinical exams had to be referred to surgery, whereas the other cases were discharged. Unclear cases were evaluated using US. If the US results were considered inconclusive, patients underwent MRI. Of the 166 patients, 78 (47%) had acute appendicitis and 88 (53%) had other diseases. The strategy under study had a sensitivity of 96 per cent, specificity of 100 per cent, positive predictive value of 100 per cent, negative predictive value of 97 per cent, and accuracy of 98 per cent. Eight patients remained undiagnosed and underwent MRI. After MRI two girls presented normal appendixes and were discharged. One girl had an enlarged appendix on MRI and appendicitis could have been confirmed by surgery. In the other five patients, no other sign of the disease was detected by MRI such as an inflammatory mass, free fluid or an abscess in the right iliac fossa. All of them were discharged after clinical observation. In the vast majority of cases the correct diagnosis was reached by clinical and US examinations. When clinical assessment and US findings were inconclusive, MRI was useful to detect normal and abnormal appendixes and valuable to rule out other abdominal pathologies that mimic appendicitis.

Accuracy of White Blood Cell Count and C-reactive Protein Levels Related to Duration of Symptoms in Patients Suspected of Acute Appendicitis

OBJECTIVES

Low levels of white blood cell (WBC) count and C-reactive protein (CRP) have been suggested to sufficiently rule out acute appendicitis. The diagnostic value of these tests is likely to depend on the duration of complaints. The aim of this study was to evaluate the accuracy of these inflammatory markers in relation to duration of symptoms in patients suspected of acute appendicitis.

METHODS

Patients suspected of having acute appendicitis were retrospectively selected from five prospective cohorts of patients with acute abdominal pain presenting at the emergency department (ED) in two European countries. Only adult patients with clinical suspicion of acute appendicitis based on medical history, physical examination, and laboratory studies at the time of registration in the original cohorts were included in this analysis. WBC count and CRP level were determined in all patients and a final diagnosis was assigned to every patient by an expert panel based on all available clinical data and follow-up. For categories based on symptom duration, the diagnostic accuracy of single and combined cutoff values was determined, and negative predictive values (NPV) and positive predictive values (PPV) were calculated. Subgroup analyses for age (<40 years or ≥40 years) and sex were performed.

RESULTS

A total of 1,024 patients with clinically suspected acute appendicitis were included, of whom 580 (57%) were assigned a final diagnosis of appendicitis. No value of WBC count, CRP level, or their combination resulted in a NPV of more than 90%, regardless of the duration of symptoms. A WBC count of >20 × 10(9) /L in combination with symptoms for more than 48 hours was associated with a PPV of 100%. However, only eight of the 1,024 patients (1%) fulfilled these criteria, limiting the clinical applicability. No other cutoff level of WBC count, CRP level, or their combination resulted in a PPV of more than 80%, regardless of the duration of symptoms. In female patients, normal levels of CRP and WBC count more accurately excluded the diagnosis of appendicitis than normal levels did in male patients.

CONCLUSIONS

No WBC count or CRP level can safely and sufficiently confirm or exclude the suspected diagnosis of acute appendicitis in patients who present with abdominal pain of 5 days or less in duration.

Scoring system to distinguish uncomplicated from complicated acute appendicitis

Background

Non-operative management may be an alternative for uncomplicated appendicitis, but preoperative distinction between uncomplicated and complicated disease is challenging. This study aimed to develop a scoring system based on clinical and imaging features to distinguish uncomplicated from complicated appendicitis.

Methods

Patients with suspected acute appendicitis based on clinical evaluation and imaging were selected from two prospective multicentre diagnostic accuracy studies (OPTIMA and OPTIMAP). Features associated with complicated appendicitis were included in multivariable logistic regression analyses. Separate models were developed for CT and ultrasound imaging, internally validated and transformed into scoring systems.

Results

A total of 395 patients with suspected acute appendicitis based on clinical evaluation and imaging were identified, of whom 110 (27·8 per cent) had complicated appendicitis, 239 (60·5 per cent) had uncomplicated appendicitis and 46 (11·6 per cent) had an alternative disease. CT was positive for appendicitis in 284 patients, and ultrasound imaging in 312. Based on clinical and CT features, a model was created including age, body temperature, duration of symptoms, white blood cell count, C-reactive protein level, and presence of extraluminal free air, periappendiceal fluid and appendicolith. A scoring system was constructed, with a maximum possible score of 22 points. Of the 284 patients, 150 had a score of 6 points or less, of whom eight (5·3 per cent) had complicated appendicitis, giving a negative predictive value (NPV) of 94·7 per cent. The model based on ultrasound imaging included the same predictors except for extraluminal free air. The ultrasound score (maximum 19 points) was calculated for 312 patients; 105 had a score of 5 or less, of whom three (2·9 per cent) had complicated appendicitis, giving a NPV of 97·1 per cent.

Conclusion

With use of novel scoring systems combining clinical and imaging features, 95 per cent of the patients deemed to have uncomplicated appendicitis were correctly identified as such. The score can aid in selection for non-operative management in clinical trials.

Prospective evaluation of the added value of imaging within the Dutch National Diagnostic Appendicitis Guideline--do we forget our clinical eye?

BACKGROUND

Annually 16,000 appendectomies are performed in the Netherlands, of which 15-20% are negative. In 2010, to reduce this unacceptable percentage of superfluous appendectomies, the Dutch Association for Surgery introduced the 'Appendicitis Guideline'. This guideline recommends the use of imaging. In this observational prospective study the added value of imaging in everyday clinical practice is evaluated.

METHODS

All patients with suspected appendicitis were included at the emergency department of a Dutch teaching hospital during the period from September 2011 to May 2012 (n = 350; 237 adults and 113 children under 18 years). Adherence to the guideline was evaluated.

RESULTS

75 Patients (21%) were not referred for imaging because of a low suspicion or alternative diagnosis. In 16 patients (5%) the guideline was not followed. Of the 259 patients (74%) who underwent ultrasonography, 105 (30%) also underwent computed tomography (CT). 127 appendectomies were performed, showing appendicitis in 112 patients (88%); 15 appendectomies (12%) were negative. In the latter group, 12 were performed after false positive imaging results, and 3 following inconclusive imaging results.

CONCLUSION

When using imaging in the diagnosis of appendicitis, the percentage of negative appendectomies remains close to the percentage declared as unacceptable by the publishers of the guideline.

Imaging for appendicitis: should radiation-induced cancer risks affect modality selection?

PURPOSE

To compare life expectancy (LE) losses attributable to three imaging strategies for appendicitis in adults-computed tomography (CT), ultrasonography (US) followed by CT for negative or indeterminate US results, and magnetic resonance (MR) imaging-by using a decision-analytic model.

MATERIALS AND METHODS

In this model, for each imaging strategy, LE losses for 20-, 40-, and 65-year-old men and women were computed as a function of five key variables: baseline cohort LE, test performance, surgical mortality, risk of death from delayed diagnosis (missed appendicitis), and LE loss attributable to radiation-induced cancer death. Appendicitis prevalence, test performance, mortality rates from surgery and missed appendicitis, and radiation doses from CT were elicited from the published literature and institutional data. LE loss attributable to radiation exposure was projected by using a separate organ-specific model that accounted for anatomic coverage during a typical abdominopelvic CT examination. One- and two-way sensitivity analyses were performed to evaluate effects of model input variability on results.

RESULTS

Outcomes across imaging strategies differed minimally-for example, for 20-year-old men, corresponding LE losses were 5.8 days (MR imaging), 6.8 days (combined US and CT), and 8.2 days (CT). This order was sensitive to differences in test performance but was insensitive to variation in radiation-induced cancer deaths. For example, in the same cohort, MR imaging sensitivity had to be 91% at minimum (if specificity were 100%), and MR imaging specificity had to be 62% at minimum (if sensitivity were 100%) to incur the least LE loss. Conversely, LE loss attributable to radiation exposure would need to decrease by 74-fold for combined US and CT, instead of MR imaging, to incur the least LE loss.

CONCLUSION

The specific imaging strategy used to diagnose appendicitis minimally affects outcomes. Paradigm shifts to MR imaging owing to concerns over radiation should be considered only if MR imaging test performance is very high.

A simple clinical decision rule to rule out appendicitis in patients with nondiagnostic ultrasound results

OBJECTIVES

The objective was to identify a set of clinical features that can rule out appendicitis in patients with suspected acute appendicitis and nondiagnostic ultrasound (US) results, allowing safe discharge and next-day reevaluation without initial computed tomography (CT) or magnetic resonance imaging (MRI).

METHODS

Data on clinical and US evaluation, including a number of prespecified variables potentially associated with acute appendicitis, were prospectively collected in two diagnostic accuracy studies of imaging. These studies included patients with suspected appendicitis seen in the emergency department (ED). For development and validation of the clinical decision rule (CDR), only patients with inconclusive or negative US results were included. There were 199 (of 422) patients in the development cohorts and 120 (of 211) patients in the validation cohort. Logistic regression analysis was used for data from patients with inconclusive or negative US results, and profiles were created of all possible combinations of predictors retained in the multivariable model. A final diagnosis was assigned by an expert panel based on perioperative data, histopathology, and clinical follow-up of at least 3 months.

RESULTS

The CDR selected patients after negative or inconclusive US for discharge and next-day reevaluation without initial CT or MRI if fewer than two of the following predictors were present: male sex, migration of pain to the right lower quadrant, vomiting, and white blood cell (WBC) count higher than 12.0 × 10(9) /L. Applying the CDR in the development set selected 126 of 199 (63%) patients with negative or inconclusive US results for discharge without further imaging. This rule reduced the probability of appendicitis from 26% (51 of 199) in the total group of patients with negative or inconclusive US results to 12% (15 of 126) in the group that would be discharged based on the rule (p = 0.001). In the validation set (n = 120), the decision rule selected 72 (60%) patients for discharge and next-day reevaluation and reduced the probability of appendicitis from 20% (24 of 120) in the total group to 6% (4 of 72) in the patients selected on the rule (p = 0.001). The negative predictive value of the decision rule in the validation set was 94% (95% confidence interval [CI] = 87% to 98%). In comparison, the negative predictive value of CT in the same group was 99% (95% CI = 93% to 100%, p = 0.14), and that of MRI was 99% (95% CI = 94% to 100%, p = 0.12). Alternative decision rules based on combinations of the present decision rule with C-reactive protein (CRP) results did not improve selection.

CONCLUSIONS

This newly developed CDR significantly reduces the probability of appendicitis in a large subgroup of patients with negative or inconclusive US results. These patients can be safely discharged for outpatient reevaluation without further initial imaging if proper follow-up is available. This could assist in lowering the number of ED imaging investigations in patients with suspected appendicitis.

Accuracy of MRI compared with ultrasound imaging and selective use of CT to discriminate simple from perforated appendicitis

BACKGROUND

Discrimination between simple and perforated appendicitis in patients with suspected appendicitis may help to determine the therapy, timing of surgery and risk of complications. The aim of this study was to estimate the accuracy of magnetic resonance imaging (MRI) in distinguishing between simple and perforated appendicitis, and to compare MRI against ultrasound imaging with selected additional (conditional) use of computed tomography (CT).

METHODS

Patients with clinically suspected appendicitis were identified prospectively at the emergency department of six hospitals. Consenting patients underwent MRI, but were managed based on findings at ultrasonography and conditional CT. Radiologists who evaluated the MRI were blinded to the results of ultrasound imaging and CT. The presence of perforated appendicitis was recorded after each evaluation. The final diagnosis was assigned by an expert panel based on perioperative data, histopathology and clinical follow-up after 3 months.

RESULTS

MRI was performed in 223 of 230 included patients. Acute appendicitis was the final diagnosis in 118 of 230 patients, of whom 87 had simple and 31 perforated appendicitis. MRI correctly identified 17 of 30 patients with perforated appendicitis (sensitivity 57 (95 per cent confidence interval 39 to 73) per cent), whereas ultrasound imaging with conditional CT identified 15 of 31 (sensitivity 48 (32 to 65) per cent) (P = 0.517). All missed diagnoses of perforated appendicitis were identified as simple acute appendicitis with both imaging protocols. None of the MRI features for perforated appendicitis had a positive predictive value higher than 53 per cent.

CONCLUSION

MRI is comparable to ultrasonography with conditional use of CT in identifying perforated appendicitis. However, both strategies incorrectly classify up to half of all patients with perforated appendicitis as having simple appendicitis. Triage of appendicitis based on imaging for conservative treatment is inaccurate and may be considered unsafe for decision-making. Presented to a scientific meeting of the Association of Surgeons of the Netherlands, Veldhoven, The Netherlands, May 2012; published in abstract form as Br J Surg 2012; 99(Suppl 7): S6.

MRI features associated with acute appendicitis

OBJECTIVES

To identify MRI features associated with appendicitis.

METHODS

Features expected to be associated with appendicitis were recorded in consensus by two expert radiologists on 223 abdominal MRIs in patients with suspected appendicitis. Nine MRI features were studied: appendix diameter >7 mm, appendicolith, peri-appendiceal fat infiltration, peri-appendiceal fluid, absence of gas in the appendix, appendiceal wall destruction, restricted diffusion of the appendiceal wall, lumen or focal fluid collections. Appendicitis was assigned as the final diagnosis in 117/223 patients. Associations between imaging features and appendicitis were evaluated with logistic regression analysis.

RESULTS

All investigated features were significantly associated with appendicitis in univariate analysis. Combinations of two and three features were associated with a probability of appendicitis of 88 % and 92 %, respectively. In patients without any of the nine features, appendicitis was present in 2 % of cases. After multivariate analysis, only an appendix diameter >7 mm, peri-appendiceal fat infiltration and restricted diffusion of the appendiceal wall were significantly associated with appendicitis. The probability of appendicitis was 96 % in their presence and 2 % in their absence.

CONCLUSIONS

An appendix diameter >7 mm, peri-appendiceal fat infiltration and restricted diffusion of the appendiceal wall have the strongest association with appendicitis on MRI.

KEY POINTS

• An enlarged appendix, fat infiltration and restricted diffusion are associated with appendicitis. • One such feature on MRI gives an 88 % probability of appendicitis. • Two features in combination give a probability of appendicitis of 94 %. • Combinations of three features give a probability of appendicitis of 96 %. • The absence of these features almost rules out appendicitis (2 %).

Comparison of imaging strategies with conditional contrast-enhanced CT and unenhanced MR imaging in patients suspected of having appendicitis: a multicenter diagnostic performance study

PURPOSE

To compare the diagnostic performance of imaging strategies with magnetic resonance (MR) imaging and computed tomographic (CT) imaging in adult patients suspected of having appendicitis.

MATERIALS AND METHODS

Institutional review board approval was obtained prior to study initiation, and patients gave written informed consent. In a multicenter diagnostic performance study, adults suspected of having appendicitis were prospectively identified in the emergency department. Consenting patients underwent ultrasonography (US) and subsequent contrast-enhanced CT if US imaging yielded negative or inconclusive results. Additionally, all patients underwent unenhanced MR imaging, with the reader blinded to other findings. An expert panel assigned final diagnosis after 3 months. Diagnostic performance of three imaging strategies was evaluated: conditional CT after US, conditional MR imaging after US, and immediate MR imaging. Sensitivity and specificity were calculated by comparing findings with final diagnosis.

RESULTS

Between March and September 2010, 229 US, 115 CT, and 223 MR examinations were performed in 230 patients (median age, 35 years; 40% men). Appendicitis was the final diagnosis in 118 cases. Conditional and immediate MR imaging had sensitivity and specificity comparable to that of conditional CT, which resulted in 3% (three of 118; 95% confidence interval [CI]: 1%, 7%) missed appendicitis, and 8% (10 of 125; 95% CI: 4%, 14%) false-positives. Conditional MR missed appendicitis in 2% (two of 118; 95% CI: 0%, 6%) and generated 10% (13 of 129; 95% CI: 6%, 16%) false-positives. Immediate MR missed 3% (four of 117; 95% CI: 1%, 8%) appendicitis with 6% (seven of 120; 95% CI: 3%, 12%) false-positives. Conditional strategies resulted in more false-positives in women than in men (conditional CT, 17% vs 0%; P = .03; conditional MR, 19% vs 1%; P = .04), wherease immediate MR imaging did not.

CONCLUSION

The accuracy of conditional or immediate MR imaging was similar to that of conditional CT in patients suspected of having appendicitis, which implied that strategies with MR imaging may replace conditional CT for appendicitis detection.

On the Role of Ultrasonography and CT Scan in the Diagnosis of Acute Appendicitis

The purposes of this study were to revisit the utility of ultrasonography (USG) as a primary imaging modality in acute appendicitis (AA) and to establish the role of CT scan as a second-line/problem-solving modality. All cases of suspected AA were referred for urgent USG. USG was done with standard protocol for appendicitis. Limited computed tomographic (CT) scan [NCCT ± CECT (IV contrast only)] was done for the lower abdomen and pelvis where sonographic findings were equivocal. One hundred and twenty-one patients were referred for USG for suspected appendicitis. Eight-four patients underwent surgery for AA based on clinical as well as imaging findings, of whom 76 had appendicitis confirmed at histopathology. Three patients were misdiagnosed (3.6 %) on USG as appendicitis. Of 76 patients of appendicitis confirmed histopathologically, 63 (82.8 %) had features of appendicitis on USG and did not require any additional imaging modality. Of 121 patients, 12 (10 %) needed CT scan because of atypical features on USG. Of these 12 patients, seven had retrocecal appendicitis, and three high-up paracolic appendicitis. USG alone had sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy of 81, 88, 92.6, 71.6, and 83 %, respectively. When combined with CT scan in select cases, the sensitivity, specificity, PPV, NPV, and accuracy of combined USG + CT scan were 96 % (P = 0.0014), 89 %, 93 %, 93.5 % (P = 0.0001), and 93 % (P = 0.0484), respectively. Twenty-eight (23 %) patients were given alternative diagnosis on USG. Dedicated appendiceal USG should be used as a primary imaging modality in diagnosing or excluding AA. Appendiceal CT can serve as a problem-solving modality.

An evaluation of a superfast MRI sequence in the diagnosis of suspected acute appendicitis

BACKGROUND

A lack of typical symptoms in acute appendicitis may delay the appropriate therapy. We hypothesized that a superfast MRI sequence with fat suppression could assist in the diagnosis of acute appendicitis.

OBJECTIVE

To evaluate the sensitivity and specificity of MRI in the diagnosis of suspected acute appendicitis especially in the early stages and before surgery.

METHODS

Subject images were acquired with a 1.5-T clinical MRI scanner (Achieva Nova Dual, Philips, Netherlands) with a four-element phased array abdominal coil with a SENSE factor of 1.8. A total of 41 cases with suspected acute appendicitis were recruited. SENSE-BTFE-SPIR sequence, sensitivity encoding (SENSE) with balanced turbo field echo (BTFE) and spectral presaturation and inversion recovery (SPIR), was adopted in this study.

RESULTS

The sensitivity and specificity were 91.7% and 100%, respectively, in the diagnosis of acute appendicitis by SENSE-BTFE-SPIR in this series. Cases with simple acute appendicitis showed a higher T2 signal in the appendiceal wall, with local fluid surrounding appendix. Cases with purulent appendicitis showed an increased T2 signal within the cavity of the appendix, along with appendiceal wall thickening, or increased T2 signals around effusions in cases with gangrenous appendicitis. A periappendiceal abscess showed a localized, high-signal fluid collection that may have had extensive effects on the adjacent bowel loops, into which the entire appendix may disappear.

CONCLUSIONS

The fast SENSE-BTFE-SPIR sequence is capable of demonstrating the location and position of the appendix, the presence of acute appendicitis and its complications, and the clinical stages.