MRI effective for the assessment of acute appendicitis in pregnancy [Classics Series]

This study summary is an excerpt from the book 2 Minute Medicine’s The Classics in Medicine: Summaries of the Landmark Trials

1. In pregnant patients with suspected acute appendicitis and equivocal abdominal ultrasound, magnetic resonance imaging (MRI) demonstrated high accuracy, sensitivity, and negative predictive value for acute appendicitis.

Original Date of Publication: March 2006

Study Rundown: Acute appendicitis is a common cause of lower abdominal pain during pregnancy, with an incidence of 1 case per 1500 pregnancies. Ultrasonography is the initial imaging modality of choice to evaluate patients with acute right lower quadrant pain in pregnancy. However, due to the anatomical changes associated with the large gravid uterus, the sensitivity and specificity of identifying the appendix on ultrasonography is significantly lower compared to the general population. In cases of an equivocal ultrasound examination, MRI may be used to assess the appendix while avoiding ionizing radiation. The purpose of this landmark retrospective cohort was to determine the accuracy of MRI in the assessment of acute appendicitis during pregnancy. This trial retrospectively reviewed 51 consecutive pregnant patients who were clinically suspected of having acute appendicitis that underwent MRI examinations of the abdomen with oral contrast. Positive appendicitis findings included a dilated appendix with high-signal intensity luminal fluid on T2-weigted imaging or periappendiceal fat stranding. At the conclusion of the trial, MRI demonstrated positive findings in all four patients that had confirmed acute appendicitis. No cases of appendicitis were missed by MRI. Additionally, in patients with no appendicitis, MRI demonstrated an alternate diagnosis for acute abdominal pain in 25% of patients.  This study was the one of the first to demonstrate the high accuracy and negative predictive value to rule-out acute appendicitis in pregnant patients and highlighted the value of MRI in detecting periappendiceal findings as well as other potential etiologies of acute abdomen pain in pregnancy. Limitations included a small sample size and the fact that cases in which the appendix could not be visualized (16% of all patients) were classified as true negatives for statistical calculations rather than indeterminate. A number of other small retrospective reviews by Cobben et al., Brichard et al., and Israel et al., have confirmed the accuracy of MRI to be able to visualize the appendix in addition to determining other potential causes of acute abdominal pain.

Click to read the study in Radiology

In-Depth [Retrospective cohort]: This study reviewed 51 consecutive pregnant patients (mean age: 28.3 years; range: 15-37, mean gestational age: 19.8 weeks; range: 4-38 weeks) that underwent oral-contrast enhanced MRI imaging of the abdomen for assessment of acute appendicitis in a single institution in the United States. 94% (48/51) of patients had ultrasound prior to MRI examination. All MRI examinations were performed on a 1.5-T coil with T1- T2-, Half-Fournier single-shot fast spin echo, and transverse time-of-flight gradient echo sequences. Interpretation of a positive finding of acute appendicitis was based on the presence of a dilated (>7 mm in diameter) appendix with high signal intensity luminal fluid on T2-weight images. Positive appendicitis was also noted if periappendiceal fat stranding was observed.  The primary outcome was the accuracy, sensitivity, specificity, as well as positive and negative predictive values for appendicitis. At the conclusion of the study, MRI imaging demonstrated positive findings of appendicitis in all four cases with three inconclusive cases. All four patients with positive MRI findings had pathologically or CT-confirmed acute appendicitis. The appendix could not be visualized in 8 of the remaining 47 patients (17%) without acute appendicitis. As the study classified these nonvisualized cases as negatives rather than indeterminate, this translated into a prevalence-adjusted accuracy of 94% and a sensitivity, specificity, and negative predictive value of 100%, 93.6%, and 100%, respectively. Additionally, in patients with no evidence of acute appendicitis, MRI imaging provided an additional 58 alternative diagnoses related to the patient’s acute abdominal pain, including an enlarged right gonadal vein (n=11), right hydronephrosis (n=25), degenerated fibroids (n=6), and sub-chorionic hemorrhage (n=11).

Pedrosa I, Levine D, Eyvazzadeh AD, Siewert B, Ngo L, Rofsky NM. MR Imaging Evaluation of Acute Appendicitis in Pregnancy. Radiology. 2006 Mar 1;238(3):891–9.

Additional Review:

Cobben LP, Groot I, Haans L, Blickman JG, Puylaert J. MRI for Clinically Suspected Appendicitis During Pregnancy. Am J Roentgenol. 2004 Sep 1;183(3):671–5.  

Birchard KR, Brown MA, Hyslop WB, Firat Z, Semelka RC. MRI of Acute Abdominal and Pelvic Pain in Pregnant Patients. Am J Roentgenol. 2005 Feb 1;184(2):452–8.

Israel GM, Malguria N, McCarthy S, Copel J, Weinreb J. MRI versus ultrasound for suspected appendicitis during pregnancy. J Magn Reson Imaging. 2008 Aug 1;28(2):428–33.

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