Episode 5: Acute Aortic Syndrome

Discover the 4 D’s of Radiology DETECT - DESCRIBE - DIFFERENTIAL - DECISION

DETECT

Definitions

1.       Acute Aortic Dissection: Tear in the intima, separating intima and media and allowing blood to flow through a false lumen

2.       Penetrating Atherosclerotic Ulcer: Outpouching beyond aortic wall (often seen together with IMH, to follow)

3.       Intramural Hematoma: Historically thought to reflect bleeding of the vasa vasorum into the adventitial layers, probably more like dissection without identifiable communication. 

4.       Limited Intimal Tear 

5.       Leaking +/- ruptured aortic aneurysm: Aneurysm is dilation

Rate: 3.5 – 6/100,000 people are affected

Mortality rate is high and in hospital mortality rate ranges from 10 to >30%

Anatomy

Histology

• Intima: Endothelial cells
• Media: Smooth muscle and connective tissue  
• Adventitia: connective tissue, fibroblasts, macrophages, nerves and vessels
• Vasa Vasorum: Vessels that supply the artery with nutrients

Anatomy

• Root
• Ascending Aorta
• Aortic Arch
• Thoracic Aorta
• Descending Aorta

The anatomy and configuration of the ascending aorta and arch allows for greater mobility compared to the descending segments. The most common site of trauma will be at the interface between the mobile segment and the fibrous remnant of the ductus arteriosus.

Clinical Presentation

Classic: Acute onset central chest pain radiating to the back

Other: Syncope (decreased cerebral perfusion or cardiac tamponade, diastolic murmur with aortic regurgitation, heart failure, pulse deficits or BP differences between 2 arms.

Complications:

1. Branch artery involvement:

•  Renal: oliguria, anuria
• Celiac, SMA, IMA: Abdominal pain

2. Compression of adjacent structures

• Ie. Esophagus, bronchi, left laryngeal nerve

Risk Factors:

• Long standing HTN: Smoking, dyslipidemia, cocaine
• Vascular: atherosclerosis, anatomical variants (aortic coarctation, bicuspid aortic valve), aneurysm
• Vascular Inflammation: Aortitis, Takayasu arteritis, giant cell arteritis, cystic medial necrosis
• CTD: Marfan’s,Ehler Danlos, Loeys-Dietz syndrome, relapsing polychondritis, ankylosing spondylitis
• Increased intraabdominal pressure: weight lifting, obesity
• Trauma
• Iatrogenic Factors: Catheters, previous vascular/aortic surgery

Classifications

Stanford and Debakey

• Stanford: A – involving the ascending aorta to the proximal origin of the brachiocephalic artery
• Stanford B – Any dissection distal to the branch vessels

SVS/STS Classification

• Based on the Stanford classification and then numbered from 0 to 11 which will tell you where the entry tear and exit tears are.

Timing:

1. Acute: 0 – 2 weeks
2. Subacute: 2 weeks – 3 months
3. Chronic: > 3 months

DESCRIBE

Imaging Workup

1. CXR
2. CT Chest without and with IV contrast from the base of the neck to just below the greater trochanters
3. Bedside and dedicated US Echocardiography

CXR Findings

Normal in 10 – 40% of cases

Common findings

Aortic Findings

• Widened mediastinum
• Loss of AP window
• Left apical pleural capping
• Rightward deviation of trachea and downward displacement of left main bronchus
• Double Calcium Sign: inward displacement of intimal calcifications
• Ill defined aortic enlargement

Complications:

• Pleural effusion
• Enlarged cardiac contours – pericardial effusion

CT Findings

Mnemonic – DISSECTION

• Efficient and organized reporting is crucial to optimize patient care

DISSECTION

1. D: Dissection or other acute aortic syndrome?

• Look at signs of acute rupture vs. chronic and corelate with clinical symptoms

2. I: Initiating primary intimal tear

• Most common locations: A – sinotubular origin, B – distal to the left subclavian artery
• Comment on the size, location (either inner or outer curvature)
• Intimal tears > 10 mm have worse prognosis
• Intimal tears on the inner curvature can move retrograde and become type A if not already

3. S: Size

• Size of the affected aorta where it is largest and the size of the false lumen
• Measure at the largest diameter of the aorta – orthogonal measurements are preferred, but greatest diameter in axial
• Acute: Beak and cobweb signs of the false lumen

4. S: Segment:

• Segments of the aorta are key to know
• If the root is involved there is a 1-2% increased risk of mortality with every hour until definitive repair

5. E: Extent

• How far does the acute aortic syndrome extend down into the branch vessels or iliofemoral?
• Think about the side branches, thromboses, involvement of the iliofemoral arteries. The SVS/STS classification system is helpful to systematically assessing the location

6. C: Complications

• Watch out for: Aortic rupture or contrast leak, hemopericardium, tamponade, coronary artery occlusion or dissection, cervical branch occlusion or stenosis, visceral organ infarcts, iliofemoral occlusion or thrombosis
• Mal-perfusion from Type A dissection increases mortality on the order of 45%
• Other AAS also have high mortality with risk of rupture quoted at 33 – 40%

7. T: Thrombus  

• Presence and location of thrombus in the false lumen as this can lead to upstream dilatation or mal-perfusion if the false lumen is supplying the branch vessels

8. I: Inspection of true and false lumen

• Assess the morphology and complexity
• Circumferential intimal tears are associated with increased complications and progression
• Non linear relationship with progressive thickening of the intimal flap

9. O: Other possibilities

• Put the findings together in association with the correct clinical context
• Think about what the underlying cause could potentially be

10. N: Notification

• Direct communication with the ordering provider

DIFFERENTIAL

Acute Aortic Dissection

Description

Spontaneous dissection of the aorta with presence of an intimal flap and false lumen

CT Findings

Acute:

• Thin and mobile dissection flap.

• May form the beak sign
• Cobweb sign (low attenuation wispy structures within the false lumen – strand of incompletely separated media)

Chronic: thick and immobile flap

Watch out for the mimic of ductus diverticulum which occurs just distally to the ligamentum arteriosum. It looks like a focal outpouching with smooth margins and no intimal tear.

Penetrating Atherosclerotic Ulcer

Description

Ulcer like plaque that erodes the intima causing remodeling and thickening of the outer layer.

Atherosclerosis is the major risk factor

CT Findings

Contrast filled outpouching (“mushroom shaped”)

Extensive atherosclerosis in other sites of the aorta

Usually a chronic process but may have acute on chronic presentation or leak.

Patients may have multiple PAU’s, so imaging of the entire aorta is key

Limited Intimal Tear

Description

Disease of the media with no significant separation of the vessel wall layers. A linear intimal tear occurs with local spread and exposure of the media and adventitia.

Relatively rare and can be difficult to visualize

CT Findings

Looks like a spontaneous pseudoaneurysm

Eccentric, one-sided bulge of the aortic wall

Intramural Hematoma

Description

Vasa vasorum that have ruptured/bled into the media of the aortic wall.

What: Spontaneous hematoma into aortic media due to rupture of vasa vasorum. May be associated with an aneurysm

Presentation: Intimal flap absent, absence of re-entrance tear from media into lumen leads to development of IMH

Population: Elderly

Epidemiology: Mortality similar to aortic dissection  

CT Findings

High attenuating material within the media.

Thickened eccentric crescent of high attenuation on non CE CT Study (usually > 50 HU)

Complications: Dissection, rupture, hemorrhage (pericardial, pleural, mediastinal)

Can be challenging to differentiate from thrombosed false lumen of a primary aortic dissection

If the thrombus extends greater than 1 aortic segment it may be that this is actually a thrombosed false lumen

Traumatic Acute Aortic

Description

Aortic wall injury caused by large external forces such as an MVA or fall from height

CT Findings

Dissection flap, pseudoaneurysm, IMH

Syndromes – Blunt

Description

The aorta is fixed at three main locations: The root, the isthmus and the hiatus – common sites for deceleration injuries

CT Findings

Local or distant mediastinal hemorrhage, mediastinal hematoma, Hemothorax, Peri-aortic hematoma.

Often mediastinal hemorrhages in the context of trauma are venous in origin, but if the fat plane along the aortic wall is lost, then one should consider an arterial bleed.

Leaking Aortic Aneurysm

Description

Thoracic Aortic Aneurysm (TAA)

Focal abnormal dilation of the aorta

Cause: HTN, atherosclerosis

Tears that extend past an aneurysm

Aneurysm (focal abnormal dilation of a blood vessel)

CT Findings

Findings of TAA

• Aortic enlargement
• Ascending aorta > 4 cm
• Descending thoracic aorta > 3 cm
• Measurements: True short axis images with double oblique short axis multiplanar reformatted images should be used.

• Leak and concern for rupture: Drooped aorta along the thoracic vertebrae, high attenuating crescent, tangential calcium, focal discontinuity of calcifications
• Complications: Rupture, dissection, infection, endoleak, paraplegia (occlusion of the artery of ademkiewicz)

Poor Prognostic CT Features

Uncomplications

• No rupture
• No malperfusion
• No high risk features

High Risk Features

• Refractory pain
• Refractory hypertension
• Bloody pleural effusion
• Aortic diameter > 40 mm
• Radiographic only malperfusion
• Readmission
• Entry tear in the lesser curve location
• False lumen diameter > 22 mm
• Intimal tear > 10 mm

Complicated

• Rupture
• Malperfusion

Complications

Acute

1. Rupture
2. Cardiac tamponade
3. Valvular involvement
4. Coronary artery malperfusion and myocardial ischemia/infarction
5. Adventitial hematoma along the pulmonary artery with peribronchovascular hemorrhage
6. Mediastinal hematoma
7. Cerebral embolic stroke
8. Upper extremity ischemia
9. Static or dynamic side branch occlusion of the abdominal aorta
10. End organ ischemia: Bowel, Kidneys (L more common than R)
11. Lower extremity ischemia with iliofemoral occlusion
12. Effusions – often resolve with healing

Chronic

1. Persistent perfusion of the false lumen leading to dilation: Aneurysm and thrombus accumulation within the false lumen
2. Post – intervention complications: Endoleak, calcifications, thrombus, type of stent and/or repair, pseudoaneurysm

DECISION

Treatment

1. Stabilization
2. Medical: Pain, Blood Pressure, and Heart Rate control
3. Endovascular
4. Surgical:

•  Indications are type A dissection (involving the proximal ascending aorta). A number of different techniques are available depending on the size and exact location within the ascending thoracic aorta.

Follow up

• Repeat imaging at the time of discharge, 90 days, 6 months and at 1 year to ensure stability
• Depending on clinical status can also image 1/year or alternate with MRI depending on age of patient and concern for radiation exposure

Example Case Of Aortic Dissection

References

1. Murillo, H., Molvin, L., Chin, A. S., & Fleischmann, D. (2021). Aortic dissection and other acute aortic syndromes: diagnostic imaging findings from acute to chronic longitudinal progression.  RadioGraphics ,  41 (2), 425-446.
2. Ohle, R., Yan, J. W., Yadav, K., Cournoyer, A., Savage, D. W., Jetty, P., ... & Lang, E. (2020). Diagnosing acute aortic syndrome: a Canadian clinical practice guideline.  CMAJ ,  192 (29), E832-E843.
3. Ueda, T., Chin, A., Petrovitch, I., & Fleischmann, D. (2012). A pictorial review of acute aortic syndrome: discriminating and overlapping features as revealed by ECG-gated multidetector-row CT angiography.  Insights into Imaging ,  3 (6), 561-571.
4. Lombardi, J. V., Hughes, G. C., Appoo, J. J., Bavaria, J. E., Beck, A. W., Cambria, R. P., ... & Wang, G. J. (2020). Society for Vascular Surgery (SVS) and Society of Thoracic Surgeons (STS) reporting standards for type B aortic dissections.  The Annals of thoracic surgery ,  109 (3), 959-981.
5. McMahon, M. A., & Squirrell, C. A. (2010). Multidetector CT of aortic dissection: a pictorial review.  Radiographics ,  30 (2), 445-460.
6. Yang, B., Patel, H. J., Williams, D. M., Dasika, N. L., & Deeb, G. M. (2016). Management of type A dissection with malperfusion.  Annals of cardiothoracic surgery ,  5 (4), 265.
7. Kapoor, H., Lee, J. T., Orr, N. T., Nisiewicz, M. J., Pawley, B. K., & Zagurovskaya, M. (2020). Minimal aortic injury: mechanisms, imaging manifestations, natural history, and management.  RadioGraphics ,  40 (7), 1834-1847.