114
consequences of false-positive and particularly of false-negative re-
sults. There have been a number of studies carried out over the
past two decades comparing CTA, MRA, TEE, and aortography for
the diagnosis of aortic dissection, and a recent meta-analysis by
Shiga et al.
122
showed that CTA, MRA, and TEE are all outstanding,
with sensitivities of 98% to 100%, as shown inFigure23. On the
other hand,aortographyhas asensitivityof only88%, perhapsreflect-
ing the fact that IMH often goes undetected with this technique. In
the same meta-analysis, the specificity of the four imaging modalities
was roughly equivalent at 94% to 98%, as shown in Figure 24.
Therefore CTA, MRA, and TEE are all reasonable first-line imaging
studies to choose for this purpose.
It is important to note, however, that the research studies that
evaluate the accuracy of imaging modalities are usually performed
at centers of excellence and interpreted by designated experts in
aortic imaging, and it is thereforereasonableto suspect thataccuracy
may be lower when the same imaging modalities perform in the
‘‘real-world’’ setting. Indeed, a report from the International
Registryof AcuteAorticDissection (IRAD)examined this veryques-
tion, and theresults are shown inFigure25.
120
Thereal-world sensi-
tivity of both CTA and TEE is lower than in theabovemeta-analysis,
probably reflecting a lesser degree of expertise among the readers.
Interestingly, the real-world sensitivity of MRA remained at 100%,
which may reflect the fact that MR angiograms tend to be read by
specialists (e.g., vascular radiologists) rather than generalradiologists
(e.g., emergency department radiologists). The diagnostic and prac-
tical features of each of the five common imaging modalities are
summarized inTables4and5.
III. ACUTE AORTIC SYNDROMES
A. Introduction
The term AAS
128
refers to the spectrum of aortic pathologies,
including classic aortic dissection, IMH, penetrating aortic ulcer
(PAU), and aortic aneurysm rupture (contained or not contained).
Although the pathophysiologyoftheseheterogeneous conditions dif-
fers, they are grouped because they share common features: (1)
similar clinical presentation (‘‘aortic pain’’), (2) impaired integrity of
the aortic wall, and (3) potential danger of aortic rupture requiring
emergency attention.
128-133
Moreover, some of these conditions
may represent stages in the evolution of the same process. We have
elected not to include, as some authors do, aortitis and traumatic
aortic rupture, because they have totally distinct clinical and
pathophysiologic profiles.
128
Clinical databases, such as the IRAD,
have contributed tremendously to our knowledge of these acute
aortic pathologies.
134
Becauseof the life-threatening nature of theseconditions, prompt
and accurate diagnosis is paramount. Misdiagnosis of these condi-
tions, usually because of confusion with myocardial ischemia, can
lead to untimely deaths.Table6 lists some less urgent conditions
that can potentially mimic AAS.
Thenoninvasiveimaging techniques that playa fundamentalrole
in thediagnosis and managementof patientswith AASincludeCTA,
TTE, TEE and MRI. Some patients may require more than one
noninvasive imaging study and, in rare instances, invasive aortog-
raphy may be necessary. Imaging is used to confirm or exclude
the diagnosis, determine the site(s) of involvement, delineateexten-
sion, and detect complications to plan themost appropriatemanage-
ment approach.
B. Aortic Dissection
1. Classification of AorticDissection. Accurate classification of
aortic dissection is important because significant differences in clin-
ical presentation, prognosis, and management depend on the loca-
tion and extent of the dissection. . Figure 26 illustrates the two
commonly used classifications: the DeBakey system (types I, II,
and III)
124,125
and the Stanford system (types A and B).
126
Dissections involving the aortic arch without involving the
ascending aorta are classified as type B in the Stanford system.
The majority of dissections, whether type A or type B, propagate
beyond the diaphragm to the iliac arteries.
The appropriate management of aortic dissections depends not
only on the location of the dissection but also on the time that has
elapsed between onset of the process and the patient’s presentation.
Although the adjectives acute, subacute, and chronic areoften applied,
thereisno standard definition for these timeperiods.
135-138
Thereis a
24-hour ‘‘hyperacute’’ period during which dissections involving the
ascending aorta carry a risk for rupture approaching 1% per hour.
Studies have shown that 75% of aortic dissection–related deaths
occur in the initial 2weeks. At the opposite extreme are ‘‘old dissec-
tions’’ encountered incidentally during aortic imaging or surgery.
These are clearly ‘‘chronic.’’ Hirst et al., Levinson et al., and DeBakey
considered an aortic dissection to be ‘‘acute’’ when the onset of
Figure 26 6 Diagramillustratingthetwocommonlyusedclassifi-
cation systems for aortic dissection. Inthe older of the two, the
DeBakey system, type I dissection originates in the ascending
aorta and propagates distally to includes at least the arch and
typically the descending aorta. Type II dissection, not shown
(the least common type) originates in and is confined to the
ascendingaorta. Type IIIdissectionoriginatesinthe descending
thoracic aorta(usually justdistaltotheleftsubclavianartery)and
propagates distally, usually to below the diaphragm. The Stan-
ford system, in a simpler scheme, divides dissections into two
categories: those that involve the ascending aorta, regardless
of the site of origin, are classified as type A, and those beginning
beyond the archvesselsare classifiedastype B. The majority of
dissections, whether type A or type B, propagate beyond the
diaphragm to the iliac arteries.
138 Goldstein et al
Journal of the American Society of Echocardiography
February 2015
