Rationale and Objectives
Perform a meta-analysis evaluating the diagnostic performance of magnetic resonance imaging (MRI) for the diagnosis of acute appendicitis.
Materials and Methods
MEDLINE and EMBASE were queried between January 1995 and December 2009. Prospective and retrospective studies were included if they: used MRI as a diagnostic test for appendicitis, used pathology or clinical follow-up as the reference standard, and reported absolute number of true-positive, true-negative, false-positive, and false-negative results, or stated sufficient data to derive these values. Summary sensitivity, summary specificity, positive and negative likelihood ratios (LR+) and (LR-), and diagnostic odds ratio were calculated. Heterogeneity of the results was assessed using Forest plots and the value of inconsistency index (I 2 ).
Results
The inclusion criteria were fulfilled by eight articles with a total of 363 patients (mean age 26.9 ± 7.2 years; 86.2 % female). The appendix was not found in eight patients, with one article not reporting such data. The summary sensitivity was 97% (92%–99% at 95% confidence interval [CI]) and summary specificity was 95% (CI: 94%–99%), with a LR+ of 16.3 (CI: 9.1–29.1) and a LR- of 0.09 (CI: 0.04–0.197). Diagnostic odds ratio was 299.85 (CI: 97.5–921.61). No heterogeneity was found in the sensitivity (I 2 = 0.0, P = .4589). Minimal heterogeneity was found in the specificity (I 2 = 21.9%, P = .2553).
Conclusion
MRI appears promising in the evaluation of acute appendicitis, although larger future studies are warranted to confirm the results.
Acute appendicitis is a common etiology for acute abdominal pain and the need for emergent surgery. Although clinical and laboratory correlation may be enough for diagnosis, more clinicians are relying on radiological evaluation of the abdomen to make a definitive diagnosis . Additionally, up to one third of patients with appendicitis present with atypical symptoms that complicate a clinical diagnosis of appendicitis . Additionally, certain laboratory parameters may mire clinical diagnosis, such as physiologic leukocytosis of pregnancy . These dilemmas can potentially lead to unnecessary surgical intervention, thus more clinicians are using radiological evaluation for a definitive diagnosis .
Computed tomography (CT) is an established radiological procedure for the evaluation of acute appendicitis, but exposes the patient to ionizing radiation . With rising concerns of the public and medical communities with regard to increasing number of studies leading to increasing ionizing radiation exposure, alternative modalities have been investigated as potential diagnostic tools. This is especially true for pregnant patients, for whom acute appendicitis is the most common cause of acute abdomen and there are special considerations to avoid ionizing radiation. .
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Materials and methods
Execution of Data Collection and Statistical Analysis
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Data Sources and Searches
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Study Selection
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Data Extraction and Quality Assessment
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Data Synthesis and Statistical Analysis
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LR+=sensitivity/(1−specificity) LR
+
=
sensitivity
/
(
1
-
specificity
)
LR−=(1−sensitivity)/specificity LR
-
=
(
1
-
sensitivity
)
/
specificity
A LR+ >10 and a LR- <0.1 implies a large and often conclusive increase or decrease in the likelihood of disease, respectively.
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dOR=LR+/LR− dOR
=
LR
+
/
LR
-
The dOR ranges from 0 to infinity. The higher the value, the better the test is at discriminating between those with and without the disease. A value of 1 is indicative of no discrimination. A value less than 1 indicates tests were interpreted poorly (more negative tests among those with disease).
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I2=100[(Q−df)/Q] I
2
=
100
[
(
Q
-
df
)
/
Q
]
where Q is Cochran’s heterogeneity statistic and df is the degrees of freedom. A value of 0% indicates no heterogeneity and any value greater than 50% may be considered significant heterogeneity. Overall prevalence of appendicitis in the studies that met inclusion criterion was also calculated.
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Results
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Table 1
Characteristics of Study Populations
First Author Journal (Year) Total Number of Patients ( n ) Number Female Mean Age (y) Scanner Brand and Strength (T) MRI Sequences Oto_Abdom. Imaging_ (2008) 118 118/118 26.9 General Electric (1.5) T2 FS; T2 SS FSE; STIR; T1 FSE; T1 GRE Cobben_Am J Roentgenol AJR_ (2004) 12 12/12 28 Siemens (1.0) T1 FLAS; T2 TSE; T2 TSE FS Incesu_Am J Roentgenol AJR_ (1997) 60 33/60 20 GE (0.5) T2 FSE, T1 SE; T2 FSE FS; T1 SE gad FS Birchard_Am J Roentgenol AJR_ (2005) 29 29/29 25 Siemens (1.5) T1 spoiled GRE; T2 HASTE; gad spoiled GRE Oto_Radiology_ (2005) 23 23/23 24.7 GE (1.5) T2 FSE; T2 FSE FS; STIR; T1 FSE Nitta_J. Magn. Reson. Imaging_ (2005) 27 14/27 37.1 Philips (0.5) T1 SE; T2 FSE; T2 FSE FS Pedrosa_Radiology_ (2006) 51 51/51 28.2 Siemens or GE (1.5) Oral ferumoxsil and barium sulfate for all; HF SS FSE; TOF T2 ∗ GRE; T1 IP/OP Israel_J. Magn. Reson. Imaging_ (2008) 33 33/33 25.6 GE (1.5) SS FSE; T2 FSE FS; T1
TSE, turbo spin echo; UTSE, ultra turbo spin echo; STIR, short tau inversion recovery; FLAS, fast low angle shot; FS, fat suppressed; gad, gadolinium enhanced; GRE, gradient recall echo; SS, single shot; TOF, time of flight; IP/OP, in phase/opposed phase; SE, spin echo; HF, half Fourier; HASTE, half Fourier single shot turbo spin echo; T, Tesla.
Table 2
Quality Assessment
First Author Item 1 Item 2 Item 3 Item 4 Item 5 Item 6 Item 7 Item 8 Item 9 Item 10 Score Oto ∗ Yes Yes Yes Yes No Yes Yes Yes Yes Yes 9 Cobben Yes No Yes No Yes Yes Yes Yes No Yes 7 Incesu Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes 10 Birchard Yes Yes No No Yes Yes Yes Yes No Yes 7 Oto Yes Yes Yes No No Yes Yes Yes No Yes 7 Nitta Yes Yes No No No Yes Yes No Yes Yes 6 Pedrosa Yes Yes Yes Yes No Yes Yes Yes Yes Yes 9 Israel Yes Yes No No No Yes Yes Yes No Yes 6
Item 1: Was the population clinically relevant, defined as a group of patients covering the spectrum of disease that is likely to be encountered in the current or future use of the test? Item 2: was there complete verification by the reference standard? Item 3: Was there blinded interpretation of the test results? Item 4: Was there consecutive patient selection? Item 5: Was there prospective enrollment of patients? Item 6: Was there adequate description and quality of the imaging procedure? Item 7: Was the quality of the reference test technically adequate? Item 8: Was there adequate clinical description of the patient population? Item 9: Was the sample size ≥35 patients? Item 10: Was there adequate reporting of results, including summary and subgrouping indexes of accuracy?
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Discussion
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Table 3
The Results from recent Meta-analyses in Diagnosing Acute Appendicitis using Magnetic Resonance Imaging, Computed Tomography, and/or Ultrasound
Authors Barger et al Doria et al ∗ van Randen et al Modality Magnetic resonance imaging Ultrasound Computed tomography Ultrasound Computed tomography Sensitivity 0.97 0.83 0.94 0.78 0.91 Specificity 0.97 0.93 0.94 0.83 0.90
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