Imaging Algorithms in Acute Aortic Syndromes

1. Sanjiv Sharma
All India Institute of Medical Sciences
New Delhi
Imaging Algorithms in Acute
Aortic Syndromes

2. Acute
Aortic
Syndrome
IMH PAU
Aortic Dissection
”characterised by aortic pain
with a history of HT”
Villacosta I, San Román JA. Acute aortic
syndrome. Heart 2001;85:365-8
common denominator is disruption of aortic
media with bleeding within the layers
Acute Aortic Syndrome

3. Acute Aortic Syndrome
• A tear or an ulcer allows blood
to penetrate from aortic lumen
into media or rupture of ‘vasa
vasorum’
• Inflammatory response to blood
in media further initiates
necrosis & apoptosis leading to
degeneration of elastic tissue,
that can cause further aortic
dilatation or rupture

4. Lack of diagnosis at initial evaluation: 42% of patients
(Spittell PC, Mayo Clin Proc 1993; 68:642)
Early Accurate Diagnosis Is a Key to Survival
AAS: A Medley of Great Mimickers

5. Predisposing Factors
• Hypertension
• Connective tissue disorder
• Bicuspid aortic valve
• Coarctation
• Previous cardiac surgery
• Recent percutaneous
instrumentation
• Deceleration injuries
• Cocaine abuse
• Peri-partum period

6. Diagnosis of Acute Aortic
Syndrome
• Rapid imaging essential to avoid
delay in detecting potentially life-
threatening complications
• Frequent combination of:
* missed diagnosis
* atypical presentation
* time-dependent morbidity &
mortality
• Selection of optimal imaging
technique is critical for diagnosis
& treatment planning

7. Goals of Imaging
• Establish diagnosis & localize type
• Anatomical features
* presence of absence of dissection
* location, extent
* Sites of entry & reentry
* False lumen patency
(partial or complete thrombosis)
* Relation to branch vessels
• Complications of dissection
a Type A
i Aortic regurgitation
ii Coronary artery involvement
iii Pericardial, mediastinal or pleural effusion
b Aortic rupture- contained or frank
c Branch vessel involvement
d Malperfusion

8. Imaging Techniques
• Chest Radiograph
• ECHO
• CT Angiography
• MRI
• Catheter
angiography

9. Factors Determining Choice of
Imaging Technique
• Hemodynamic stability
• Renal function/GFR
• Complication-
presence/absence
(based on clinical
assessment)
• Availability of imaging
techniques
• Local expertise

10. Chest Radiograph
• Widening mediastinum (80% to
90% of cases (83%, type A; 72%,
type B)
• Obliteration of aortic knob
• Displaced intimal calcification
(>5 mm) -calcium sign
• Displacement of trachea to
right
• Distortion of left main-stem
bronchus
• Pleural effusion (more common
left sided)
• Cardiomegaly
• Normal in 12% to 15% of cases
Challenge- findings often nonspecific;
In appropriate clinical setting, chest
radiograph can be very helpful

11. Echocardiography for Acute
Aortic Syndrome
• TTE provides vital prognostic
information
* new-onset aortic insufficiency
* pericardial effusion
* visualization of proximal dissection
* LV function & wall motion
• Portable, avoids transport of a critically
ill patient; use in operating theatre
• TEE improves diagnostic accuracy
• European Cooperative Study Group, IRAD
- 99% sensitivity, 89% specificity, 89%
PPV & 99% NPV
• Adjunctive use of colour Doppler-
* confirm blood flow in true & false lumen
* identify communication sites
* see dynamic side-branch obstruction
• Limited by:
* operator dependence
* insufficient anatomic detail for EVR

12. MDCT for Diagnosis & Treatment
Planning
• Standard of Care today for
optimal evaluation
• Sensitivity- 85-98%, Specificity-
100%, NPV-85-96%, PPV-100%
• ECG gating can eliminate
pulsation artifacts
• Establish diagnosis, identify type
as well as complications
• Very useful for treatment
planning (surgical or endovascular)
• Risk of radiation & iodinated
contrast

13. MRI for diagnosis of Acute
Aortic Syndrome
• Complementary rather than
competing imaging modality for
thoracic aorta
• Advantages
- No radiation
- No use of iodinated contrast
• Disadvantages
- Limited availability
- Long acquisition time
- Gadolinium contrast caution in renal
impairment

14. MRI for Acute Aortic Syndrome
• Sensitivity- 98%,
specificity- 98%
• Capable of multi-planar
imaging with 3-D
reconstruction
• Cine MRI visualize blood
flow, differentiating slow
flow and clot and AR
• MRA can identify all
complications- AR,
pericardial effusion & branch
vessel morphology
Little applicability in acute settings!
Challenges of speed & clinical condition

15. Catheter Angiography for Diagnosis
• Diagnostic accuracy 90-
95%
• Identify intimal flap, true and
false lumen
• Thickened wall (thrombosed
false lumen)
• AR, branch vessel
involvement
• 5-10% false negative rate
 thrombosed false lumen
 simultaneous opacification
of both lumens
 misses IMH
• Risks of procedure
Has no place in the diagnostic algorithm if
orthogonal imaging techniques are available

16. Neurologic Manifestations
• May dominate clinical
presentation
• Neurologic syndromes
include:
• Persistent or transient
ischemic stroke
• Spinal cord ischemia
• Ischemic neuropathy
• Hypoxic encephalopathy

17. Syncope
• Reported in up to15% of patients in
IRAD
• Indicate development of dangerous
complications
• Acute hypotension - Cardiac
tamponade (10% of acute type A
dissections) or aortic rupture
• Cerebral vessel obstruction or
activation of cerebral baro receptors

18. Vascular insufficiency
• Renal artery - 5% to 10%
• Renal ischemia, infarction,
renal insufficiency or
refractory hypertension
• Mesenteric ischemia or
infarction in 5%
• Extension to iliac arteries
-acute limb ischemia

19. Acute Myocardial Infarction
• Flap causing mal-perfusion
of coronary artery
• Occurs in 1-7% of acute
type A dissections
• RCA is most commonly
involved

20. Pleural & pericardial effusion
• Left-sided pleural
effusion
• Usually related to
inflammatory
response
• Acute hemothorax

21. Intramural Hematoma
• Hemorrhage of vasa vasorum in
medial layer of aorta or hematoma
arises from microscopic tears in aortic
intima
• Most (50-85%) are located in
descending aorta
• Association with hypertension
• 10-20% can have an acute aortic
syndrome
• Common in older patients
• Clinical picture of dissection
Markers of Prognosis- Location, thickness & presence of PAU

22. Evolution of IMH
• Complete resolution (10-30%)
• Convert to classic dissection (3-14% of
descending aorta & in 11-88% of ascending
aorta)
• Aorta may enlarge & develop into an
aneurysm

25. Penetrating Aortic Ulcer
• Atherosclerotic lesion penetrates
internal elastic lamina into media
• Associated with variable degree of
IMH
• May lead to pseudo aneurysm,
rupture, or late aneurysm
• 2-8% of acute aortic syndrome
• Acute chest or back pain, similar to
dissection
• More common in descending aorta
(61.2%), Abdominal aorta (29.7%) ,
Arch of aorta (6.8%)
• 25% of PAUs are found incidentally

26. When should you intervene in
Penetrating Aortic Ulcer?
• Ascending aorta location
• Interval development of
hemorrhage
• Peri-aortic hematoma
• Expanding pseudo
aneurysm or rupture
• Increasing aortic wall
thickness
• Ulcer crater >20 mm in
diameter or >10 mm in
depth
• Increasing pleural effusion

27. Imaging algorithm
Acute aortic syndrome
(Clinical & Chest Radiograph)
Window inadequate
or signs of asc ao involvement
TTE
MDCT angiography
(non-contrast f/b
contrast scan)
OR
MRI with CE-MRA
Stable patient
Patient in shock
MDCT angiography
(non-contrast f/b
contrast scan)
TEE
TEE Unavailable or
Imaging inadequate
Normal
?Type B
MDCT angiography
(non-contrast f/b
contrast scan)
Unstable patient
(no shock)