What is the role of Magnetic Resonance Imaging (MRI) of the abdomen in diagnosing appendicitis in a pregnant patient?

From the Guidelines

Magnetic Resonance Imaging (MRI) of the abdomen plays a crucial role in diagnosing appendicitis in pregnant patients, particularly when ultrasound (US) results are equivocal or indeterminate.

Key Findings

• The sensitivity and specificity of initial MRI in pregnant people with suspected appendicitis are 0.93 (0.18-1.00) and 0.96 (0.54-1.00), respectively, as reported in 11 observational studies 1.
• A study of 51 pregnant patients who underwent MRI after inconclusive US showed an overall sensitivity of 100%, a specificity of 93.6%, and a prevalence-adjusted PPV and NPV of 1.4% and 100%, respectively 1.
• Another study of 49 pregnant patients found that MRI diagnosed all cases with acute appendicitis, with one case remaining inconclusive, and prevented surgery in 88% of patients 1.

Clinical Implications

• MRI abdomen and pelvis without IV contrast may be considered as a first imaging test in pregnant patients with suspected appendicitis, especially late in pregnancy 1.
• If a life-threatening diagnosis must be excluded and US and MRI abdomen and pelvis without IV contrast are inconclusive or nondiagnostic, MRI abdomen and pelvis with contrast could be considered 1.
• The T1 bright appendix sign, defined as a high-intensity signal filling more than half the length of the appendix on T1-weighted imaging, was shown to be a specific sign for a normal appendix in a retrospective study of 125 pregnant patients 1.

Limitations

• The evidence for all imaging recommendations was of very low certainty due to study risk of bias concerns and indirectness of comparisons 1.
• Inconsistent results and imprecision of results were also concerns for many of the imaging modalities studied 1.

From the Research

Role of MRI in Diagnosing Appendicitis in Pregnant Patients

• MRI is a valuable diagnostic tool for evaluating acute abdominal pain in pregnancy, particularly for diagnosing appendicitis 2, 3.
• The use of MRI in pregnant women is recommended due to its ability to identify the normal or inflamed appendix without exposing the patient to radiation 2, 4.
• MRI protocols for evaluating pregnant women with abdominal pain focus on the appearance and location of the normal and diseased appendix, and can help reduce the negative laparotomy rate in this patient population 3.

Diagnostic Accuracy of MRI

• Studies have shown that MRI has high sensitivity and specificity for diagnosing appendicitis in pregnant women, with summary sensitivity and specificity estimates of 0.96 and 0.97, respectively 4.
• The use of different MR pulse sequences, such as T1-weighted and T2-weighted sequences, can improve diagnostic accuracy, with T2-weighted sequences showing high sensitivity and specificity for diagnosing appendicitis 5.
• The addition of diffusion-weighted imaging (DWI) to MRI examinations can further improve diagnosis, with the MRI appendicitis scale being an objective and significant independent predictor of acute appendicitis in pregnant women 6.

Advantages of MRI in Pregnant Patients

• MRI does not expose patients to radiation, making it a safe and attractive imaging modality for pregnant women and children 2, 4.
• MRI can help identify other pathologic conditions that may masquerade as acute appendicitis in pregnant women, reducing the risk of misdiagnosis and unnecessary surgery 3.
• The use of MRI in pregnant women can help reduce the negative laparotomy rate and improve patient outcomes 3.