AJR 2003; 181:309-316
© American Roentgen Ray Society
Pathogenesis in Acute Aortic Syndromes: Aortic Dissection, Intramural Hematoma, and Penetrating Atherosclerotic Aortic Ulcer
Katarzyna J. Macura1,
Frank M. Corl,
Elliot K. Fishman and
David A. Bluemke
1 All authors: The Russell H. Morgan Department of Radiology and Radiological
Science, Johns Hopkins Medical Institutions, 600 N. Wolfe St., Baltimore, MD
21287-0750.
Received July 26, 2002;
accepted after revision December 17, 2002.
Address correspondence to K. J. Macura.
Introduction
Acute aortic syndromes refer to the spectrum of aortic emergencies that
include aortic dissection, intramural hematoma, penetrating atherosclerotic
ulcer of the aorta, aortic aneurysm leak and rupture, and traumatic aortic
transection. The aortic wall is composed of three layers
(Fig. 1): the inner layer of
intima, the middle layer of media, and the outer layer of adventitia. Multiple
mechanisms are involved in the disruption of the aortic wall layers, leading
to various acute aortic syndromes. This pictorial essay focuses on the
distinction of a typical aortic dissection from an intramural hematoma and
penetrating atherosclerotic ulcer.
Aortic Dissection
A classic aortic dissection begins with a laceration of the aortic intima
and inner layer of the aortic media, forming an entrance tear that allows
entering blood to split the aortic media
[1]. The splitting of the media
is responsible for formation of a double-channel aorta, with an aortic
dissection flap dividing the aortic lumen into true and false lumens (Figs.
2 and
3A,
3B). The intima and the inner
part of the aortic media form the intimomedial flap. The flap tissue is
composed mainly of aortic media delaminated from the aortic wall
[2]. The outer portion of the
aortic media and adventitia form the outer wall of the false channel.
Reentrance tears are usually present in the intima, creating additional
communication between the true and false lumens in the distal aorta. The true
lumen is usually small with high-velocity flow, whereas the false lumen is
larger with slower velocity, turbulent blood flow (Fig.
4A,
4B).

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Fig. 2. Diagram illustrates 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 false lumens.
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Fig. 3A. 46-year-old man with concurrent intramural hematoma involving
ascending aorta and communicating dissection involving descending aorta. Axial
unenhanced CT scan shows hyperdense crescentic hematoma in wall of ascending
aorta (white arrow) with eccentric narrowing of lumen, type A
intramural hematoma. Small intramural hematoma (arrowhead) is also
noted at left lateral aspect of proximal descending aorta. High-attenuation
dissection flap (black arrow) is seen in descending aorta.
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Fig. 3B. 46-year-old man with concurrent intramural hematoma involving
ascending aorta and communicating dissection involving descending aorta. Axial
contrast-enhanced CT scan obtained at same level as A shows wall
thickening in ascending and descending aorta, but high-attenuation intramural
hematoma is less obvious. Classic intimomedial flap (arrow) dividing
true and false lumens in descending aorta is more conspicuous after contrast
administration. Note irregular margin of flap on false lumen side. Intramural
hematoma (arrowhead) is seen along lateral wall of false lumen.
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Fig. 4A. Axial double-inversion-recovery MR images (TR/TE, 1875/18; inversion
time, 150 msec) of 37-year-old man with Marfan syndrome. Image shows classic
aortic dissection with double-channel aorta. True lumen (straight
arrow) is smaller than false lumen (curved arrow). High-velocity
flow in true lumen causes signal void. Slower flow with higher signal can be
seen in false lumen.
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Fig. 4B. Axial double-inversion-recovery MR images (TR/TE, 1875/18; inversion
time, 150 msec) of 37-year-old man with Marfan syndrome. Image shows swirling
flow pattern in false lumen (curved arrow). True lumen (straight
arrow) is significantly narrowed but patent.
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Cystic medial necrosis associated with connective tissue disorders was once
believed to contribute to degeneration of the aortic media leading to aortic
dissection. However, a study showed that a minority of patients with aortic
dissection exhibited medial degeneration
[3]. In most patients, the
primary event that allowed the blood to spread through the aortic media was
the intimal tear. When present, degenerative changes within the media and the
loss of the elastic tissue reduce the resistance of the aortic wall to
hemodynamic stress, leading to subsequent dissection. Hypertension-related
spontaneous rupture of the aortic vasa vasorum might lead to intramural
hematoma and subsequently to intimal tear. Intramural hematoma precedes
intimal rupture because hemorrhage of the vasa vasorum weakens the media, and
the arterial pressure from blood flow in the aortic lumen subsequently favors
the entrance of blood from the lumen into the aortic media
[1]. Atherosclerosis was once
thought to cause aortic dissection. However, there is an association between
an atheroma and the location of dissection in only a small number of patients
[1]. Dissection in the region
of gross atherosclerosis is usually limited by neighboring fibrosis and
calcification.
Mechanical forces contributing to aortic dissection include flexion forces
of the vessel at fixed sites, the radial impact of the pressure pulse, and the
shear stress of the blood. During the cardiac cycle, the heart and aorta
produce rhythmic movements, allowing all but fixed segments to move. These
fixed points of the aorta are exposed to the most significant flexion forces.
Classic type A and B aortic dissections produce an intimal tear at the areas
of greatest hydraulic stress: the right lateral wall of the ascending aorta or
the descending aorta in proximity to the ligamentum arteriosum (Fig.
5A,
5B,
5C). Hypertension adds to a
mechanical strain on the aortic wall and the shearing forces exerting a
longitudinal stress along the aortic wall (Figs.
6A,
6B,
6C,
6D and
7A,
7B,
7C). Decreased vasa vasorum
flow, occurring in arterial hypertension, may increase the stiffness of the
outer ischemic media of the aorta to produce interlaminar shear stresses
contributing to the development of aortic dissection.

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Fig. 5A. 68-year-old man with aberrant right subclavian artery and horseshoe
kidney. Axial contrast-enhanced CT scan obtained at level of origin of
aberrant right subclavian artery shows aberrant vessel (arrow)
crossing midline behind trachea and esophagus.
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Fig. 5B. 68-year-old man with aberrant right subclavian artery and horseshoe
kidney. Axial contrast-enhanced CT scan shows dissection involving aortic arch
with calcifications within intimomedial flap and different attenuation of
enhanced blood within true and false (arrow) lumens. Intimal tears
leading to dissection frequently form in areas of elevated hydraulic stress,
such as region of aberrant vessel origin.
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Fig. 5C. 68-year-old man with aberrant right subclavian artery and horseshoe
kidney. Anteroposterior volume-rendered CT image of origin of aberrant
subclavian artery depicts aberrant vessel course (arrow) better than
axial scans A and B.
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Fig. 6A. 61-year-old man with symptoms of right hemispheric stroke who was
found to have marked blood pressure discrepancy between arms and hypertension.
Urgent CT scan (not shown) revealed type A aortic dissection. Patient went
into asystole and died 15 hr after imaging. Axial contrast-enhanced CT scan
obtained at level of aortic arch shows complex dissection with intimomedial
flap involving arch and brachiocephalic artery (arrow). Dissection
extended into left common carotid artery (arrowhead) and into left
subclavian artery (not shown).
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Fig. 6B. 61-year-old man with symptoms of right hemispheric stroke who was
found to have marked blood pressure discrepancy between arms and hypertension.
Urgent CT scan (not shown) revealed type A aortic dissection. Patient went
into asystole and died 15 hr after imaging. Axial CT scan shows irregular
dissection flap within lumen of ascending and descending aorta
(arrows).
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Fig. 6C. 61-year-old man with symptoms of right hemispheric stroke who was
found to have marked blood pressure discrepancy between arms and hypertension.
Urgent CT scan (not shown) revealed type A aortic dissection. Patient went
into asystole and died 15 hr after imaging. Axial CT scan shows
hemopericardium (arrow) that was confirmed at echocardiography (not
shown) as large circumferential hyperechoic pericardial effusion with evidence
of right ventricle compression.
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Fig. 6D. 61-year-old man with symptoms of right hemispheric stroke who was
found to have marked blood pressure discrepancy between arms and hypertension.
Urgent CT scan (not shown) revealed type A aortic dissection. Patient went
into asystole and died 15 hr after imaging. Axial CT scan shows dissection
continuing along right wall of abdominal aorta (arrow). No
enhancement of right kidney parenchyma was present.
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Fig. 7A. 82-year-old man with thoracic aortic aneurysm type B and
thoracoabdominal aortic dissection extending from just distal to left
subclavian artery to proximal right common iliac artery. Patient was first
diagnosed with aortic dissection 12 years ago. For more than 10 years,
symmetric perfusion of kidneys was seen, until recently when CT showed
hypoperfusion of right kidney. Contrast-enhanced CT scan shows both true and
false (arrow) lumens to be well opacified with contrast material.
There is minimal delay in enhancement and thinning of cortex of right
kidney.
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Fig. 7B. 82-year-old man with thoracic aortic aneurysm type B and
thoracoabdominal aortic dissection extending from just distal to left
subclavian artery to proximal right common iliac artery. Patient was first
diagnosed with aortic dissection 12 years ago. For more than 10 years,
symmetric perfusion of kidneys was seen, until recently when CT showed
hypoperfusion of right kidney. CT scan obtained 1 year after A shows
decrease in attenuation of contrast-enhanced blood in false lumen
(arrow) when compared with true lumen. Enhancement of right kidney is
markedly diminished, which is compatible with progressive hypoperfusion.
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Fig. 7C. 82-year-old man with thoracic aortic aneurysm type B and
thoracoabdominal aortic dissection extending from just distal to left
subclavian artery to proximal right common iliac artery. Patient was first
diagnosed with aortic dissection 12 years ago. For more than 10 years,
symmetric perfusion of kidneys was seen, until recently when CT showed
hypoperfusion of right kidney. Anteroposterior volume-rendered CT image shows
right renal artery (open white arrow) originating from false lumen
(solid white arrow). Left renal artery (open black arrow)
originates from true lumen. Note dissection flap with calcifications
(solid black arrow) that separates true and false lumens.
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Aortic Intramural Hematoma
Aortic intramural hematoma may occur as a primary event in hypertensive
patients in whom there is spontaneous bleeding from vasa vasorum into the
media or may be caused by a penetrating atherosclerotic ulcer. Intramural
hematoma may also develop as a result of blunt chest trauma with aortic wall
injury. Intramural hematoma is thought to begin with the rupture of the vasa
vasorum, the blood vessels that penetrate the outer half of the aortic media
from the adventitia and arborize within the media to supply the aortic wall
(Fig. 8). The hematoma
propagates along the media layer of the aorta
[2]. Consequently, intramural
hematoma weakens 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
[4] (Fig.
9A,
9B).

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Fig. 9A. Axial double-inversion-recovery MR images (TR/TE, 1690/29; inversion
time, 150 msec) of 76-year-old man with progression of intramural hematoma to
overt dissection in ascending aorta within 6 days. Image shows
high-signal-intensity crescentic intramural collection in ascending aorta
(arrow), consistent with early subacute type A intramural
hematoma.
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Fig. 9B. Axial double-inversion-recovery MR images (TR/TE, 1690/29; inversion
time, 150 msec) of 76-year-old man with progression of intramural hematoma to
overt dissection in ascending aorta within 6 days. Image obtained 6 days after
A shows that intramural hematoma progressed to type A aortic dissection
within 6 days. Note signal intensity difference between true and false lumens.
Signal void within true lumen reflects high-velocity blood flow, whereas
higher signal within false lumen is related to slower, turbulent flow. Also
note defect in intimomedial flap (arrow) representing intimal
tear.
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Intramural hematoma can be distinguished from mural thrombus by
identification of the intima: mural thrombus lies on top of the intima, which
is frequently calcified, whereas intramural hematoma is subintimal. On
unenhanced CT, intramural hematoma is hyperdense (Fig.
3A,
3B). MR imaging can aid in the
distinction of slow flow in the false lumen of a dissection from no flow in an
intramural hematoma. Gradient-refocused echo pulse sequences, with the use of
cine image acquisition, show cyclical flow-related enhancement in the false
lumen of aortic dissection, whereas images of intramural hematoma show no
signal intensity change. Dynamic phase-contrast MR imaging is more sensitive
than gradient-refocused echo sequences for excluding slow flow in the
thickened aortic wall that would indicate aortic dissection rather than
intramural hematoma [5].
Penetrating Atherosclerotic Aortic Ulcer
In a penetrating aortic ulcer, an atheromatous plaque ulcerates and
disrupts the internal elastic lamina, burrowing deeply through the intima into
the aortic media [2,
6]. When an atherosclerotic
plaque penetrates into the media, the media is exposed to pulsatile arterial
flow, which causes hemorrhage into the wall that then leads to intramural
hematoma [7] (Figs.
10,
11A,
11B,
11C,
11D,
12A,
12B,
12C,
12D,
12E,
12F). The plaque may
precipitate a localized intramedial dissection associated with a variable
amount of hematoma within the aortic wall, may break through into the
adventitia to form a pseudoaneurysm, or may rupture. Ulceration of an aortic
atheroma occurs in patients with advanced atherosclerosis. On imaging, a
penetrating aortic ulcer can be distinguished from an atheromatous plaque by
presence of a focal, contrast-filled outpouching surrounded by an intramural
hematoma (Fig. 12A,
12B,
12C,
12D,
12E,
12F), which confirms the
aggressive behavior of the lesion. The atheromatous plaque with ulceration but
without penetration through the intima shows irregular margins, but no
contrast material extends beyond the level of intima, which is frequently
calcified, and no intramural hematoma is present (Fig.
13A,
13B).

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Fig. 10. Diagram shows events leading to penetrating aortic ulcer from
formation of extensive aortic atheroma confined to intimal layer, through
lesion progression to deep ulceration of plaque with penetration into media,
to entrance of blood from aortic lumen into media and splitting of media with
intramural hematoma. Hematoma formation may extend along media, resulting in
long-segment intramural hematoma.
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Fig. 11A. 58-year-old woman presenting with severe back pain and penetrating
atherosclerotic ulcer of aorta. Unenhanced CT scan shows crescentic
high-attenuation intramural hematoma (arrow) at distal thoracic
aorta.
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Fig. 11B. 58-year-old woman presenting with severe back pain and penetrating
atherosclerotic ulcer of aorta. Contrast-enhanced CT scan obtained at level
corresponding to A shows ulcer (arrow) filling with contrast
material. Note that intramural hematoma presents as eccentric low-attenuation
thickening of aortic wall.
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Fig. 11C. 58-year-old woman presenting with severe back pain and penetrating
atherosclerotic ulcer of aorta. Lateral angiogram of distal thoracic aorta
shows anterior ulcerlike aortic lesion (arrow) filling with contrast
material above level of celiac axis.
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Fig. 11D. 58-year-old woman presenting with severe back pain and penetrating
atherosclerotic ulcer of aorta. Multiplanar reformatted CT scan in sagittal
view shows ulcer crater (open arrow) and long-segment intramural
hematoma (solid arrows) in descending aorta.
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Fig. 12A. 48-year-old man with penetrating atherosclerotic ulcer. Axial
double-inversion-recovery MR image (TR/TE, 1017/20; inversion time, 150 msec)
shows intermediate-signal-intensity eccentric intramural hematoma in distal
thoracic aorta (arrow).
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Fig. 12B. 48-year-old man with penetrating atherosclerotic ulcer. Axial
double-inversion-recovery MR image (1017/20; inversion time, 150 msec) shows
distinct ulcer crater with signal void (arrow).
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Fig. 12C. 48-year-old man with penetrating atherosclerotic ulcer.
Contrast-enhanced spoiled gradient-refocused echo source MR image (3.7/1.3;
flip angle, 30°) shows ulcer crater (arrow) filling with contrast
material.
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Fig. 12F. 48-year-old man with penetrating atherosclerotic ulcer. Axial CT
scan obtained below ulcer crater level shows intramural hematoma
(arrow), compatible with aggressive behavior of lesion.
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Fig. 13A. 83-year-old man with chronic obstructive pulmonary disease and
hypertension. Contrast-enhanced CT scan shows calcified atheromatous plaque
with focal ulceration (arrow) but without contrast extravasation
beyond plaque.
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Fig. 13B. 83-year-old man with chronic obstructive pulmonary disease and
hypertension. Axial CT scan shows plaque-related intraluminal irregularity
(arrow), but no contrast material is extending beyond level of intima
(marked with calcification) and no intramedial hematoma is present.
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Summary
Patients presenting with acute aortic syndromes usually have a similar
clinical profile: aortic pain with coexisting history of hypertension.
However, the pathophysiology and appearance of these syndromes differ in many
ways. The classic aortic dissection involves an intimomedial flap, which
traverses the aortic lumen. Intramural hematoma and penetrating aortic ulcer
are nonflap lesions, with intramural hematoma showing no intimal disruption
and penetrating aortic ulcer showing an ulcer at the atherosclerotic plaque
burrowing through the aortic intima and media. Radiologic evaluation plays a
key role in assessing patients with acute disease of the aorta, and imaging
techniques should aim both to diagnose the condition and to characterize the
underlying pathology.
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