What is the best test for aortic dissection if unable to use Intravenous (IV) contrast?

Best Test for Aortic Dissection Without IV Contrast

MRA chest without IV contrast using ECG-gated balanced steady-state free precession (bSSFP) sequences is the best imaging test for diagnosing aortic dissection when IV contrast cannot be used. 1

Primary Recommendation

Non-contrast MRA with bSSFP sequences achieves near 100% accuracy for detecting thoracic aortic dissection, intramural hematoma, and penetrating aortic ulcer when compared against contrast-enhanced imaging. 1 This technique provides inherent contrast between blood pool and vessel wall without requiring gadolinium administration. 1

Key Technical Requirements

• ECG-gating is essential to minimize cardiac motion artifacts and ensure accurate measurements, particularly in the ascending aorta where cardiac pulsatility can degrade image quality 1
• Respiratory gating improves accuracy by compensating for motion, though this increases acquisition time to tens of minutes 1
• Acquisition should include transversal, coronal, and parasagittal planes along the aortic arch curvature 1

Diagnostic Performance

The evidence strongly supports non-contrast MRA:

• Sensitivity approaches 100% for detecting aortic dissection 2, 3, 4
• Specificity of 97.8-100% for dissection diagnosis 3, 4
• Superior to transesophageal echocardiography which has lower specificity (68-79%) due to false positives in the ascending aorta 3, 4
• Accurately identifies entry/reentry tears, thrombus formation, pericardial effusion, and aortic regurgitation 2, 3

Alternative When MRA Unavailable

If MRA is not immediately available (common in emergency settings 2, 5):

Non-contrast CT chest can detect aortic dissection through indirect findings, though with significantly lower sensitivity than contrast-enhanced imaging 6:

• Displaced calcified intimal flap (most specific finding) 6
• Intraluminal high-density linear structures 6
• Intramural hematoma (appears as hyperattenuating crescent >45 HU in aortic wall) 1
• Aneurysmal aortic dilation 6

However, non-contrast CT has poor sensitivity and should only be used when both IV contrast and MRA are contraindicated. 6

Clinical Algorithm

1. First-line: MRA chest without IV contrast with ECG-gated bSSFP sequences 1

   • Extend to chest/abdomen/pelvis if dissection may involve abdominal aorta 1
   • Acquisition time: 20-30 minutes with gating 1

2. If MRA unavailable or patient too unstable to tolerate long scan time:

   • Consider transesophageal echocardiography (bedside capability, 98% sensitivity) 3, 4
   • Accept lower specificity (77-79%) with false positives in ascending aorta 3, 4

3. If both MRA and TEE unavailable/contraindicated:

   • Non-contrast CT chest as last resort 6
   • Look specifically for displaced calcified intimal flap and intramural hematoma 6
   • Recognize this has low sensitivity and may miss dissection 6

Important Caveats

• MRA often not available emergently, limiting use in acute unstable presentations 2, 5
• Longer acquisition times (tens of minutes) may be problematic in unstable patients 1
• Artifacts from surgical material can occur with bSSFP sequences, though less problematic than with contrast-enhanced sequences 1
• Both thoracic and abdominal aorta should be imaged since intramural hematoma in thoracic aorta may be associated with true dissection in abdominal aorta 2
• A "blind spot" exists in the distal ascending aorta and anterior aortic arch due to tracheal/bronchial interposition 2