Introduction - AAS
Acute aortic syndrome (AAS) is a
constellation of potentially life-threatening
acute aortic diseases.
Penetrating aortic ulcer,
Traumatic aortic rupture,
Unstable/ ruptured aneurysm.Dr.M.A.Suthaharan.
Diagram shows three layers of normal aortic wall, from
inner to outer: intima (I), media (M), and adventitia (A).Dr.M.A.Suthaharan.
Imaging Protocol - CT
A non-enhanced scan of the thoracic aorta is
included for the detection of an intramural
Iodine 350mg/ml; 120ml _ 4ml/sec followed by
50ml saline chase
18 g peripheral canula; R/ arm
Bolus triggering -ROI indescending aorta , 150
HU; be prepared for manual staring with visual
arterial phase 20 sec, venous phase 60 secDr.M.A.Suthaharan.
Contrast differences between arterial and venous
phase can be helpful in differentiating true and false
The iliac tract is included for evaluation of
endovascular treatment possibilities.
The branches of the arch are visualized to evaluate the
extend of dissection and awareness of possible
Visceral perfusion in both phases
Stanford Classification of AAS
• Stanford Type A lesions involve the ascending aorta and
aortic arch and may or may not involve the descending
• Stanford Type B lesions involve the thoracic aorta distal
to the left subclavian artery.
Most common non-traumatic acute aortic emergency
overall in-hospital mortality of 20–25%, which increases
markedly in patients with complicated dissection.
advancing age and hypertension.
Cystic medial degeneration in connective tissue disorders
(Marfan’s syndrome and Ehlers–Danlos syndrome
bicuspid aortic valve,
blunt chest trauma.
Events leading to aortic dissection from formation of entrance tear and exit tear of intima to
splitting of aortic media and formation of intimomedial flap. Blood under pressure dissects
media longitudinally, and double-channel aorta is formed with blood filling both true and
Aortic dissection is initiated by an intimal tear,
which allows blood to penetrate into the medial
Producing a cleavage plane (false lumen) between
the inner two-thirds and outer one-third of media.
The true lumen is separated from the false lumen
by an intimomedial flap.
The blood course through the medial layer can
variably extend the dissection distal or proximal to
the entry tear and
eventually rupture through the adventitia or
back through the intima into the true lumen, creating
Branching vessels can be involved
The false lumen may thrombose completely or
partially over time.
Reduction in the amount of elastic tissue within
the wall of the false lumen may lead to subsequent
Unenhanced CT may demonstrate internal displacement of
excellent sensitivity and specificity that
In BBFSE sequences it appears linear inside the
black vessel lumen
The false lumen can be differentiated from the
true lumen by its higher signal intensity due to the
fast spin-echo sequence in the sagittal plane -to
define the extension of the dissection in the
thoracic and abdominal aorta, including the aortic
arch branches .Dr.M.A.Suthaharan.
accurate definition of the anatomical details of the
dissection (extension, site of entry and re-entry
tear, aortic branch relationships) relies on
gadolinium-enhanced 3D MRA and its reformatted
SSFP technique- high-contrast resolution between
the aortic lumen and the wall that may be used for
morphological (2D or 3D images) or functional
(cine sequences) analysis
Axial BBFSE image of chronic type B aortic dissection.
The intimal flap is well depicted as a straight hyperintense
line dividing the true and false lumen at the level of
unusual type of aortic dissection is the intimo-intimal
intussusception produced by,circumferential dissection of
the intimal layer, which subsequently invaginates like a
Dissection into abdominal
Impaired perfusion of end-organs can be due to 2
1) static = continuing dissection in the feeding artery
(usually treated by stenting)
2) dynamic = dissection flap hanging in front of
ostium like a curtain (usually treated with
This may be hard to discern, MPR's can be helpfull.
Look for the re-entry point, usually to be found in
the iliac tract.
Provide information about tortuisity and
calcifications of the iliac tract if endovascular
procedures are being considered.
The following anatomical details need to be
considered for planning of endovascular treatment
of aortic dissection.
• The distance between the proximal neck, the
tear and the origin of the epiaortic vessels.
• The origin of the visceral vessels in regard to
the true or false lumen must be defined.
If one or more vessels arise from the false lumen, a
re-entry tear ensuring vessel perfusion after stent-
graft deployment has to be identified.
Careful evaluation of ascending aorta and aortic arch
dimensions and degree of atheromatous wall changes
Ascending aorta and archaneurysms may favour a
retrograde extension of the dissection if the proximal
end of the stent graft (free flow extremity) is
positioned in the distal arch.
Intramural hematoma is thought to begin with the
rupture of the vasa vasorum, within the medial
layer and eventually results in a circumferentially
oriented blood collection.
The hematoma may propagate along the media
layer of the aorta .
Itweakens the aorta and may progress either to
outward rupture of the aortic wall or to inward
disruption of the intima, the latter leading to
communicating aortic dissection
Note that the IMH
does not spiral
around the true
lumen, like in
classic AD, helping
visualised by cross-sectional imaging as an aortic
wall thickening, symmetric or asymmetric,
variable in thickness from 3 mm to more than 1 cm
it must be differentiated from mural thrombus or
Intimal displacement of calcification can aid in
because the IMH is a subintimal lesion, with
calcifications displaced on top of the lesion facing
Acute IMH is hyperdense on unenhanced CT.
shape of the aortic wall thickening: in IMH the
borders are generally smooth, while a thrombus or
a plaque are typically characterised by irregular
In the suspecion of IMH it is important to perform
in the acute phase the haematoma appears as a
crescent-like aortic wall thickening
typically hyperdense on unenhanced CT with respect
to the aortic lumen,
while after enhancement the density of wall and
lumen are reversed, with the IMH remaining
unenhanced, unlike the false lumen in aortic
The differentiation between IMH and a completely
thrombosed false lumen may be very difficult
IMH maintains a constant circumferential relationship
to the wall (subintimal lesion), while the thrombosed
false lumen tends to longitudinally spiral around the
IMH does not reduce the lumen, which maintains its
regular shape, while the false lumen can variably
compress the true lumen
The diagnosis of IMH is mainly based on axial
but 2D reformatted images may be useful to
evaluate the extent of IMH and its relationships
with aortic branches.
Type A or Type B
Regression to normal in 80% of patients
Predictors of mortality:
- Ascending Aorta > 5 cm
- IMH thickness > 2 cm
- Pericardial effusion (to less extend pleural
IMH may persist or evolve into aneurysm or PAU
Associated PAU - worse prognostic outcome
Pre-op evaluation of AAS
1. confirm or exclude the presence of impending
aortic rupture or
2. any other signs of severe instability that deserve
immediate surgical or endovascular treatment,
e.g. a visceral malperfusion in aortic dissection.
3. should define anatomical conditions allow an
endovascular or surgical treatment of the disease.
Aortic aneurysm is a localised or diffuse dilatation
involving all layers of the aortic wall, exceeding
the expected aortic diameter by a factor of 1.5 or
False aneurysm or pseudoaneurysm the wall is
represented only by the adventitial layer.
false aneurysms result from a contained
ruptureand should not be considered stable.
As many as 95% of atherosclerotic aneurysms
affect the abdominal rather than the thoracic aorta
Natural history of aneurysms is progressive
remodelling, expansion and eventual rupture.
defined as dilation of the aorta with a thickened
aneurysm wall, marked perianeurysmal and
retroperitoneal fibrosis, and dense adhesions to
adjacent abdominal organs.
Infection can cause thrombosis of the vasa
vasorum with consequent destruction of the aortic
intima and media.
Rupture of Aortic Aneurism
Aortic rupture appears on CTA images as a
Discontinuity of the aortic wall with contrast medium
it is typically associated with a large, periaortic
On unenhanced CT images the rupture can be
suspected if there is a discontinuity of wall
Tangential calcium sign
LEFT: Subtle periaortic stranding, MIDDLE: Hemorrhage
into posterior pararenal and perirenal compartment,
RIGHT: Extravasation of iv. Contrast.
The intimal calcification points away from the
aneurysm ( tangential calcium sign) and there is
A positive aortic drape sign is considered to be present when the
following features are seen:
• area in which the posterior aortic wall is unidentifiable as a distinct
• the posterior aorta follows the contour of the spine on one or both
2 weeks later
Size and extension of the aneurysm.
Adequate distance (>15 mm) between the
proximal neck of the aneurysm and the origin of
the epiaortic vessels
Distance of the peripheral neck of the aneurysm
and its relationship to the origin of the visceral
arteries (should be >15 mm)
Extent and type of wall alterations (e.g. amount of
atheromatous material or calcium) at the proximal
and distal neck
Diameter and condition of the abdominal aorta and
vascular access (iliac and femoral arteries) and
tortuosity of descending aorta which might
preventpassage of the stent-graft delivery system.
Any evidence for the presence of a large radicular
artery supplying the spinal cord that could be
covered by a stent graft
Any other incidental findings in the chest,
abdomen, or pelvis that should contraindicate the
procedure (e.g. metastatic tumour spread)
AAS are medical emergencies
Radiologist plays very important role in diagnosis,
planning of management, endovascular
interventions , post-op evaluation and follow up.
MDCT is investigation of choice; correct CT
technique and systematic reporting are very
important for management.