What MRI (Magnetic Resonance Imaging) should be ordered for a suspected aortic dissection?

MRI for Aortic Dissection: Diagnostic Approach

For suspected aortic dissection, MRA chest without and with IV contrast is the recommended MRI protocol, offering excellent sensitivity (92-98%) and specificity (100%) for diagnosing aortic dissection. 1

Optimal MRI Protocol Selection

• MRA chest without and with IV contrast is superior to non-contrast MRA for aortic dissection diagnosis, providing detailed visualization of the dissection flap, entry tears, and branch vessel involvement 1
• MRA demonstrates 100% sensitivity for identifying thrombus formation and pericardial effusion, which are critical complications of aortic dissection 1
• ECG-gated acquisition should be used to minimize cardiac motion artifacts and allow for accurate orthogonal measurement of the aortic dimensions 1
• When the dissection potentially extends beyond the thorax, imaging should include the abdomen and pelvis to evaluate the full extent of the disease 1

Advantages of MRA for Aortic Dissection

• MRA provides excellent visualization of the dissection extent, with the true lumen typically located anteriorly and the false lumen posteriorly 2
• MRA can accurately differentiate between true and false lumens, which is essential for treatment planning 2
• MRA avoids radiation exposure and iodinated contrast, making it suitable for patients with contrast allergies or renal insufficiency 3
• Advanced MRA techniques can quantify flow in both true and false lumens, providing hemodynamic information that may guide management 4

Clinical Considerations and Limitations

• MRA is often not immediately available in emergency settings, limiting its use in acute presentations 2
• CT angiography remains the first-line imaging modality for suspected aortic dissection due to its wider availability, speed, and comprehensive anatomic detail 5
• MRA is particularly valuable in specific clinical scenarios:
  • Patients with contraindications to iodinated contrast (42% of MRA orders in ED settings) 3
  • Patients with renal insufficiency (42% of MRA orders in ED settings) 3
  • Follow-up imaging to reduce cumulative radiation exposure 5
• Examination of hemodynamically unstable patients may be challenging with MRA due to longer acquisition times 2

Diagnostic Accuracy Comparison

• MRA has demonstrated 100% sensitivity (95% CI 70% to 100%) for aortic dissection diagnosis, compared to 93% for CT and 88% for TEE 1
• MRA can clearly demonstrate the extent of dissection and depict the distal ascending aorta and aortic arch in more detail than transesophageal echocardiography 2
• In direct comparison studies, MRA has shown superior performance to TEE in the evaluation and follow-up of thoracic aortic dissection 6

Practical Implementation

• When ordering MRA for aortic dissection, specify "MRA chest without and with IV contrast" to ensure optimal protocol selection 1
• For comprehensive evaluation, consider "MRA chest, abdomen, and pelvis without and with IV contrast" if there is concern for extension of dissection 1
• Be aware that median ED arrival to MRA completion time is approximately 311 minutes, which may impact management decisions in acute settings 3
• Ensure that both axial images and additional planes are evaluated to avoid misinterpretation of normal anatomy or artifacts 2

MRA represents an excellent diagnostic tool for aortic dissection, particularly when CT is contraindicated. However, the choice between imaging modalities should consider the patient's clinical stability, contrast contraindications, and the immediate availability of imaging resources.