Imaging of Acute Aortic Syndrome: Advantages ...€¦ · of acute aortic syndrome, so it is the first one performed. It can only shed light on some cases of AAS, concerning aortic

(Hellenic Journal of Cardiology) HJC • 169

Hellenic J Cardiol 2015; 56: 169-180

Review ArticleReview Article

Manuscript received:December 21, 2013;Accepted:September 17, 2014.

Address:Nikolaos A. Papakonstantinou

12 Zilon St.111 42 RizoupoliAthens, [email protected]

Key words: Aortic dissection, intramural hematoma, penetrating atherosclerotic ulcer.

Imaging of Acute Aortic Syndrome: Advantages, Disadvantages and PitfallsEfstratios apostolakis1, Nikolaos a. papakoNstaNtiNou2, Nikolaos G. Baikoussis3, aNastasios pEtrou4, JohN GoudEvENos5

1Cardiothoracic Surgery Department, University Hospital of Ioannina, School of Medicine, Ioannina, 2General Surgery Department, General Oncology Hospital of Kifissia “Agioi Anargyroi”, Kifissia, Athens, Greece; 3Cardiac Surgery Department, L’Institut Mutualiste Montsuris, Paris, France; 4Department of Anesthesia and Postoperative Intensive Care, 5Department of Cardiology, University Hospital of Ioannina, Ioannina, Greece

A ccording to Vilacosta et al,1 acute aortic dissection, intramural he-matoma, and penetrating athero-

sclerotic ulcer of the aorta constitute 3 heterogeneous clinical entities that com-pose the so-called acute aortic syndrome (AAS). Although inflammatory diseases of the aorta (aortitis) and its traumatic rupture are not included in this syndrome because of their different pathophysiologi-cal and clinical pictures, we believe that every aortic emergency or aortic compli-cation requiring an urgent intervention should be considered to be an expression of acute aortic syndrome. The reason why we maintain this opinion is the fact that inflammatory diseases of the aorta and aortic rupture, compared to the former clinical entities, are characterized by simi-lar symptoms (chest pain and blood pres-sure alterations), they are diagnosed us-ing the same diagnostic tools, and they are treated in the same way (either surgical or endovascular treatment).

The “key’’ to the differential diagnosis among several thoracic emergencies is im-aging itself. In case of an aortic emergency, we are interested in knowing the type and extent of the injury, its exact location, pos-sible consecutive complications and the ap-propriate treatment.2-4 The scope of this

review is the exploration of the role of each diagnostic tool in acute aortic syndrome. The imaging armamentarium includes chest X-ray, transthoracic and transesoph-ageal echocardiography (TTE and TEE), computed tomography (CT), magnetic res-onance (MRI), and aortography.

Plain chest radiography

A chest X-ray is our cheapest and simplest imaging diagnostic tool in the diagnosis of acute aortic syndrome, so it is the first one performed. It can only shed light on some cases of AAS, concerning aortic an-eurysms, acute aortic dissection, or trau-matic aortic rupture. However, it is able to show pathological elements in just 60-90% of cases of aortic dissection and a normal chest X-ray does not exclude aortic dissec-tion.5 Furthermore, it presents very low sensitivity, of the order of 64%, in the di-agnosis of AAS,3,6,7 given that mediastinal tumors, cardiopathies or lung diseases ap-pear in the same way on chest radiogra-phy.8 Therefore a chest X-ray is associat-ed with poor diagnostic value in the case of AAS. Von Kodolitsch et al3 reported 64% sensitivity and 86% specificity when studying the diagnostic value of the X-ray in 216 patients with suspected AAS. The

170 • HJC (Hellenic Journal of Cardiology)

E. Apostolakis et al

sensitivity was 67% in cases of acute aortic dissection, 61% in cases of non-dissected aortic aneurysm and 63% in cases of penetrating atherosclerotic ulcer. It is remarkable that a lower sensitivity (63%) was related to the ascending aorta compared to the 77% sensitiv-ity concerning the aortic arch and descending aorta.

Mediastinum widening, double aortic contrast and discrepancy between the diameters of the ascend-ing and descending aorta are typical radiological fea-tures of acute aortic dissection. According to the In-ternational Registry of Aortic Dissection (IRAD),5 63% of patients experiencing acute aortic dissection type A and 56% with type B aortic dissection present mediastinal widening, whereas 11% of patients with type A aortic dissection and 16% with type B have a normal chest X-ray. A recent retrospective study evaluating the diagnostic value of an anomalous aor-tic contour and pleural effusion in plain chest radiog-raphy concerning the diagnosis of acute aortic dissec-tion reported a 71% sensitivity of X-rays for the for-mer feature but a 16% sensitivity for the latter.9

In contrast, the negative predictive value of a nor-mal chest X-ray in cases of aortic rupture reaches 98%.10 An anomalous aortic notch, upper mediasti-nal widening, displacement of the trachea and of the left main bronchus, imprecision of the aorto-pulmo-nary window, an apical cap on the left lung, pleural effusion, and widening of the left paravertebral sulcus are the typical features of aortic rupture in a chest ra-diograph.6,11 Finally, its sensitivity in the diagnosis of either an intramural hematoma or a penetrating ath-erosclerotic ulcer is extremely poor, providing only indirect data, such as calcification of the aortic notch, aortic tortuosity and distension.3

Transesophageal or transthoracic echocardiography

TTE is a cheap, safe and easily repeated diagnostic tool that is rapidly performed (within 8-10 minutes) and can be carried out even next to the patient’s bed or in the emergency room.6 Its major advantage, com-pared to other imaging tools, is its ability to simulta-neously evaluate cardiac valves as well as myocardial reserves (Table 1).6 Furthermore, hemodynamically unstable patients can undergo TTE, whereas CT or MRI cannot be performed.8 However, the patient’s body structure has a noticeable impact on its sensi-tivity and for this reason TEE is more advantageous, especially in cases of acute aortic dissection. Thus, according to IRAD, TEE, which is performed in 28-33% of cases, constitutes the second most used diag-

nostic tool following the chest CT.2,12 Although TTE can reliably explore the aortic root, the ascending aorta and the aortic arch, it cannot image either the distal ascending aorta or the descending aorta, where as TEE cannot explore in detail either the ascend-ing aorta, because of the right main bronchus, or the proximal aortic arch, because of the trachea.8

The disadvantages associated with the perfor-mance of TEE are its invasiveness, its need for light sedation, the fact that it is operator-dependent, and that patients suffering from esophageal diseases can-not undergo the examination (Table 1).8,12,13 More-over, we should not underestimate the mortality re-lated to TEE, which is extremely low, but not so low as the relevant literature reports.6 Sedation, hyper-tension, bradycardia and rupture are potential com-plications, in light of which IRAD suggests that TTE should be performed first; if it is positive, we can then proceed to perform TEE for confirmation.2,12

The sensitivity of this imaging method depends on the operator’s experience and on the cause of AAS. Acute type A aortic dissection is associated with 77-80% sensitivity and 93-96% specificity.8,14 Ac-cording to other studies, the sensitivity of TEE reach-es 90-95% and its specificity 95% with regard to the proximal aorta; however, as far as the distal aorta (distal descending or abdominal aorta) is concerned, its sensitivity is limited to 70-80%.2,15 Moreover, TEE is also invaluable in the diagnosis of intramural he-matoma of the aorta, having 95% sensitivity and 90% specificity in expert hands.16

The presence of a mobile intimal flap within the aortic lumen is pathognomonic for the diagnosis of acute aortic dissection (Figures 1 & 2).8,13 Total ob-struction of the false lumen, the presence of throm-bus in the aortic wall, central displacement of calcifi-cations, and local dyskinesia of the aortic wall during systole constitute some other indications of acute aor-tic dissection.8 Systolic dilatation and diastolic coap-tation, intense flow, a systolic jet being directed away from the aortic lumen, and systolic blood propagation are the features on which TEE bases its identification of the true lumen, although this can be quite difficult (Figure 3). On the other hand, the typical features of the false lumen are a diastolic increase in aortic di-ameter, spontaneous echo contrast, delayed or retro-grade flow, and the presence of thrombus.8

In cases of intramural hematoma and penetrat-ing atherosclerotic ulcer, the sensitivity and specificity of ΤΕΕ strongly depend on the operator’s experience and on a high index of suspicion.17,18 Aortic wall thick-


Imaging of Acute Aortic Syndrome

ness17-19 and a local crater, especially in highly athero-matous regions or in regions having a thickened wall, are the features we seek in order to diagnose intramu-ral hematoma or penetrating atherosclerotic ulcer.18 The current literature reports 98% sensitivity and a 95% specificity.20,21 The “pitfall’’ of TTE and TEE is their inability to distinguish an atheromatous plaque from an intramural thrombus (Table 1).21 Indirect find-ings, such as displaced intimal calcifications of the aor-tic wall, may give some help towards this direction.21

In contrast, TTE, and TEE even more, are high-sensitivity diagnostic imaging tools in the case of trau-matic rupture of the aorta. There are three potential types of echo picture: a linear intimal tear of the endo-

thelium; a deeper tear, including the tunica media of the aorta; or a total, subadventitial rupture of the aor-tic wall.22 Generally, TEE constitutes a valuable imag-ing tool in the diagnosis of aortic rupture, from a sim-ple linear tear undergoing conservative treatment to a subtotal rupture requiring surgical treatment, because it can be performed even in intubated patients in the emergency or the operating room. Its sensitivity rang-es from 57% to 100% and its specificity from 84% to 100%, depending on the operator’s experience.22

Computed tomography or multidetector computed tomography

CT of the thoracic aorta is a safe and noninvasive im-aging procedure which, although taking only a few minutes, constitutes a precise and reliable diagnos-tic tool as far as AAS is concerned.2,12,23 Accord-ing to IRAD, it is for these reasons that CT is the most commonly used diagnostic tool in the diagnosis of this syndrome and the determination of the best treatment.5,24 However, artifacts due to respiration and heartbeats may be interposed in a conventional CT image. Therefore, fast CT scanning (CT angiog-raphy), which eliminates all these artifacts, may be performed to increase the reliability of the diagno-sis.18,25 Moreover, the development of multislice CT (MSCT) or multidetector CT (MDCT), which are characterized by minimum sections of 1 mm, has de-creased the time required and provides both higher image resolution and fewer artifacts.26 Consequent-ly, MDCT is the imaging test of choice in the diagno-sis of AAS, having sensitivity and specificity of almost 100%.7 Additionally, the introduction of machines with 64- and 128-row detectors and the ECG-gating modification (ECG-gated MDCT) permit the avoid-ance of artifacts due to cardiac and respiratory func-tion.3,4,27,28 Indeed, artifacts are produced in 90% of non-ECG-gated MDCT images, especially in the aor-tic root.5,6,15,29 Alternatively, a retrospective analysis and reconstruction of the image, isolating R-R seg-ments—which present the minimum myocardial func-tion and motion—can be performed.6,27,29

The diagnosis of acute aortic dissection is based on the identification of the intimal flap and on the dis-tinction between the true and the false lumen. The diagnostic features that help to distinguish between the two lumens are given in Table 2. MDCT can eas-ily identify all the typical features of acute aortic dis-section: the intimal flap, the false and the true lumen (Figures 4 & 5), the condition of the aortic branches

Figure 1. Transesophageal echocardiography. A dissecting aortic aneurysm with the “flap” (arrow) visible at the sinuses of Valsalva. The distortion of the anatomy at the aortic ring leads to aortic insufficiency.

Figure 2. Transesophageal echocardiography. A short-axis view of the dissecting aneurysm in the ascending aorta. The arrow indi-cates the false lumen.



involved (Figure 6), the anatomy of the proximal coro-nary arteries, the presence of pericardial effusion (Fig-ure 4), and the ischemia of several organs.8,25,26 At the same time, it provides information about the extent of the injury along the entire thoracic aorta (Figure 5).30

Finally, it has a prognostic role in the evolution of aor-tic dissection, based on the relevant findings.31

In non-contrast MDCT, intramural hematoma appears either as a local semilunar thickening of the aortic wall, or as localized thickening of the aortic

Table 1. Advantages, disadvantages and pitfalls of imaging methods used in the diagnosis of acute aortic syndrome.

Diagnostic tool Efficacy

Chest X-ray

Advantages • low radiation dosage• performance in the emergency room27

• very high negative predictive value of normal chest radiography in case of aortic rupture10

Disadvantages • low specificity3,5,6

• low sensitivity in the diagnosis of aortic diseases3,27

• unreliable in case of cardiac or pulmonary diseases7,27

• unreliable when it is normal (in order to exclude)5,6

Pitfalls • false positive in cases of aortic tortuosity and when a mediastinal tumor, pleural effusion or heart failure is present6,7

TTE or TEE

Advantages • without radiation burden27

• very high sensitivity and specificity (95-98%) in all cases of AAS20,21

• simultaneous investigation of aortic valve and cardiac function13,20,21

Disadvantages • an expert operator is required8,12,27

• time-consuming13,21

• related to complications such as sedation, hypertension, bradycardia, rupture2,6,12

• cannot be performed in the emergency room27

• semi-invasive method13

• mild sedation is required8,13

• contraindicated in patients with esophageal diseases12,13

• failure to distinguish blood products in the aortic wall (in IMH) from atherosclerotic plaque21

Pitfalls • lack of clarity in the area of the aortic arch21

• false positive IMH in case of diffuse intramural atheromatosis20

MDCT

Advantages • very high (100%) sensitivity and specificity30,31

• requires less time than MRI• imaging of both the lumen and the aortic wall8• indication even for hemodynamically unstable patients31

• prediction of the progress of the aortic dissection31

• distinction of the false from the true lumen8,30,31

• excellent imaging of IMH when contrast agent is used, also providing information about its prognosis21,30

• reliable detection of displacement of intimal calcifications usually accompanying PAUDisadvantages • radiation toxicity27

• contrast medium toxicity27

• contrast medium is required for the investigation of the aortic wall21

• failure to investigate aortic valve and cardiac function12,23

• low sensitivity with regard to the aortic root21,47

• ECG-gated CT, which is appropriate for the investigation of the aortic root, involves higher radiation exposure for the patient21,24

• additional periaortic tissues, such as fat, lymphomas and tumors, may confuse the diagnosis21,43,50

Pitfalls • false positive diagnosis of aortic dissection in the case of: a) significant atheromatosis of the aortic wall,8 b) very dense signal of the aortic wall,19 c) reinforcement of the vibration of the wall of the ascending aorta19

• false negative picture of aortic dissection due to insufficient enhancement of the aortic wall• false positive picture of IMH in the area of the aortic root19,21,47 and in case of diffuse

atheromatosis,17,18,19 of inflammation of the aortic wall,17,18 or of periaortic diseases50

• false positive diagnosis of traumatic aortic injury in the case of remnant patent ductus arteriosus51



wall with translocation of intimal calcifications to-wards the lumen (Figure 7).18,25 Aortic wall thick-ness over 3 mm may be a sign of intramural hemato-ma.19,21 The density of this thickness is as high as 60-70 HU, similar to that of acute blood products.17,18,27 The feature that distinguishes between intramural hematoma and aortic dissection is the absence of the intimal flap and the intact intima of the aortic lu-men in the case of intramural hematoma. These da-ta, though, can be acquired only after contrast me-dium administration.19 An age over 70 years,21,32 lo-cation of the intramural hematoma in the ascending aorta,31,33 an aortic diameter over 45 mm34 or over 50 mm,35 aortic wall thickness over 10 mm,21,36 coexis-

tence with penetrating atherosclerotic ulcer,37 and the presence of pericardial or pleural effusion11 are some features of intramural hematoma that are related to a bad prognosis. Therefore, MDCT with contrast me-dium is an excellent diagnostic tool in the diagnosis of intramural hematoma, with sensitivity and speci-ficity ranging from 96%19 to 100%.17 Its disadvantage is its vagueness and artifacts with regard to the aortic root region, which can be avoided by using ECG-gat-ing CT—although this entails exposing the patient to a higher radiation dose.21

The method of choice in the diagnosis of pen-etrating atherosclerotic ulcer is contrast-enhanced CT (CECT), on which a penetrating atherosclerotic

MRI

Advantages • very high sensitivity and specificity:14 (95-98%) in the case of acute dissection41,42 and 95% in the case of IMH47

• without radiation burden8,20,21,27

• easy detection of both true and false lumen44

• potential avoidance of contrast medium administration8

• equally good detection of diseases of the aortic wall (IMH, PAU)14,18,20,21

• distinction of IMH from the atheromatous aortic wall33

• simultaneous investigation of cardiac function, aortic valve insufficiency and diseases of the pericardium19

• gold standard for operated and non-operated patients’ follow up40

• gadolinium used as contrast agent is less toxic than the iodinated contrast agents used in CT8,19,46

Disadvantages • cannot be performed in the emergency room27

• patient’s intolerance8,27

• deficient monitoring14,27

• contraindication when a pacemaker or a stent is present or after recent surgery48

• contraindication in hemodynamically unstable patients14

• more time-consuming than CT (15-20 min)14,21,40

• difficult differential diagnosis between IMH and other diseases of the aortic wall, such as atheromatosis, tumors, inflammation17,44

• lack of clarity with regard to the wall of the aortic root unless ECG-gated MRA is performed• gadolinium use does not provide an equally good picture of the aortic wall compared to that of

the aortic lumen21

• surgeons are less familiar with MRI evaluation• does not detect displacement of intimal calcifications19

Pitfalls • lack of clarity in cases of aortic wall thickening (atheromatosis, intramural thrombus, hematoma, tumors, aortitis, infiltration of the aorta by a mass derived out of the aorta)17,18

Aortography

Advantages • 88% sensitivity and 94% specificity in the diagnosis of acute aortic dissection8

• excellent imaging of the pathology of the lumen (AD, PAU)12,27

Disadvantages • radiation toxic to the patient and to the operator; more radiation than any other imaging method27

• contrast medium toxicity27

• time-consuming8

• cannot diagnose IMH or an atherosclerotic plaque of the aortic wall6,12,27

• invasiveness and requirement for an interventionist and a hemodynamic laboratory14,27

Pitfalls • false negative in the diagnosis of acute AD if the false lumen is thrombosed2,12,23

• false negative when the intimal flap is not detected8,23

• possibly false negative in the diagnosis of PAU unless there is adequate visibility13

AAS – acute aortic syndrome; IMH – intramural hematoma; PAU – penetrating atherosclerotic ulcer; TEE – transesophageal echocardiography; MDCT – multi-detector CT; MRI – magnetic resonance imaging.



ulcer appears as a “crater”—an interruption located at the smooth edge of the aortic wall—or as a pouch protruding out of the lumen.8,38 Penetrating athero-sclerotic ulcer often coexists with atheromatosis of the aortic wall around the ulcer, or more rarely with intramural hematoma.18,38 In addition, penetrating atherosclerotic ulcer may also coexist with local dis-section produced by the penetrating atherosclerotic ulcer itself (Figure 8). However, a penetrating athero-sclerotic ulcer may not be noticed even by CT.39

Finally, the disadvantages of CT (Table 1) are the following: a) toxic impact of the contrast medium on the kidneys;27 b) failure to evaluate any concomitant cardiac dysfunction or aortic valve insufficiency;12,23 c) significant “pitfalls’’ in case of its wrong perfor-mance or wrong interpretation.19

Magnetic resonance imaging

MRI is a safe, noninvasive and dynamic imaging di-agnostic tool that is able to visualize the structure of

Figure 3. Transesophageal echocardiography. Doppler flow imag-ing of the descending aorta. The flow in the true lumen (red color, towards transducer) presents with a huge characteristic “dicrotic notch” due to aortic insufficiency. A diastolic reverse flow during the entire diastolic period is also revealed and represents backflow due to severe aortic insufficiency

Figure 4. CT image. Acute dissection of the ascending aorta in a 73-year-old patient. The localized dissection (arrows) as well as the peri-cardial effusion can be seen.



the aorta with high resolution, while simultaneously providing information about cardiac function that is not provided by MDCT.8 Indeed, its many options, such as ECG-triggered spin-echo images, cine-MRI, contrast-enhanced techniques, gradient echo tech-niques, and gadolinium-enhanced three-dimensional MR angiography (MRA) techniques, allow us to ob-tain a perfect picture of the wall of the thoracic aorta, as well as information about aortic valve insufficiency, and the ejection fraction and the dimensions of the left ventricle.8,40

In the case of acute aortic dissection, MRI is an optimal and extremely reliable tool in the imaging of the intimal flap, the true and the false lumen, and possible thrombus. Thus, MRI has a sensitivity and specificity in the diagnosis of acute aortic dissection ranging from 95% to 100%.8,41,42 Based on the afore-mentioned features, MRI has 85% sensitivity and

100% specificity in the location of the site of entry, while it reaches 100% sensitivity and specificity in the identification of thrombus and of pericardial effusion due to rupture of the pericardium.8 Moreover, gado-linium-enhanced three-dimensional MRA techniques permit the rapid imaging of the thoracic and abdomi-nal aorta with their branches. In addition, contrast-enhanced MRA, performed with contrast medium administration, is able to detect the intimal flap and the extension of dissection to the arch vessels.8

In MRI, intramural hematoma typically appears as local thickening of the aortic wall, though with less di-agnostic clarity compared to the corresponding MDCT picture. A number of other diseases, such as athero-mas, tumors, mural thrombi, extravascular infiltra-tion of the aortic wall or its inflammatory thickening (aortitis), can mimic intramural hematoma (Table 1).20,21 The differential diagnosis is difficult, but may

Figure 5. CT image. Acute aortic dissection type A that includes the ascending aorta, the aortic arch and the descending aorta in a hyper-tensive 64-year-old man. The significantly dilated, less dense false lumen (blue arrow) can be seen, narrowing the true lumen (red arrow).



be helped by the form of the intima and lumen. Intra-luminal thrombus attached to the aortic wall occurs predominantly in the descending thoracic aorta and in a region of chronic aneurysm, which has a rough lumi-nal surface, while the luminal surface is intact when in-tramural hematoma appears.17,18 The acute aortic dis-section can rarely mimic intramural hematoma when the intimal flap is small, the vascular enhancement is insufficient and the communication between the true

and the false lumen is minor.21 A useful diagnostic sign on MRI is the fact that aortic dissection presents a spi-ral arrangement distally, whereas intramural hema-toma presents a crescent or circumferential arrange-ment.36,43 Finally, the typical MRI image of penetrat-ing atherosclerotic ulcer is a local crater roughly pro-truding into the aortic lumen.38,44-46

Generally, MRI has the following advantag-es (Table 1): a) it is associated with very high (95-

Figure 6. CT image. Type B dissection of the abdominal aorta. Fortunately, both the celiac artery (left circle) and the renal arteries (right circles) originate from the true lumen.

Figure 7. CT image. In the axial slice on the left, we can see an intramural hematoma of the descending aorta with its typical semilunar appearance (arrow) and intimal calcifications (circle). The sagittal slice on the right also shows an intramural hematoma (dotted arrow).



100%) sensitivity and specificity in the diagnosis of acute aortic dissection14,41,42 and intramural hemato-ma;47 b) it can identify the predominant flow through the true or the false lumen along the thoracic aorta and its branches;8 c) contrast medium is not always necessary;8 d) the patient suffers no radiation expo-sure;8,18,20,21 e) it detects aortic wall diseases, such as intramural hematoma and penetrating atheroscle-rotic ulcer, equally well;14 f) it is the imaging tool of choice for the follow up of patients operated for AAS;40 and g) the contrast agent used, gadolinium, is less toxic than the iodinated contrast agent adminis-tered for the performance of CT.8

However, there are also some disadvantages re-lated to MRI (Table 1): a) although it can be per-formed in 4-5 minutes,40 it usually requires 15-20 minutes;8,14,21 b) the patient experiences discomfort during the examination and adequate monitoring may not be applied;8,14,27 c) its performance may be ruled out or there may be ambiguity of the image in a patient who has a cardiac pacemaker, a mechanical

valve, a stent, a metallic implant, or recent surgery;48 d) it cannot be performed in hemodynamically un-stable patients;14 e) there are difficulties in the differ-ential diagnosis between intramural hematoma and other aortic wall diseases, such as the presence of an atherosclerotic plaque, a tumor, or inflammation of the wall;20,21 f) it suffers from ambiguity in the evalu-ation of the aortic root, although less than in the case of CT (ECG-gated MRA can be performed, although it requires more time, while the less toxic gadolinium contrast agent can be used);21 g) it cannot reveal dis-placement of the intimal calcifications of the aortic wall that usually accompany penetrating atheroscle-rotic ulcer;19 and h) surgeons are less familiar with evaluating the findings first hand and planning their surgical intervention. Indeed, according to IRAD, MRI is used as the first diagnostic examination in the diagnosis of AAS in just 2% of cases, whereas CT is used in 61%, ΤΕΕ or ΤΤΕ in 33%, and angiography in 4%.5,12 According to Rousseau et al,24 MRI consti-tutes an important alternative diagnostic tool in the

Figure 8. CT image. On the upper left, a penetrating atherosclerotic ulcer of the descending aorta with its accompa-nying hematoma (arrow) and escape of the contrast agent (circle) can be seen. The other axial slice on the left also represents a penetrating atherosclerotic ulcer with contrast agent escape (dotted arrow). A penetrating atheroscle-rotic ulcer of the descending aorta with a pseudoaneurysm is imaged on the right (dotted circle).



diagnosis of AAS in patients in whom MDCT angiog-raphy is contraindicated.

Aortography

Contrast aortography was the initial diagnostic tool used in the diagnosis of aortic dissection or traumatic rupture of the thoracic aorta. It was considered as the gold standard in the diagnosis of these diseases until the early 1990s.6 Nowadays, the other three diagnos-tic methods—CT, MR and TΕE—have replaced aor-tography in the diagnosis of AAS. Thus, the latter is performed in only 4% of cases.5,12,24 It is used in the context of arterial digital subtraction angiography, which can show the presence of intimal tear or a dou-ble lumen, difficulties in the perfusion of distal or-gans, stenosis of the coronary arteries, and potential concomitant aortic valve insufficiency.14

The disadvantages of aortography (Table 1) are the following: a) it outlines only the lumen of the aor-ta and does not provide any information about aortic wall pathology, such as in intramural hematoma;6,8,12 b) it may lead to false negative results because the inti-mal flap cannot be detected when the false lumen does not take contrast agent or when the true and the false lumen take contrast medium simultaneously;2,12,23 c) it may give a false negative result in the case of penetrat-ing atherosclerotic ulcer, when the visibility is not ade-quate;13 d) it requires more time for its performance;8 e) there is a risk of allergy or renal dysfunction due to contrast medium;12,23 f) the patient suffers more ra-diation exposure compared to the other imaging tech-niques;8 and g) it requires expert interventional cardi-ologists as operators and a hemodynamics laboratory.14

For the aforementioned reasons the sensitivity of

aortography is low, of the order of 88%, but its speci-ficity is 94%.8 Nowadays, we avoid using aortogra-phy because of the accompanying complications. As far as the diagnosis of AAS is concerned, aortogra-phy is used only in 20% of cases.8 Indeed, aortogra-phy is correlated with major complications, such as aortic dissection, rupture of the aorta or an aortic an-eurysm, embolic cerebrovascular episodes, and myo-cardial infarction in 5-6% of cases, and has a mortal-ity of 0.2%.49 However, it is used when the diagnosis has been established and a stent implantation is re-quired.12 In addition, aneurysms of the thoraco-ab-dominal aorta constitute an additional indication for the performance of aortography.14

Expert opinion

Acute aortic syndrome constitutes a series of diseas-es whose differential diagnosis is almost completely based on imaging. The chest X-ray can only provide information in the case of aortic rupture, acute aor-tic dissection, or traumatic rupture of the aorta. As far as acute aortic dissection is concerned, chest ra-diography can show abnormal data in only 60-90% of cases, having low sensitivity, about 64%, in the diagno-sis of AAS.3,6,7 TTE and TEE are cheap and safe di-agnostic methods that can be performed within 8-10 minutes and can be repeated without any burden to the patient. They can be performed in the emergency room or even by the patient’s bedside, but their find-ings are operator-dependent. Data concerning cardiac function can also be obtained. The sensitivity of TTE/TEE in the diagnosis of acute aortic dissection is high, reaching 88%, and it is the second most frequently used imaging diagnostic method (after CT), being ap-

Table 2. The differences between CT images of the two lumens (true and false) in cases of acute aortic dissection.1,8,19,48

Characteristic True lumen False lumen

Diameter Smaller BiggerDiameter during systole Increased DecreasedType of blood flow Laminar TurbulentVelocity of blood flow Rapid SlowPresence of thrombus No PossibleDensity of contrast More dense Less denseSpontaneous contrast No PresentExternal wall thickness Thicker ThinnerLocalization of the intimal flap Concave side Convex sideRelationship between the two lumens Surrounded Surrounding“Beak sign” Absent Possibly present“Cobweb sign” (net of connective tissue crossing the lumen) Absent Possibly present“Three lumen sign”, acute angle at the intersections between true and false lumen Proximal DistalConnection with the lumen of the normal aorta Direct connection (continuity) No connection



plied in 28-33% of cases, according to IRAD.2,12 The most popular imaging diagnostic method is CECT or MDCT39 which is used in 61% of cases of acute aortic dissection.5,12 It is accurate and provides information about both the aortic lumen and the aortic wall, but not cardiac function. Its sensitivity is over 93%.12 MRI constitutes the safest diagnostic method with regard to the patient, having great resolution in aortic diseases and a sensitivity of 95-100% in the diagnosis of acute aortic dissection14,41,42 and of 95% in the diagnosis of intramural hematoma.5,12 MRI simultaneously pro-vides data about cardiac function.8 Finally, aortogra-phy has the disadvantage of invasiveness, which is re-lated to various risks and difficulties of organization, thus being used in less than 5% of cases.6,8,12,14 How-ever, its sensitivity is relatively high, reaching 88% and its specificity is even higher (94%).8

In conclusion, the choice of the one or another of these imaging diagnostic tools depends on the doc-tors’ preferences in each hospital and does not have any remarkable effect on the final diagnosis of AAS.8

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Imaging of Acute Aortic Syndrome: Advantages ...€¦ · of acute aortic syndrome, so it is the first one performed. It can only shed light on some cases of AAS, concerning aortic