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62 Danias
DISCUSSION AND COMMENTARY
Questions for the Author
The ordering of aortic imaging studies can be confusing. How do we know when
to order contrast or non-contrast studies (or both), CT scan or CT angiogram,
MR scan, or MR angiogram? When should we order 3-D reconstructions? Can
these always be regenerated from the basic study, if required? Does the creation
of 3-D formulations still require major input from the technician, or is this fully
automated now?
Ordering of aortic imaging studies can be quite confusing. Even more compli-
cated is the ordering situation with MRI, because the terminology of the various
sequences and the imaging characteristics differ among vendors and users.
However, some general principles may be kept in mind when ordering imaging
aortic studies. The three major factors that determine which test should be ordered,
and when, for a particular suspected aortic pathology are: (i ) the acuity of the
situation (ii) the availability of each modality, and (iii) the presence of comorbidi-
ties. In general, for known or suspected aneurysms, noncontrast CT or MRI studies
are usually adequate. For suspected or known dissections or vessel wall ulcerations,
TEE or contrast enhanced CTA or MRA are indicated. If vessel wall rupture is
suspected, contrast enhanced CT or MRI would be the preferred modalities.
It is important to recognize that the inherent tissue contrast in non-contrast
enhanced studies is not high enough to allow for digital (post-processing)
separation of the aorta from the surrounding structures. Thus 3-D reconstructions
can only be obtained with contrast-enhanced studies (be they CTA or MRA).
It generally takes a short time (a few minutes) for a trained technician to create a
3-D model of the aorta and its main branches. Operator skill is important because
it is easy artifactually to eliminate useful information and also to introduce arti-
facts by excessive subtraction of background tissues. This is why clinical interpreta-
tions should never be based on 3-D reconstructions alone. In general 3-D
reconstructions do not add diagnostic value to a CTA or MRA. The main value of
these representations is to more effectively transfer information to the nonimaging
specialist, because 3-D reconstructions obviate the need to mentally integrate the
2-D information into a volume image. Thus, the 3-D images help the clinician to
better appreciate the anatomic relationships of the aorta with other adjacent struc-
tures. In this context, it is frequently helpful to ask for 3-D reconstructions,
although the focus should never be on just a pretty image.
As a final note, personal contact and discussion with the imaging specialist
regarding the value of each modality for any particular patient should be encour-
aged. The clinical history is very helpful in guiding the imager. Also, intermediate
or equivocal findings may be better assessed in the context of the clinical
presentation via discussion between radiologist and clinician.
Are there prospects for increasing beyond the 64-slice CT scanning machines
currently coming into widespread use? Can we expect 128- or 256-slice machines
and studies?
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Imaging of Aneurysms and Dissections 63
Imaging technology advances at a rapid pace. Over the last few years, CT technol-
ogy has evolved from single slice to spiral to multislice technology, and the
number of detectors in multislice scanners has increased from 4 to 16 to 64. One
hundred and eight- and 256-slice scanners are in development and likely to be
in clinical practice soon. With the increasing number of detectors, one issue of
concern is that radiation exposure increases proportionately. With the 64 detec-
tors, the absorbed radiation dose for a cardiac study is ∼11 mSv, almost double
that of a 16-slice scanner (Reference 18, above). This may in fact become a
limiting factor in the widespread applicability of scanners with higher number
of radiation detectors.
A different approach to conventional CT imaging is represented in the
so-called flat-panel technology. This approach does not use rotating detectors but
rather a flat detecting surface that allows for volumetric high-resolution imaging.
Preliminary application of this technology has been reported for imaging of the
coronary arteries in an excised swine heart (1). At the present time, the computing
power needed for in vivo cardiovascular imaging is not practical, although in the
future computer technology may surpass this frontier.
Do you anticipate that in the future interventional vascular procedures can be
performed under “CT fluoro,” obviating the need for angiographic control of
these procedures?
Currently, interventional vascular procedures are performed under fluoroscopy. One
drawback of this approach is the considerable radiation exposure. CT fluoroscopy,
at least with current technology, could potentially facilitate the three-dimensional
appreciation of the inter-relationships of the anatomic structures visualized during
interventional procedures. CT guidance, however, would not eliminate the radia-
tion exposure, and in fact the radiation dose would likely be higher than the cur-
rent projection angiographic approach. On the other hand, real-time MR guidance
would be a significant advance, as this would eliminate ionizing radiation expo-
sure. Catheters equipped with receiver coils at tip have been developed and shown
to be adequately imaged at a rate of a few frames per second. MR advancement of
catheters in the aorta of experimental animals has been shown to be possible (2),
and even feasibility data in peripheral arterial interventions in humans have been
described (3). Because of the minimal biologic cost that this approach offers, it is
likely that this technology will become a clinical tool in the not too distant future.
Are there any totally new imaging modalities on the horizon, different from CT
or MR?
Technology advances at a rapid pace. Over the last decade we have witnessed a
shift from macro-anatomical imaging to micro-molecular and cellular imaging.
Developments have focused more on coronary atherosclerosis, as this is the major
cause of morbidity and mortality in humans. These developments, however, can
be applied to the entire vascular tree, where atherosclerosis can develop.
Newer technologies that attempt to assess the atherosclerotic plaque include
thermography, angioscopy, spectroscopy, elastography, and optical coherence
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64 Danias
tomography, among others. Excellent reviews of these new technologies have
recently been published (4,5). Positron-emission-tomography (PET) has also been
reported to visualize atherosclerotic plaque by way of selective FDG uptake at the
vessel wall. This may be an indicator of increased metabolic activity at the plaque,
and may carry additional prognostic information (6,7).
Finally combination technologies are now being developed, whereby anatomic
information is merged to functional-metabolic data. The most commonly used
such technology is PET-CT, although PET-MRI, ultrasound-MRI and X-ray-MRI
systems have been or are being developed. It is certain not only that the techno-
logical developments in the years to come will allow us to accurately evaluate
the anatomic macroscopic appearance of the cardiovascular system, but also to get
insights into the pathophysiologic mechanisms of cardiovascular disease that can
lead to more targeted therapeutic approaches.
References
1. Knollmann F, Pfoh A. Image in cardiovascular medicine. Coronary artery imaging with
flat-panel computed tomography. Circulation 2003; 107(8):1209.
2. Bock M, Volz S, Zuhlsdorff S, et al. MR-guided intravascular procedures: real-time
parameter control and automated slice positioning with active tracking coils. J Magn
Reson Imaging 2004; 19(5):580–589.
3. Dick AJ, Raman VK, Raval AN, et al. Invasive human magnetic resonance imaging:
feasibility during revascularization in a combined XMR suite. Catheter Cardiovasc
Interv 2005; 64(3):265–274.
4. Pasterkamp G, Falk E, Woutman H, Borst C. Techniques characterizing the coronary
atherosclerotic plaque: influence on clinical decision making? J Am Coll Cardiol 2000;
36(1):13–21.
5. Davies JR, Rudd JH, Weissberg PL. Molecular and metabolic imaging of athero-
sclerosis. J Nucl Med 2004; 45(11):1898–1907.
6. Tatsumi M, Cohade C, Nakamoto Y, Wahl RL. Fluorodeoxyglucose uptake in the aortic
wall at PET
/
CT: possible finding for active atherosclerosis. Radiology 2003;
229(3):831–837.
7. Okane K, Ibartaki M, Toyoshima H, et al. 18F-FDG accumulation in atherosclerosis:
use of CT and MR co-registration of thoracic and carotid arteries. Eur J Nucl Med Mol
Imaging 2006; 33(5):589–594.
Editor’s Counterpoint
Dr. Danias, in his superlative review of diagnostic imaging in aortic diseases,
gently impugns the utility of the plain chest x-ray in thoracic aortic aneurysm and
dissection. The Editor respectfully takes issue with this, believing that the plain
film contributes immensely to the early diagnosis of aneurysm and dissection.
The plain chest x-ray shows the contours of the thoracic aorta quite well,
given the contrast between the air-filled lungs and the fluid-filled aorta. The normal
contours of the aorta are quite familiar and generally very well seen (Figs. A and B).
The ascending aorta, if substantially enlarged, will appear outside the upper right
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Imaging of Aneurysms and Dissections 65
Figure A (1) Normal chest x-ray. (2) Same chest x-ray, with areas where ascending, arch,
and descending aortic aneurysm shadows may appear.
Figure B Aneurysms diagnosed by CXR. (1) Ascending; (2) arch; (3) descending.
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66 Danias
cardiac silhouette. The aortic knob should normally be small and distinct. This
knob will enlarge in case of arch aneurysm and become indistinct in patients with
aortic dissection. The descending aorta normally makes a clean, crisp stripe to the
left of the vertebral column. Aneurysmal dilatation of the descending aorta will be
clearly seen, with bulging of this stripe to the right.
Of course, Dr. Danias’ erudite comments are very well taken. In the current
era, three-dimensional imaging with echocardiography, CT scanning, or MRI
imaging will provide precise anatomic information about an aneurysm suspected
on chest x-ray. On the Editor’s aortic service, however, we strive hard to
encourage residents trained entirely in the CT/MR era not to ignore the chest
x-ray; the plain film can, upon careful reading, not only raise the suspicion of aortic
disease, but also predict, with surprising accuracy, the findings that will obtain on
more advanced imaging modalities.
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67
4
Putting It All Together: Symptoms,
Signs, and Images
Arun Raghupathy and Kim Eagle
Division of Cardiovascular Medicine, University of Michigan,
Ann Arbor, Michigan, U.S.A.
Pain attending the splitting of the aortic wall is usually excruciating and
extensive, radiating from midthorax front or back through the chest, down
the back, and even into the thighs or up into the neck. The pain in the
thorax or back comes suddenly at its maximum and is often prostrating,
inducing a state of shock or even death.
—Paul Dudley White, 1944
INTRODUCTION
Acute aortic dissection is a cardiovascular emergency associated with high mor-
tality, and successful outcomes depend on the rapid recognition of the clinical
symptoms and signs associated with this condition (1–5). Modern imaging modal-
ities can precisely define a spectrum of aortic pathologies, but they are clinically
useful only when patients are accurately identified in a timely fashion so that
treatment can be delivered promptly. Therefore, the astute clinician must know
how to quickly incorporate key elements from the symptoms, signs, and images
in order to confirm the diagnosis and initiate appropriate therapy for this
life-threatening disease.
Keeping this in mind, this review will discuss our current understanding of
the clinical presentation of this complex yet fascinating disease. Compared to
other cardiovascular emergencies, such as stroke and acute myocardial infarction,
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68 Raghupathy and Eagle
the incidence of aortic dissection is quite rare, with an estimated range of 5 to
30 cases per million persons per year (1). As such, clinical observations pertaining
to acute aortic conditions, although valuable, are often limited by the naturally
smaller sample sizes found in single-center case series. In contrast, much of our
current and expanding body of knowledge derives from our experience with the
International Registry of Aortic Dissection (IRAD). Since its inception in 1996,
this ongoing, worldwide multi-institution research collaboration among special-
ized aortic referral centers has collected important clinical data on over 1350
consecutive patients to gain insight into the clinical presentation, management,
and outcomes of acute aortic conditions.
This chapter is designed to equip the triaging clinician with the essential
information required to develop a practical and efficient diagnostic approach to
the patient with an acute aortic condition. Speed in appropriately suspecting and
confirming the diagnosis is a recurring theme echoed throughout this discussion,
as severe, often catastrophic complications tend to develop quickly. From the time
of symptom onset, mortality in untreated (or undiagnosed) acute dissection rises
rapidly with each passing hour, approaching 50% in the first 24 hours (6,7). Early
mortality is usually the result of a ruptured aorta, manifesting clinically as cardiac
tamponade or frank exsanguination. Serious morbidity, including multisystem
organ failure, may result from occlusion of the aortic branches, with resultant
malperfusion to vital organs such as brain, kidney, spinal cord, and limbs.
Therefore, the importance of prompt action and maintaining a high index of
suspicion to minimize diagnostic delays cannot be overemphasized.
PREDISPOSING FACTORS
The initial approach to evaluating the patient suspected of having an acute aortic
condition begins with recognizing the constellation of high-risk conditions that are
associated with the disease. A summary of such predisposing conditions is listed in
Table 1. Hypertension exists in up to 72% of patients and is by far the most common
feature. Advanced age is another common characteristic, with a mean age of dis-
section occurring in the seventh decade of life (1,8). Among younger patients
(age <40), hereditary connective tissue disorders, such as the Marfan’s syndrome
or bicuspid aortic valve, play a larger role than long-standing hypertension (5,9).
Men are twice as likely as women to suffer an acute aortic dissection. However,
women tend to present with dissection at older ages, with nearly half of women
presenting at age >70 years old. Contrary to previous reports from case studies, our
experience with IRAD suggests that pregnancy is only rarely associated with acute
dissection, unless it co-exists with the Marfan’s syndrome and an aortic root diam-
eter >40 mm (1,10). Prior cardiovascular intervention, including surgical or cathe-
ter instrumentation of the aorta, is an important feature found in 4% to 5% of
patients with Type A or Type B dissection. An even greater association is seen in
patients presenting with Type A dissection, where a history of recent or prior
cardiac surgery is present in approximately one of every six patients (11,12).
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Putting It All Together: Symptoms, Signs, and Images 69
SYMPTOMS
Typical Symptoms
Because dissection may present with a broad range of symptoms, it is essential for
the clinician to maintain a high index of suspicion for acute aortic syndrome when
evaluating any patient who carries the usual predisposing risk factors (Table 1).
From our experience with IRAD, the single most reliable presenting symptom in
patients with acute dissection is the sudden onset of severe pain localized to the
anterior chest or back, and less often, the abdomen. Contrary to classic teaching,
patients are more likely to describe the quality of pain as sharp, as opposed to
tearing or ripping. Moreover, the abrupt onset of pain seems to be the most
frequent and consistent characteristic, as it is reported in 85% of both Type A and
Type B aortic dissections (1). The sudden onset of severe pain is typically dramatic
enough that patients often describe the details of the inciting event with a pinpoint
or “freeze-frame” accuracy (13). A pattern of recurrent or stuttering pain should
alert the clinician to the potential progression of an unstable aortic lesion such as
penetrating aortic ulcer or intramural hematoma into overt dissection (Fig. 1)
(4,14–21). The location of pain may sometimes be helpful in distinguishing Type
A from Type B aortic dissection, but this type of assessment should be regarded as
nonspecific. In general, pain localized to the back or abdomen is more consistent
with Type B dissection, whereas patients with Type A dissection usually localize
pain to the anterior chest (Table 2) (1,22,23).
Table 1 Predisposing Factors for Acute
Aortic Conditions
Hypertension
Advanced age
Atherosclerosis
Smoking
Cocaine or amphetamine use
Male gender
Connective tissue disorders
Marfan’s syndrome
Ehler’s Danlos syndrome
Aortic coarctation
Bicuspid aortic valve
Vascular inflammation
Giant cell arteritis
Takayasu arteritis
Syphilis
Iatrogeni
Catheter instrumentation of aorta
Prior or recent cardiac surgery
Aortic cross clamping/aortotomy
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70 Raghupathy and Eagle
Syncope occurs in 5% to 10% of patients with dissection, and is nearly
always unique to Type A dissection. In this setting, it may herald serious hemo-
dynamic compromise, as seen in cardiac tamponade and stroke. Mechanisms for
syncope in dissection are diverse and vary based on the location and extent of the
dissection. For example, rupture into the pericardium may produce tamponade
physiology or dissection of the carotid arteries may lead to stroke with cerebral
hypoperfusion. Severe pain, hypovolemia, or an exaggerated aortic baroreceptor
response due to stretching of the aortic wall are other possible mechanisms
(2,3,13,24). A small percentage (up to 3%) of patients with dissection will have
syncope without prior back or chest pain (24), highlighting the importance of
recognizing atypical presentations, as discussed in the following section.
Atypical Symptoms
Although the abrupt onset of thoracic pain is not difficult to elicit by history,
not all patients with an acute aortic condition will present in this classic manner
(Table 3). Atypical clinical symptoms, with asymptomatic or nonlocalizing pain,
are most often seen in female patients, the elderly, and those with prior cardiovas-
cular surgery (8,10,12). When compared to men, women are less likely to have
pain on presentation (10). The elderly tend to present with unexplained syncope
and neurological deficits (8). Such challenging variations in symptoms may in part
explain why the diagnosis of acute dissection is only suspected in as few as 15%
to 43% of patients presenting acutely (6,25). Furthermore, the subset of patients
Table 2 Typical Symptoms of Acute Aortic Dissection
All (%) Type A (%) Type B (%) P-value
Pain 92.9 91.5 95.2 0.001
Abrupt 85.1 84.8 85.5 NS
Anterior 65.9 72.2 55.7 <0.001
Back 52.8 44.2 66.7 <0.001
Abdominal 28.0 23.1 36.0 <0.001
Sharp 80.4 78.9 82.7 NS
Tearing 72.8 71.6 74.6 NS
Syncope 13.1 18.8 3.9 <0.001
Figure 1 Spectrum of acute aortic conditions. Source: From Ref. 47.
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Putting It All Together: Symptoms, Signs, and Images 71
with atypical presentations will often present later in the natural course of dissec-
tion and are at high risk for hemodynamic derangement, malperfusion, and death
if the diagnosis is missed or further delayed (2,23).
Therefore, it is imperative for the clinician to recognize patients who
are more likely to present atypically and aggressively pursue the diagnosis of an
acute aortic condition in any patient who presents with unexplained hypoperfusion
to an end organ or extremity. Symptoms consistent with end-organ malperfusion
may include abdominal pain, neurological deficit due to ischemia of the
spinal cord, limb ischemia, and renal failure. The specific symptom complex
may help localize the anatomic extent of the dissection along the aorta and its
major branches.
In IRAD, up to 6.4% of patients denied any pain on presentation, consistent
with the 5% to 15% incidence, reported in the literature. When compared to
patients who describe pain on presentation, these patients are significantly more
likely to have syncope, congestive heart failure, stroke, and in-hospital death.
Alarmingly, patients presenting without pain had a median time of 29 hours
for diagnosis versus 10 hours in those who presented with typical pain. Painless
aortic dissection is more common in the elderly patients with existing aortic
aneurysms, prior cardiovascular surgery, and diabetics (8,10,12,26). Women
are more likely than men to have painless aortic dissection (10). Mechanisms of
painless aortic dissection are poorly understood, but may be related to conditions
in which the aorta dissects gradually or in some manner spares the richly
innervated adventitia. Prior cardiovascular surgery and surgical aortic mani-
pulation may also alter the patient’s perception of aortic pain, and diabetics
may be vulnerable to painless dissection due to denervation of perioaortic pain
receptors (12,26,27).
Another atypical presentation is that of acute aortic dissection manifesting
in a patient who presents with a primary or isolated complaint of abdominal
pain. This challenging presentation was reported in approximately 5% of patients
in IRAD, and each patient was ultimately diagnosed with acute Type B aortic
dissection. Although relatively rare, patients presenting in this manner had signifi-
cantly higher rates of in-hospital death when compared to patients with more
typical symptoms.
Table 3 Atypical Symptoms inAcute Aortic Conditions in Different Patients
Patients at risk for presenting with Atypical symptoms of acute
atypical symptoms aortic conditions
Elderly (age >70) Painless acute aortic condition
Female Abdominal pain
Diabetic Syncope
Existing aortic aneurysm Altered mental status
Prior cardiovascular surgery Stuttering, recurrent pain
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