Guidelines and standards
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Surveillance imaging should be performed at intervals similar to what is recommended for aortic dissection. IV. THORACIC AORTIC ANEURYSM A. Definitions and Terminology Aortic aneurysm is a pathologic entity that is distinct from aortic dissection. The vast majority of aortic dissections (longitudinal splitting of the media) occur without preceding aneurysms. True an- eurysms result from stretching of the entire thickness of the aortic wall; thus, the wall of an aneurysm contains all three of its layers (intima, media, and adventitia). TAAs may involve one or more aortic segments (the aortic root, ascending aorta, arch, or descending thoracic aorta). Sixty percent of TAAs involve the aortic root and/or ascending tubular aorta, 40% involve the descending aorta, 10% involve the arch, and 10% involve the thoracoabdominal aorta. 243 In 1991, the joint councils of the Society of Vascular Surgery and the North American Chapter of the International Society for Cardiovascular Surgery appointed an ad hoc committee to define the standards for reporting on arterial aneurysm. 244
Aneurysm was defined as a permanent focal dilatation of an artery having a $50% increase in diameter compared with the expected normal diameter of the artery in question. This definition was also adopted by the 2010 American College of Cardiology Foundation, American Heart Association, American Association for Thoracic Surgery, American College of Radiology, American Surgical Association, Society for Cardiac Angiography and Interventions, Society of Interventional Radiology, Society of Thoracic Surgeons, and Society for Vascular Medicine guidelines for the diagnosis and man- agement of patients with thoracic aortic disease. 1 Figure 47 Diagram of some of the various shapes of aortic root and ascending aortic aneurysms. (A) Normal. (B) Characteristic ‘‘mar- fanoid’’ or ‘‘pear-shaped’’ aortic root with dilatation localized to the annulus and sinuses of Valsalva. (C, D) Two patterns of dilatation involving the annulus, sinuses of Valsalva, and ascending aorta. (E) Dilatation beginning at the STJ, but sparing the aortic annulus and sinuses of Valsalva. Table 16 Goal of imaging of TAAs 1 Confirm diagnosis 2 Measure maximal diameter of the aneurysm 3 Define longitudinal extent of the aneurysm 4 Measure the diameters of the proximal and distal margins of the aneurysm 5 Determine involvement of the aortic valve 6 Determine involvement of the arch vessel(s) 7 Detect periaortic hematoma or other sign of leakage 8 Differentiate from aortic dissection 9 Detect mural thrombus Journal of the American Society of Echocardiography Volume 28 Number 2 Goldstein et al 153
Although our writing committee endorses this definition in general, we would like to point out some practical considerations. First, the current definition lacks an outcomes correlate; second, many publications use the term aortic dilatation with different arbi- trary cutoff values to define the significance of dilatation. 245-248
Last, if a common echocardiographic upper limit of 37 mm is considered for the ascending aorta (see the section on normal anatomy and reference values), then the ascending aorta is dilated at a diameter of >55.5 mm (37 + 18.5 mm), which seems excessive given that it is larger than the typical threshold for surgery. General descriptions, such as ‘‘there is an ascending aortic aneurysm,’’ are inadequate. 243
It is preferable to state that ‘‘there is a 5-cm ascending thoracic aortic aneurysm,’’ because it conveys prognostic, follow-up, and management implications. Descriptive terms such as small, large, and giant to describe aneurysms should also be avoided. Other commonly used terms are included in the 2010 guidelines 1 :
Arteriomegaly is diffuse arterial dilatation involving several arterial segments, with an increase in diameter > 50% in comparison with the expected normal arterial diameter. Aortic dilatation is an acceptable nonspecific term that encom- passes both ectasia and aneurysm. Again, imaging reports must include the diameters of the affected aortic segments. Moreover, it is ideal to perform serial imaging studies at the same center with the same technique, so that direct comparisons can be made. 243
When this is not practical, direct comparison with previ- ous examinations should be made to confirm that serial changes are genuine. B. Classification of Aneurysms Aortic aneurysms can be classified according to morphology, location (as above), and etiology. The etiologies of TAAs are listed in Table 15 . These are discussed in other sections of this document. C. Morphology Aneurysms of the aorta can be classified into two morphologic types: fusiform and saccular ( Figure 46 ). Fusiform aneurysms, which are more common than saccular aneurysms, result from diffuse weak- ening of the aortic wall. This process leads to dilatation of the entire circumference of the aorta, producing a spindle-shaped deformity with a tapered beginning and end. Saccular aneurysms result when only a portion of the aortic circumference is weakened, producing an asymmetric, relatively focal balloon-shaped out-pouching. There are also various morphologic shapes of the aortic root and ascending aorta, some of which suggest specific etiologies ( Figure 47 ). The major goals of imaging TAAs are listed in Table 16 , and
recommendations for choice of imaging modalities are listed in Table 17
. D. Serial Follow-Up of Aortic Aneurysms (Choice of Tests) Aortic diameter is the principal predictor of aortic rupture or dissec- tion.
249 The risk for rupture or dissection of TAAs from different eti- ologies increases significantly at sizes > 60 mm. The mean rupture rate is only 2% per year for aneurysms <50 mm in diameter, rising slightly to 3% for aneurysms with diameters of 50 to 59 mm, but increasing sharply to 7% per year for aneurysms $60 mm in Table 17
Recommendations for choice of imaging modality for TAA Modality
Recommendation Advantages Disadvantages CT First-line First-line technique for staging, surveillance Contrast: enhanced CT and MRI very accurate for measuring size of all TAAs (superior to echocardi- ography for distal ascending aorta, arch, and de- scending aorta) All segments of aorta and aortic branches well visu- alized Use of ionizing radiation and ICM Cardiac motion can cause imaging artifacts MRI
Second-line Ideal technique for comparative follow-up studies Excellent modality in stable patients Preferred for follow-up for younger patients Avoids ionizing radiation Can image entire aorta Examination times longer than CT Benefits from patient cooperation (breath hold) Limited in emergency situations in unstable patients and patients with implantable metallic devices Benefits from gadolinium TTE
Second-line Usually diagnostic for aneurysms effecting aortic root Useful for family screening Useful for following aortic root disease Excellent reproducibility of measurements Excellent for AR, LV function Distal ascending aorta, arch, and descending aorta not reliably imaged TEE
Third-line Excellent for assessment of AR mechanisms Excellent images of aortic root, ascending aorta, arch, and descending thoracic aorta Less valuable for routine screening or serial follow- up (semi-invasive) Distal ascending aorta may be poorly imaged Does not permit full visualization of arch vessels Limited landmarks for serial examinations Aortography Third-line Reserved for therapeutic intervention Useful to guide endovascular procedures Invasive; risk for contrast-induced nephropathy Visualizes only aortic lumen Does not permit accurate measurements LV, Left ventricular. 154 Goldstein et al Journal of the American Society of Echocardiography February 2015 diameter. 250
The rate of growth is significantly greater for aneurysms of the descending aorta, at 1.9 mm per year, than those of the ascending aorta, at 0.07 mm per year. 249
The clinical importance of the maximum aortic diameter for deter- mining the timing of prophylactic surgical repair implies makes it critical that measurements be made as accurately as possible. It is essential for the same observer to compare measurements side by side using the same anatomic references. Tomographic scans in a situation for which the aorta does not lie perpendicular to the plane of the scan produce an elliptical image with major (maximum) and minor (minimum) diame- ters. Because the major diameter is typically an overestimate, in most natural history studies of aneurysm expansion, the minimum diameter has been reported to avoid the effect of obliquity. Aortic root dilatation can be followed by TTE in most cases. Diameter expansion, severity of AR, and left ventricular function may be accurately evaluated when the echocardiographic window is adequate. However, when dilatation involves the ascending aorta above the STJ, TTE does not always adequately visualize the affected segment, in which case CTor MRI should be performed. TEE may be warranted when the type of surgical treatment (repair or valve replacement) is being considered. Both TTE and TEE have limitations for adequate measurement of distal ascending aorta, aortic arch, and descending aorta diameters. In addition, if the aorta is tortuous, trans- esophageal echocardiographic images may be difficult to measure accurately. The multiplanar capacity of MDCT, together with its sub- millimeter spatial resolution, renders it an excellent technique for in- terval surveillance of both thoracic and abdominal aortic aneurysms. Measurements must adhere to a strict protocol that permits compar- ison between different imaging techniques as well as follow-up of the patient. MDCT permits one to choose an imaging plane in any arbi- trary space orientation; thus, it is possible to easily find the maximum aortic diameter plane, which must be perpendicular to the longitudi- nal plane of the aortic segment. When the axial data are reconstructed into 3D images (computed tomographic angiography), one can mea- sure the tortuous aorta in true cross-section and obtain an accurate diameter. Measurements should be taken on multiplane reconstruc- tion images. A further common presentation of data is a parasagittal, oblique MIP plane that passes through the aortic root, ascending aorta, aortic arch, and descending aorta. The MIP plane must have a thickness proportional to the aortic tortuosity to make sure that the maximum diameter is included in the image. This plane is easily reproducible and comparable in follow-up studies. MRI accurately defines aortic diameter, aneurysm extent, and the aneurysm’s relationship with the main arterial branches. It is recom- mended to combine MR angiographic images with black-blood spin- echo sequences, which are useful for detecting pathology of the wall and adjacent structures that could go unnoticed if only MR angio- graphic images are acquired. In mycotic aneurysm, postcontrast T1- weighted images permit the identification of inflammatory changes in the aortic wall and adjacent fat, secondary to bacterial infection. The in- formation provided by MRA in aortic aneurysm assessment is similar to that offered by current MDCT. Both methods permit accurate determi- nations of aortic diameters in sagittal plane. Furthermore, postprocess- ing techniques (MIP, multiplane reconstruction, and volume rendering) facilitate visualization of the aorta in its entirety, together with the rela- tionship of its principal branches, and are highly useful when planning treatment. The sagittal plane makes it possible to obtain more repro- ducible measurements. In asymptomatic patients with aortic aneu- rysms and those approaching the need for surgery, imaging techniques should be performed at 6-month intervals until aortic size remains stable, in which case imaging may be annual. 1. Algorithm for Follow-Up. TTE can be used for serial imaging of the dilated aortic root and proximal ascending aorta when agreement between the dimensions measured by TTE and CT or MRI has been established. When the aneurysm is located in the mid or upper portion of the ascending aorta, aortic arch, or descending thoracic aorta, CT or MRI is recommended for follow-up. Measurements should be made on multiplane reconstruction images or in parasagit- tal, oblique MIP plane that passes through the involved aortic segments. Although annual surveillance MDCT has been recommen- ded, the strategy is not well established and should be individualized from annually to every 2 to 3 years depending on the abnormalities present, history of complications among family members, the present size, and the degree of change in size over time. E. Use of TEE to Guide Surgery for TAAs When patients with aortic root or ascending TAAs undergo aortic repair, the anatomy of the aorta and aortic valve has usually been defined preoperatively. Nevertheless, it is always wise to use intrao- perative TEE to confirm the prior imaging findings. The initial intrao- perative transesophageal echocardiographic examination should begin before the initiation of cardiopulmonary bypass, so the physi- ology of the aortic valve can be assessed. If the valve is bicuspid, one should determine the presence and severity of associated valvular aortic stenosis, regurgitation, or both. If there is significant AR, one should determine the mechanism, looking specifically for prolapse and/or retraction of the conjoined leaflet, as this is a common cause of bicuspid AR and may be correctable with BAV repair. One should also assess the degree of leaflet thickening, calcification, and restric- tion, because in the setting of significant valve dysfunction, these find- ings may influence the surgeon’s decision regarding the need for valve repair or replacement. Even when the aortic valve is tricuspid with otherwise normal leaf- lets, the presence of an ascending aortic aneurysm can result in AR. The commissures of the aortic leaflets are located just below the STJ; dilatation of the aorta at that level may tether the leaflets, leaving insufficient slack for the three leaflets to coapt properly in the middle, resulting in a jet of central AR. 32,194,251 AR due to leaflet tethering can occur with aneurysms of both the aortic root and the ascending aorta. Fortunately, with repair of the aneurysm and restoration of normal aortic geometry, normal leaflet coaptation is often restored, which in turn leads to resolution of the valvular regurgitation. Therefore, in a patient with an aneurysm with significant AR, identifying such aortic leaflet tethering on preoperative TEE may reassure the surgeon that aortic valve replacement is not necessary. The ascending aorta, aortic arch, and descending aorta should each be inspected for the presence of associated pathology, such as an unrec- ognized aortic dissection, IMH, PAU, or protruding atheromas. Large atheromas in the ascending aorta or arch may prompt additional imag- ing of the aorta using intraoperative epiaortic echocardiography and in- fluence decisions regarding the site of aortic cannulation and perfusion. Postoperative TEE should begin as soon as the patient comes off cardiopulmonary bypass. The examination should begin with inspec- tion of the aortic valve, as unanticipated valve dysfunction may neces- sitate a return to bypass. If preoperatively there had been significant AR due to leaflet tethering, one should confirm appropriate leaflet coaptation and alleviation of AR after repair. If repair of bicuspid valve prolapse was performed, one should confirm that the prolapse has resolved and that the AR is no longer significant. If a valve-sparing root repair was performed, one should confirm that the three aortic valve leaflets coapt normally and that there is little or no AR. If the Journal of the American Society of Echocardiography Volume 28 Number 2 Goldstein et al 155
aortic valve had been replaced, one should confirm that the prosthetic leaflet or disk motion is normal, that there is no more than physiologic AR, and that there are no paravalvular leaks. After aortic valve replacement or aortic root replacement, it is typical to see focal thickening around the aortic root. It is important to docu- ment this so as not to confuse this finding with pathology on subsequent imaging. For more detailed information, readers are referred to the recently published Society of Thoracic Surgeons aortic valve and ascending aorta guidelines for management and quality measures. 252
F. Specific Conditions 1. Marfan Syndrome. Marfan syndrome is an inherited disorder of connective tissue that occurs as a result of a mutation in the FBN1 gene, which encodes fibrillin. One of the hallmark features of this dis- order is dilatation or dissection of the proximal ascending aorta (aortic root). 253
The remaining portions of the aorta may also dilate and dissect, but involvement of the aortic root is expected when there is associated vascular disease. Noninvasive aortic imaging with subse- quent elective aortic replacement has contributed to the dramatic improvement in survival noted in patients with Marfan syndrome over the past few decades. 254
tion and serial follow-up of ascending aortic enlargement in patients with known or suspected Marfan syndrome, because of its availability, noninvasive nature, reliability, and lack of need for radiation or contrast material. Characteristic aortic features include dilatation of the aortic root, whereas the STJ and remaining portions of the ascending aorta generally are normal in size ( Figure 48 ). Normative values are used to determine the presence and extent of aortic enlargement on the ba- sis of age and BSA. 9 The leading edge–to–leading edge measurement technique is generally performed in patients with Marfan syndrome <18 years of age, and the size of the aorta is reported along with the Z score.
255 Although there is dispute regarding the best echocardio- graphic aortic measurement method, the most important concept is that serial measurements for each individual patient are performed us- ing the same method to determine aortic dimension change over time. Some patients with Marfan syndrome have suboptimal transthoracic echocardiographic images, and in these patients, serial CT or MRI is required to monitor aortic diameter. At the time of initial diagnosis of aortopathy in Marfan syndrome by TTE, additional imaging with CT or MRI is generally recommen- ded to confirm that the size of the aorta measured by TTE is accurate and correlates with the computed tomographic or MRI measurement and to document the diameters of the distal ascending aorta, aortic arch, and descending aortic segments, which may also be enlarged but are often incompletely visualized by TTE ( Figure 49 ). For the follow-up of aortic root enlargement in patients with Marfan syndrome, follow-up imaging in 6 months is recommended. If at that time the aortic diameter remains stable, is <45 mm, and there is no family or personal history of aortic dissection, then annual aortic imaging is reasonable. Patients with Marfan syndrome who do not meet these criteria should undergo repeat aortic imaging every 6 months.
TTE can be used for serial imaging follow-up of the dilated ascending aorta when correlation between the dimensions measured by TTE and CT or MRI has been documented. Occasionally, patients with Marfan syndrome do not demonstrate aortic enlargement until well into adulthood. These patients can be referred for transthoracic echocardiographic screening at 2- to 3-year intervals. Repeat CT or MRI is suggested at least every 3 years in patients with Marfan syndrome to reassess the aortic arch and descending Figure 48
long-axis image
demonstrating marked dilatation of the aortic root (sinuses) in a patient with Marfan syndrome. Note the normal dimension at the STJ. Figure 49 Computed tomographic 3D volume-rendered recon- struction of the thoracic aorta demonstrating aortic root dilata- tion (arrow) and proximal descending thoracic aorta dilatation (asterisk). The descending thoracic aortic dilatation was not noted on TTE. 156 Goldstein et al Journal of the American Society of Echocardiography February 2015 aorta and to reconfirm that TTE remains reliable in its measurement of the ascending aorta. Patients with Marfan syndrome with aneu- rysmal dilatation of the proximal descending thoracic aorta require regular CT or MRI to monitor aortic stability, because TTE does not provide reliable imaging of this region. TEE is generally not used for the initial diagnosis or follow-up of aortic dilatation in patients with Marfan syndrome because of its Yüklə 9,02 Mb. Dostları ilə paylaş:
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