Efficacy of MRI for the Accurate Diagnosis of Appendicitis in Pregnancy

BACKGROUND AND PURPOSE:

• Imaging for appendicitis in pregnancy
  • Ultrasound: Significant failure rate due to limited detection capability
  • CT: Used for inconclusive ultrasound results or MRI not available
    • Associated with: Ionizing radiation | Possible allergic reactions to contrast dye
  • MRI: ACR recommended technique for the diagnosis of appendicitis in pregnancy
• Kave et al. (World Journal of Emergency Surgery, 2019) assessed the efficacy of MRI for the diagnosis of acute appendicitis during pregnancy

METHODS:

• Systematic review and meta-analysis
• Inclusion criteria
  • Retrospective and prospective blinded studies
  • Studies that investigated the performance of MRI for suspected appendicitis
• Data synthesis and analysis
  • Two independent researchers
  • Risk of bias of evaluated
  • Pooled measures: Sensitivity | Specificity | Diagnostic odds ratio (DOR) | Area under the curves (AUC)

RESULTS:

• 19 studies
• MRI performance shows high accuracy for detecting appendicitis in pregnancy
  • Sensitivity: 91.8% (95% CI, 87.7 to 94.9%)
  • Specificity: 97.9% (95% CI, 0.97.2 to 100%)
  • DOR: 177.60 (95% CI 35.012–900.91)
• This study supports MRI as the diagnostic imaging modality of choice due to lack of ionizing radiation and the authors further state

As radiologists become increasingly comfortable with interpreting abdominal and pelvic MRI, and as it becomes more widely available as an emergent procedure, its utility will continue to increase in the future

CONCLUSION:

• MRI has both high sensitivity and specificity for diagnosing acute appendicitis in pregnant women with suspected appendicitis

Learn More – Primary Sources:

Pregnancy and appendicitis: a systematic review and meta-analysis on the clinical use of MRI in diagnosis of appendicitis in pregnant women

Exposure to Ionizing Radiation During Pregnancy – What Now?

CLINICAL ACTIONS:

When considering the effects of ionizing radiation during pregnancy:

• Do not recommend termination solely on the basis of exposure to ionizing radiation
• Patients should be counseled and prenatal imaging performed for structural anomalies and growth restriction for exposure >50mGy
  • Radiation exposure through radiography, CT scan or nuclear imaging is usually at a dose that is lower than the threshold exposure associated with risk to the fetus and should not be withheld if necessary
• Ultrasound and MRI are not associated with fetal risk and are first line imaging modalities
  • Use ‘prudently’ and when the results will provide medical benefit
• Consult radiation physicist to calculate total dose, if multiple imaging studies were performed
  • The Health Physics Society (HPS) maintains an open access website with information for professionals and patients (see ‘Learn More – Primary Sources’ below)
• A 10-20 mGy fetal exposure may increase the background risk of leukemia by a factor of 1.5-2.0
• There is no risk to lactation from external sources of ionizing radiation

Interim ACOG Update (October 2017) Regarding Exposure to MRI and Gadolinium in Pregnancy

• Limit the use of gadolinium contrast with MRI
• Only use gadolinium contrast if it ‘significantly improves diagnostic performance’ and will improve maternal and/or fetal outcomes
• Breastfeeding should not be interrupted after use of gadolinium, consistent with ACR guidance
• A recent retrospective cohort study by Ray et al. (JAMA, 2016) comparing gadolinium MRI (n = 397) at any time during pregnancy with no MRI (n = 1,418,451), demonstrated
  • The risk of any rheumatological, inflammatory, or infiltrative skin condition in offspring was increased (adjusted hazard ratio (HR) 1.36; 95% CI, 1.09 to 1.69)
  • Stillbirths and neonatal deaths (within 28 days of birth) were increased (adjusted relative risk 3.70; 95% CI, 1.55 to 8.85) for an adjusted risk difference of 47.5 per 1000 pregnancies (95% CI, 9.7 to 138.2)

SYNOPSIS:

X-ray procedures may be indicated during pregnancy or may occur inadvertently before the pregnancy is diagnosed. The risk to a fetus from ionizing radiation is dependent on the gestational age at the time of the exposure and the dose of radiation. Growth restriction, microcephaly and intellectual disability are the most common adverse effects from high dose radiation exposure. They have not been reported with radiation exposure less than 50 mGy.  Actual fetal doses are dependent on gestational age, maternal body habitus and acquisition parameters.

KEY POINTS:

Fetal Dose for common radiologic exams

• Chest X-ray, two views generally: 0.0005-0.01 mGy
• Abdominal radiography: 0.1-3 mGy
• IVP: 5-10 mGy
• Double contrast barium enema: 1.0-20 mGy
• Head or neck CT: 1.0-10 mGy
• Chest CT or CT pulmonary angiography: 0.01-0.66 mGy
• Abdominal CT: 1.3-35 mGy

‘All or None’ Effect

• Before implantation (0 to 2 weeks after fertilization)
  • Death of embryo or no consequence
  • Estimated threshold: 50-100 mGy

Learn More – Primary Sources:

ACOG Committee Opinion 723: Guidelines for Diagnostic Imaging During Pregnancy and Lactation

JAMA: Association Between MRI Exposure During Pregnancy and Fetal and Childhood Outcomes

HPS: Radiation & Reproduction

HPS: Pregnancy and Radiation Exposure – Patient FAQs

ACR Manual on Contrast Media