Feature

MRI for Emergency Clinicians

Emergency Medicine. 2018 December;50(12):1-6

References

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MRI has high sensitivity and very high specificity for the diagnosis of appendicitis. Abnormal diagnostic findings include an appendiceal diameter > 7 mm and surrounding inflammatory changes.22 The low negative predictive value of MRI obviates the need for risky surgeries in pregnant patients in whom appendicitis is ruled out. MRI also allows for the diagnosis of other etiologies of abdominal pain in these patients.²¹

Pediatric patients with abdominal pain -concern for appendicitis (see the Cautions and Limitations section above on MRI in pediatric patients)

For pediatric patients with possible appendicitis, ultrasound is the first imaging modality of choice, followed by CT. However, ultrasound is operator dependent, with wide variability in its ability to correctly diagnose appendicitis, often leading to equivocal results. CT involves ionizing radiation exposure.²⁰ Non-contrast MRI is the emerging imaging modality for these patients. A systematic review of almost 2000 pediatric patients found MRI sensitivity and specificity to be 97% and 97% with a low negative appendectomy rate.²³

Cost and image acquisition time are limitations for MRI use for children. Pediatric patients may require sedation with long acquisition times in order to ensure that high-quality images are obtained, potentially introducing more associated costs and safety concerns. Shorter image-acquisition times would make MRI a more widely applicable test.²³

Orthopedics

Various orthopedic conditions can be investigated by MRI, but this is not commonly done in the ED. Acute knee trauma with a concern for ligamentous, cartilaginous, or meniscal injury is one example. The patient with a concern for occult fracture or injury to the shoulder, elbow, or scaphoid represent others.

However, the special case of the patient with hip trauma with negative radiographs who will not weight bear or has significant pain is worth considering. MRI to either diagnose or exclude occult hip, pelvic, or acetabular fracture is traditionally considered to be the criterion standard. However, a 2016 study called this widely-held belief into question. It found that CT and MRI were similarly sensitive and concluded that starting with CT was a reasonable approach.²⁴ MRI can be considered if the diagnosis remains in doubt.