Best Diagnostic Test for Aortic Dissection
CT angiography (CTA) of the chest, abdomen, and pelvis is the diagnostic test of choice for suspected aortic dissection in stable patients. 1, 2
Primary Diagnostic Approach
CTA is recommended as first-line imaging because it combines exceptional accuracy (sensitivity 93-100%, specificity 98-100%), wide availability at all hours in emergency departments, rapid acquisition time, and comprehensive anatomic detail in a single study. 1, 2 The 2022 ACC/AHA guidelines explicitly state that CT is recommended for initial diagnostic imaging given these advantages. 1
Key Advantages of CTA:
- Identifies the full extent of dissection, entry tear location, branch vessel involvement, signs of malperfusion, pericardial effusion, and periaortic hematoma in one examination 1, 2
- Detects alternative diagnoses in 13% of cases without aortic pathology, which TEE cannot accomplish 1
- Does not require patient transport to specialized areas once in the radiology suite 1
- Provides treatment planning information for surgical teams immediately 1, 2
Alternative Imaging for Specific Clinical Scenarios
Hemodynamically Unstable Patients:
Transesophageal echocardiography (TEE) should be performed at the bedside or in the operating room as the sole diagnostic procedure before emergency surgery in unstable patients who cannot be safely transported. 2, 3 TEE has sensitivity of 88-98% and specificity of 95-100%. 1, 2, 3
When CT is Contraindicated:
TEE or cardiac MRI are reasonable alternatives when iodinated contrast allergy exists or renal function prohibits contrast administration. 1 MRI demonstrates the highest sensitivity (100%) but is rarely used acutely due to longer acquisition times, limited availability, and difficulty monitoring unstable patients in the scanner. 1, 2
Critical Pitfalls to Avoid
Do not use transthoracic echocardiography (TTE) alone to exclude aortic dissection. TTE has inadequate sensitivity (59-80%) and cannot visualize the distal ascending aorta, aortic arch, or descending thoracic aorta adequately. 3, 4 A negative TTE requires confirmatory imaging with CTA, TEE, or MRI. 3
Do not order multiple sequential imaging tests, as this causes unnecessary time delays and increases mortality risk in a condition with 1-2% mortality per hour. 2, 5 Choose the single most appropriate test based on patient stability and institutional availability. 2
Do not rely on chest X-ray for diagnosis. While abnormal in 60-90% of cases, plain radiography is neither sufficiently sensitive nor specific to confirm or exclude dissection. 1
Adjunctive Testing
D-dimer below 500 ng/mL combined with low clinical risk scores (aortic dissection detection risk score or AORTAs score) may help exclude dissection in low-probability patients, but elevated D-dimer is nonspecific and cannot differentiate dissection from pulmonary embolism or acute myocardial infarction. 1 D-dimer should not be used as a standalone test and false negatives occur in patients with thrombosed false lumens or intramural hematomas. 1
Imaging Protocol Requirements
Every imaging study must address: confirmation of diagnosis, classification (Stanford Type A vs B), differentiation of true from false lumen, localization of intimal tears, assessment of branch vessel involvement, detection of aortic regurgitation, and identification of extravasation or pericardial effusion. 2 For CTA, the protocol should include non-contrast imaging followed by contrast-enhanced acquisition from thoracic inlet to pelvis. 2