Can ultrasound (u/s) be used to diagnose an aortic dissection?

Ultrasound for Aortic Dissection Diagnosis

Ultrasound can be used to diagnose aortic dissection with high sensitivity, but it should not be the sole diagnostic modality due to limitations in visualization of certain aortic segments, particularly in the setting of acute aortic dissection where CT angiography remains the preferred first-line imaging test.

Diagnostic Capabilities of Ultrasound in Aortic Dissection

Transthoracic Echocardiography (TTE)

• TTE has limited sensitivity (77-80%) for detecting aortic dissection, particularly for dissections involving the descending aorta (only 70% detection rate) 1
• Major limitations include poor visualization in patients with abnormal chest wall configuration, obesity, pulmonary emphysema, and mechanical ventilation 1
• TTE alone is insufficient for comprehensive evaluation but can be valuable in hemodynamically unstable patients 1

Transesophageal Echocardiography (TEE)

• TEE has significantly higher sensitivity (99%) and specificity (89%) for aortic dissection when performed by experienced examiners 1
• When limited to surgical/autopsy confirmation, TEE sensitivity decreases to 89% with specificity of 88% 1
• TEE can be performed as the sole diagnostic procedure in hemodynamically unstable patients in the ICU or operating room 1
• Major limitation is the "blind spot" in visualizing small dissections in the distal ascending aorta and anterior portion of the aortic arch 1

Point-of-Care Ultrasound (POCUS) Protocols

• The SPEED protocol (combining TTE and abdominal aorta ultrasound) demonstrates 93.2% sensitivity and 90.9% specificity for aortic dissection 2
• Key sonographic findings include pericardial effusion, intimal flap, or aortic outflow track diameter >35 mm 2

Comparison with Other Imaging Modalities

CT Angiography

• CTA is the preferred first-line imaging test with sensitivity of 93-95% and specificity of 87-100% 1
• Emergency physicians may use CTA to exclude thoracic aortic dissection as it has accuracy similar to TEE and MRA 1
• CTA provides additional benefit of detecting alternative diagnoses in 13% of cases without aortic disorders 1

Magnetic Resonance Angiography (MRA)

• MRA demonstrates the highest sensitivity (100%) for aortic dissection diagnosis 1, 3
• MRA provides excellent visualization of dissection extent but is often not available in emergency settings 3

Clinical Applications and Recommendations

When to Use Ultrasound for Aortic Dissection

• In hemodynamically unstable patients where rapid bedside assessment is needed 1
• When profound hemodynamic instability exists, TEE can be performed as the sole diagnostic procedure before emergency surgery 1
• For initial screening in emergency settings when other imaging modalities are not immediately available 4, 2

Pitfalls and Limitations

• Artifacts due to reverberation within the ascending aorta lumen can lead to false diagnoses, particularly by inexperienced observers 1
• Ultrasound is operator-dependent, requiring experienced examiners for accurate interpretation 1
• The "blind spot" in TEE prevents visualization of small dissections in the distal ascending aorta and anterior aortic arch 1

Diagnostic Algorithm for Suspected Aortic Dissection

1. For hemodynamically stable patients:

   • CTA is the preferred first-line imaging test 1
   • MRA is an excellent alternative if available and patient is stable 3

2. For hemodynamically unstable patients:

   • Perform bedside TTE immediately, though image quality may be inadequate for definitive diagnosis 1
   • If cardiac tamponade is identified on TTE, proceed directly to surgery 1
   • Consider TEE as the sole diagnostic procedure if expertise is available 1

3. When other imaging modalities are unavailable:

   • Use POCUS protocols combining TTE and abdominal aorta assessment 2
   • Look specifically for intimal flap, pericardial effusion, or dilated aortic root 4, 2
   • Transfer to a center with surgical capabilities if aortic dissection is suspected 1