HomeCirculationVol. 121, No. 132010 ACCF/AHA/AATS/ACR/ASA/SCA/SCAI/SIR/STS/SVM Guidelines for the Diagnosis and Management of Patients With Thoracic Aortic Disease: Executive Summary Free AccessReview ArticlePDF/EPUBAboutView PDFView EPUBSections ToolsAdd to favoritesDownload citationsTrack citationsPermissionsDownload Articles + Supplements ShareShare onFacebookTwitterLinked InMendeleyReddit Jump toSupplementary MaterialsFree AccessReview ArticlePDF/EPUB2010 ACCF/AHA/AATS/ACR/ASA/SCA/SCAI/SIR/STS/SVM Guidelines for the Diagnosis and Management of Patients With Thoracic Aortic Disease: Executive SummaryA Report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines, American Association for Thoracic Surgery, American College of Radiology, American Stroke Association, Society of Cardiovascular Anesthesiologists, Society for Cardiovascular Angiography and Interventions, Society of Interventional Radiology, Society of Thoracic Surgeons, and Society for Vascular Medicine WRITING COMMITTEE MEMBERS Loren F. Hiratzka, MD, Chair, George L. Bakris, MD, Joshua A. Beckman, MD, MS, Robert M. Bersin, MPH, MD, Vincent F. Carr, DO, Donald E. CaseyJr, MD, MPH, MBA, Kim A. Eagle, MD, Luke K. Hermann, MD, Eric M. Isselbacher, MD, Ella A. Kazerooni, MD, MS, Nicholas T. Kouchoukos, MD, Bruce W. Lytle, MD, Dianna M. Milewicz, MD, PhD, David L. Reich, MD, Souvik Sen, MD, MS, Julie A. Shinn, RN, MA, CCRN, Lars G. Svensson, MD, PhD and David M. Williams, MD WRITING COMMITTEE MEMBERS , Loren F. HiratzkaLoren F. Hiratzka , George L. BakrisGeorge L. Bakris , Joshua A. BeckmanJoshua A. Beckman , Robert M. BersinRobert M. Bersin , Vincent F. CarrVincent F. Carr , Donald E. CaseyJrDonald E. CaseyJr , Kim A. EagleKim A. Eagle , Luke K. HermannLuke K. Hermann , Eric M. IsselbacherEric M. Isselbacher , Ella A. KazerooniElla A. Kazerooni , Nicholas T. KouchoukosNicholas T. Kouchoukos , Bruce W. LytleBruce W. Lytle , Dianna M. MilewiczDianna M. Milewicz , David L. ReichDavid L. Reich , Souvik SenSouvik Sen , Julie A. ShinnJulie A. Shinn , Lars G. SvenssonLars G. Svensson and David M. WilliamsDavid M. Williams Originally published16 Mar 2010https://doi.org/10.1161/CIR.0b013e3181d47d48Circulation. 2010;121:1544–1579is corrected byCorrectionCorrectionOther version(s) of this articleYou are viewing the most recent version of this article. Previous versions: March 16, 2010: Previous Version 1 Table of ContentsPreamble …15451. Introduction …1546 1.1. Methodology and Evidence Review …1546 1.2. Organization of the Writing Committee …1548 1.3. Document Review and Approval …1548 1.4. Scope of the Guideline …1548 1.4.1. Critical Issues …1548 1.5. Glossary of Terms and Abbreviations Used Throughout the Guideline …15492. The Thoracic Aorta …15493. Thoracic Aortic Histopathology …1549 3.1. Atherosclerosis …1549 3.2. Aneurysms and Dissections …1549 3.3. Vasculitis and Inflammatory Diseases …15504. Recommendations for Aortic Imaging Techniques to Determine the Presence and Progression of Thoracic Aortic Disease …1550 4.1. Chest X-Ray …1552 4.2. Computed Tomographic Imaging …1552 4.3. Magnetic Resonance Imaging …1552 4.4. Echocardiography …15525. Recommendations for Genetic Syndromes …15536. Recommendations for Familial Thoracic Aortic Aneurysm and Dissections …15547. Recommendations for Bicuspid Aortic Valve and Associated Congenital Variants in Adults …15558. Recommendations for Takayasu Arteritis and Giant Cell Arteritis …15559. Recommendations for Estimation of Pretest Risk of Thoracic Aortic Dissection …155610. Initial Evaluation and Management of Acute Thoracic Aortic Disease …1557 10.1. Recommendations for Screening Tests …1557 10.2. Recommendations for Diagnostic Imaging Studies …1559 10.3. Recommendations for Initial Management …1559 10.4. Recommendations for Definitive Management …156011. Recommendation for Surgical Intervention for Acute Thoracic Aortic Dissection …156012. Recommendation for Intramural Hematoma Without Intimal Defect …156013. Recommendation for History and Physical Examination for Thoracic Aortic Disease …156014. Recommendation for Medical Treatment of Patients With Thoracic Aortic Diseases …1560 14.1. Recommendations for Blood Pressure Control …1561 14.2. Recommendation for Dyslipidemia …1562 14.3. Recommendation for Smoking Cessation …156215. Recommendations for Asymptomatic Patients With Ascending Aortic Aneurysm …156316. Recommendation for Symptomatic Patients With thoracic Aortic Aneurysm …156417. Recommendations for Open Surgery for Ascending Aortic Aneurysm …156418. Recommendations for Aortic Arch Aneurysms …156519. Recommendations for Descending Thoracic Aorta and Thoracoabdominal Aortic Aneurysms …156620. Recommendations for Counseling and Management of Chronic Aortic Diseases in Pregnancy …156621. Recommendations for Aortic Arch and Thoracic Aortic Atheroma and Atheroembolic Disease …156722. Periprocedural and Perioperative Management …1567 22.1. Recommendations for Preoperative Evaluation …1567 22.2. Recommendations for Choice of Anesthetic and Monitoring Techniques …1567 22.3. Recommendation for Transfusion Management and Anticoagulation in Thoracic Aortic Surgery …1568 22.4. Recommendations for Brain Protection During Ascending Aortic and Transverse Aortic Arch Surgery …1568 22.5. Recommendations for Spinal Cord Protection During Descending Aortic Open Surgical and Endovascular Repairs …1568 22.6. Recommendations for Renal Protection During Descending Aortic Open Surgical and Endovascular Repairs …156823. Recommendations for Surveillance of Thoracic Aortic Disease or Previously Repaired Patients …156924. Recommendation for Employment and Lifestyle in Patients With Thoracic Aortic Disease …156925. Tumors of the Thoracic Aorta …156926. Recommendations for Quality Assessment and Improvement for Thoracic Aortic Disease …1570Appendix 1. Author Relationships With Industry and Other Entities …1571Appendix 2. Reviewer Relationships With Industry and Other Entities …1573References …1574PreambleIt is essential that the medical profession play a central role in critically evaluating the evidence related to drugs, devices, and procedures for the detection, management, or prevention of disease. Properly applied, rigorous, expert analysis of the available data documenting absolute and relative benefits and risks of these therapies and procedures can improve outcomes and reduce costs of care by focusing resources on the most effective strategies. One important use of such data is the production of clinical practice guidelines which, in turn, can provide a foundation for a variety of other applications such as performance measures, appropriate use criteria, clinical decision support tools, and quality improvement tools.The American College of Cardiology Foundation (ACCF) and the American Heart Association (AHA) have jointly engaged in the production of guidelines in the area of cardiovascular disease since 1980. The ACCF/AHA Task Force on Practice Guidelines is charged with developing, updating, and revising practice guidelines for cardiovascular diseases and procedures, and the Task Force directs and oversees this effort. Writing committees are charged with assessing the evidence as an independent group of authors to develop, update, or revise recommendations for clinical practice.Experts in the subject under consideration have been selected from both organizations to examine subject-specific data and write guidelines in partnership with representatives from other medical practitioner and specialty groups. Writing committees are specifically charged to perform a formal literature review, weigh the strength of evidence for or against particular treatments or procedures, and include estimates of expected health outcomes where data exist. Patient-specific modifiers, comorbidities, and issues of patient preference that may influence the choice of tests or therapies are considered. When available, information from studies on cost is considered, but data on efficacy and clinical outcomes constitute the primary basis for recommendations in these guidelines.The ACCF/AHA Task Force on Practice Guidelines makes every effort to avoid actual, potential, or perceived conflicts of interest that may arise as a result of industry relationships or personal interests among the writing committee. Specifically, all members of the writing committee, as well as peer reviewers of the document, are asked to disclose all current relationships and those 24 months prior to initiation of the writing effort that may be perceived as relevant. All guideline recommendations require a confidential vote by the writing committee and must be approved by a consensus of the members voting. Members who were recused from voting are noted on the title page of this document. Members must recuse themselves from voting on any recommendation where their relationships with industry (RWI) and other entities apply. If a writing committee member develops a new relationship with industry during his/her tenure, he/she is required to notify guideline staff in writing. These statements are reviewed by the Task Force on Practice Guidelines and all members during each conference call and/or meeting of the writing committee, updated as changes occur, and ultimately published as an appendix to the document. For detailed information regarding guideline policies and procedures, please refer to the methodology manual for ACCF/AHA Guideline Writing Committees.1 RWI and other entities pertinent to this guideline for authors and peer reviewers are disclosed in Appendixes 1 and 2, respectively. Disclosure information for the ACCF/AHA Task Force on Practice Guidelines is also available online at http://www.acc.org/about/overview/ClinicalDocumentsTaskForces.cfm.These practice guidelines are intended to assist healthcare providers in clinical decision making by describing a range of generally acceptable approaches for diagnosis, management, and prevention of specific diseases or conditions. Clinicians should consider the quality and availability of expertise in the area where care is provided. These guidelines attempt to define practices that meet the needs of most patients in most circumstances. The recommendations reflect a consensus after a thorough review of the available current scientific evidence and are intended to improve patient care. The Task Force recognizes that situations arise where additional data are needed to better inform patient care; these areas will be identified within each respective guideline when appropriate.Patient adherence to prescribed and agreed upon medical regimens and lifestyles is an important aspect of treatment. Prescribed courses of treatment in accordance with these recommendations are effective only if they are followed. Because lack of patient understanding and adherence may adversely affect outcomes, physicians and other healthcare providers should make every effort to engage the patient's active participation in prescribed medical regimens and lifestyles.If these guidelines are used as the basis for regulatory or payer decisions, the goal should be improvement in quality of care and aligned with the patient's best interest. The ultimate judgment regarding care of a particular patient must be made by the healthcare provider and the patient in light of all of the circumstances presented by that patient. Consequently, there are circumstances in which deviations from these guidelines are appropriate.The guidelines will be reviewed annually by the ACCF/AHA Task Force on Practice Guidelines and considered current unless they are updated, revised, or withdrawn from distribution. The full-text guidelines are e-published in the April 6, 2010, issues of the Journal of the American College of Cardiology and Circulation.1aAlice K. Jacobs, MD, FACC, FAHAChair, ACCF/AHA Task Force on Practice GuidelinesSidney C. Smith, Jr, MD, FACC, FAHAImmediate Past Chair, ACCF/AHA Task Force on Practice Guidelines1. Introduction1.1. Methodology and Evidence ReviewThe writing committee conducted a comprehensive search of the medical and scientific literature through the use of PubMed/MEDLINE. Searches were limited to publications written in the English language. Compiled reports were reviewed and additional articles were provided by committee members. Specifically targeted searches were conducted on the following subtopics: acute aortic dissection, ankylosing spondylitis, aortic dissection and litigation, aortic neoplasm, aortic tumors, Behçet disease, bicuspid aortic valve, calcified aorta, chronic dissection, coarctation of the aorta, D-dimer, dissecting aneurysm, Ehlers-Danlos syndrome, endovascular and aortic aneurysms, medial degeneration, porcelain aorta, giant cell arteritis, imaging and thoracic aortic disease, inflammatory disease, intramural hematoma, Loeys-Dietz syndrome, Marfan syndrome, Noonan syndrome, penetrating aortic ulcer, polycystic kidney disease, thoracic and aortic aneurysms, thoracic aortic disease and patient care, thoracic aortic disease and surgery, thoracic aorta and Kawasaki disease, Takayasu arteritis, thoracoabdominal and aorta or aortic disease, and Turner syndrome. More than 850 references were reviewed, with 830 used as the primary evidence base for the final guideline. The ACCF/AHA Task Force on Practice Guidelines methodology processes were followed to write the text and recommendations. In general, published manuscripts appearing in journals listed in Index Medicus were used as the evidence base. Published abstracts were used only for emerging information but were not used in the formulation of recommendations.The committee reviewed and ranked evidence supporting current recommendations with the weight of evidence ranked as Level A if the data were derived from multiple randomized clinical trials or meta-analyses. The committee ranked available evidence as Level B when data were derived from a single randomized trial or nonrandomized studies. Evidence was ranked as Level C when the primary source of the recommendation was consensus opinion, case studies, or standard of care. In the narrative portions of these guidelines, evidence is generally presented in chronologic order of development. Studies are identified as observational, retrospective, prospective, or randomized. For certain conditions for which inadequate data are available, recommendations are based on expert consensus and clinical experience and are ranked as Level C. An analogous example is the use of penicillin for pneumococcal pneumonia, where there are no randomized trials and treatment is based on clinical experience. When recommendations at Level C are supported by historical clinical data, appropriate references (including clinical reviews) are cited if available. For issues where sparse data are available, a survey of current practice among the clinicians on the writing committee formed the basis for Level C recommendations and no references are cited. The schema for classification of recommendations and level of evidence is summarized in Table 1, which also illustrates how the grading system provides an estimate of the size of the treatment effect and an estimate of the certainty of the treatment effect. Download figureDownload PowerPointTable 1. Applying Classification of Recommendations and Level of Evidence*Data available from clinical trials or registries about the usefulness/efficacy in different subpopulations, such as sex, age, history of diabetes, history of prior myocardial infarction, history of heart failure, and prior aspirin use. A recommendation with Level of Evidence B or C does not imply that the recommendation is weak. Many important clinical questions addressed in the guidelines do not lend themselves to clinical trials. Even though randomized trials are not available, there may be a very clear clinical consensus that a particular test or therapy is useful or effective.†In 2003, the ACCF/AHA Task Force on Practice Guidelines developed a list of suggested phrases to use when writing recommendations. All guideline recommendations have been written in full sentences that express a complete thought, such that a recommendation, even if separated and presented apart from the rest of the document (including headings above sets of recommendations), would still convey the full intent of the recommendation. It is hoped that this will increase readers' comprehension of the guidelines and will allow queries at the individual recommendation level.To provide clinicians with a comprehensive set of data, whenever possible, the exact event rates in various treatment arms of clinical trials are presented to permit calculation of the absolute risk difference (ARD), number needed to harm (NNH); the relative treatment effects are described either as odds ratio (OR), relative risk (RR), or hazard ratio (HR) depending on the format in the original publication. Along with all other point statistics, confidence intervals (CIs) for those statistics are added when available.The writing committee recognized that the evidence base for this guideline is less robust in terms of randomized clinical trials than prior ACCF/AHA guidelines, particularly those focused on coronary artery disease (CAD) and heart failure. As the reader will discern, much of the evidence base for this topic consists of cohort studies and retrospective reviews, which largely emanate from centers with a specialized interest in specific types of thoracic aortic disease. The writing committee attempted to focus on providing the practitioner with recommendations for evaluation and treatment wherever possible and where controversy exists, identified as such in the text.The writing committee acknowledges the expertise of the highly experienced and effective practice guidelines staff of the ACCF and AHA. The writing committee chair also acknowledges the commitment and dedication of the diverse writing committee members who were able to put aside issues of specialty "turf" and focus on providing the medical community with a guideline aimed at optimal patient care.1.2. Organization of the Writing CommitteeThe guideline was written by a committee comprised of experts in cardiovascular medicine, surgery, radiology, and nursing. For many of the previous ACCF/AHA practice guidelines, writing expertise has been available within these 2 organizations. Because of the broad scope and diversity of thoracic aortic diseases, as well as the specialists who treat such patients, the ACCF and AHA sought greater involvement from many specialty organizations. Most, but not all, specialty organizations that represent the major stakeholders caring for patients with thoracic aortic diseases provided writing committee members and financial support of the project, and they are recognized as marquee level partners with the ACCF and AHA. These organizations included the American Association for Thoracic Surgery (AATS), American College of Radiology (ACR), American Stroke Association (ASA), Society of Cardiovascular Anesthesiologists (SCA), Society for Cardiovascular Angiography and Interventions (SCAI), Society of Interventional Radiology (SIR), Society of Thoracic Surgeons (STS), and Society for Vascular Medicine (SVM). The American College of Emergency Physicians (ACEP) and the American College of Physicians (ACP) were also represented on the writing committee. Where additional expertise was needed, the scientific councils of the AHA were contacted for writing committee representatives. Representation was provided or facilitated by the Councils on Cardiovascular Nursing, Cardiovascular Surgery and Anesthesia, Cardiovascular Radiology and Intervention, and Clinical Cardiology, Council for High Blood Pressure Research, and Stroke Council.1.3. Document Review and ApprovalThis document was reviewed by 3 outside reviewers nominated by the ACCF and 2 outside reviewers nominated by the AHA, as well as 1 or 2 reviewers from each of the following organizations: the AATS, ACP, ACEP, ACR, ASA, SCA, SCAI, SIR, STS, and the SVM. It was also reviewed by 6 individual content reviewers—2 content reviewers from the ACCF Catheterization Committee and 1 content reviewer from the ACCF Interventional Council. All reviewer RWI information was collected and distributed to the writing committee and is published in this document (see Appendix 2).This document was approved for publication by the governing bodies of the ACCF and the AHA; and the AATS, ACEP, ACR, ASA, SCA, SCAI, SIR, STS, and SVM and was endorsed by the North American Society for Cardiovascular Imaging.1.4. Scope of the GuidelineThe term thoracic aortic disease encompasses a broad range of degenerative, structural, acquired, genetic-based, and traumatic disease states and presentations. According to the Centers for Disease Control and Prevention death certificate data, diseases of the aorta and its branches account for 43 000 to 47 000 deaths annually in the United States.2 The precise number of deaths attributable to thoracic aortic diseases is unclear. However, autopsy studies suggest that the presentation of thoracic aortic disease is often death due to aortic dissection (AoD) and rupture, and these deaths account for twice as many deaths as attributed to ruptured abdominal aortic aneurysms (AAAs).3 The diagnosis of acute thoracic AoD or rupture is often difficult and delayed, and errors in diagnosis may account for deaths otherwise attributed to cardiac arrhythmia, myocardial infarction (MI), pulmonary embolism, or mesenteric ischemia.Most patients with significant thoracic aortic disease will be directed to specialized practitioners and institutions. However, the importance of early recognition and prompt treatment and/or referral for a variety of thoracic aortic diseases by all healthcare professionals provides the rationale for this document. This guideline will provide the practitioner with a sufficient description of background information, diagnostic modalities, and treatment strategies so that appropriate care of these patients can be facilitated and better understood. The goal of this guideline is to improve the health outcomes and quality of life for all patients with thoracic aortic disease.This guideline includes diseases involving any or all parts of the thoracic aorta with the exception of aortic valve diseases4 and includes the abdominal aorta when contiguous thoracic aortic diseases are present. Specific disease states are described in the following sections and the reader is referred to the glossary of terminology in Section 1.5 for abbreviations used throughout the guideline.1.4.1. Critical IssuesAs the writing committee developed this guideline, several critical issues emerged: Thoracic aortic diseases are usually asymptomatic and not easily detectable until an acute and often catastrophic complication occurs. Imaging of the thoracic aorta with computed tomographic imaging (CT), magnetic resonance imaging (MR), or in some cases, echocardiographic examination is the only method to detect thoracic aortic diseases and determine risk for future complications.Radiologic imaging technologies have improved in terms of accuracy of detection of thoracic aortic disease. However, as the use of these technologies has increased, so also has the potential risk associated with repeated radiation exposure, as well as contrast medium–related toxicity. Whether these technologies should be used repeatedly as a widespread screening tool is discussed in the full-text document. In addition, the writing committee formulated recommendations on a standard reporting format for thoracic aortic findings as discussed in Section 4.Imaging for asymptomatic patients at high risk based on history or associated diseases is expensive and not always covered by payers.For many thoracic aortic diseases, results of treatment for stable, often asymptomatic, but high-risk conditions are far better than the results of treatment required for acute and often catastrophic disease presentations. Thus, the identification and treatment of patients at risk for acute and catastrophic disease presentations (eg, thoracic AoD and thoracic aneurysm rupture) prior to such an occurrence are paramount to eliminating the high morbidity and mortality associated with acute presentations.A subset of patients with acute AoD are subject to missed or delayed detection of this catastrophic disease state. Many present with atypical symptoms and findings, making diagnosis even more difficult. This issue has come under greater medical-legal scrutiny, and specific cases have been widely discussed in the public domain. Widespread awareness of the varied and complex nature of thoracic aortic disease presentations has been lacking, especially for acute AoD. Risk factors and clinical presentation clues are noted in Section 9. The collaboration and cosponsorship of multiple medical specialties in the writing of this guideline will provide unique opportunities for widespread dissemination of knowledge to raise the level of awareness among all medical specialties.There is rapidly accumulating evidence that genetic alterations or mutations predispose some individuals to aortic diseases. Therefore, identification of the genetic alterations leading to these aortic diseases has the potential for early identification of individuals at risk. In addition, biochemical abnormalities involved in the progression of aortic disease are being identified through studies of patients' aortic samples and animal models of the disease.5,6 The biochemical alterations identified in the aortic tissue have the potential to serve as biomarkers for aortic disease. Understanding the molecular pathogenesis may lead to targeted therapy to prevent aortic disease. Medical and gene-based treatments are beginning to show promise for reducing or delaying catastrophic complications of thoracic aortic diseases.1.5. Glossary of Terms and Abbreviations Used Throughout the GuidelineAneurysm (or true aneurysm): a permanent localized dilatation of an artery, having at least a 50% increase in diameter compared to the expected normal diameter of the artery in question. Although all 3 layers (intima, media, and adventitia) may be present, the intima and media in large aneurysms may be so attenuated that in some sections of the wall they are undetectable.Pseudoaneurysm (or false aneurysm): contains blood resulting from disruption of the arterial wall with extravasation of blood contained by periarterial connective tissue and not by the arterial wall layers. Such an extravascular hematoma that freely communicates with the intravascular space is also known as a pulsating hematoma.7–9Ectasia: arterial dilatation less than 150% of normal arterial diameter.Arteriomegaly: diffuse arterial dilatation involving several arterial segments with an increase in diameter greater than 50% by comparison to the expected normal arterial diameter.Thoracoabdominal aneurysm (TAA): aneurysm involving the thoracic and abdominal aorta.Abdominal aortic aneurysm (AAA): aneurysm involving the infradiaphragmatic abdominal aorta.Aortic dissection (AoD): disruption of the media layer of the aorta with bleeding within and along the wall of the aorta. Dissection may, and often does, occur without an aneurysm being present. An aneurysm may, and often does, occur without dissection. The term dissecting aortic aneurysm is often used incorrectly and should be reserved only for those cases where a dissection occurs in an aneurysmal aorta.2. The Thoracic AortaThe thoracic aorta is divided into 4 parts: the aortic root (which includes the aortic valve annulus, the aortic valve cusps, and the sinuses of Valsalva); the ascending aorta (which includes the tubular portion of the ascending aorta beginning at the sinotubular junction and extending to the brachiocephalic artery origin); the aortic arch (which begins at the origin of the brachiocephalic artery, and is the origin of the head and neck arteries, coursing in front of the trachea and to the left of the esophagus and the trachea); and the descending aorta (which begins at the isthmus between the origin of the left subclavian artery and the ligamentum arteriosum and courses anterior to the vertebral column, and then through the diaphragm into the abdomen) (see Figure 1). Download figureDownload PowerPointFigure 1. Normal anatomy of the thoracoabdominal aorta with standard anatomic landmarks for reporting aortic diameter as illustrated on a volume-rendered CT image of the thoracic aorta. CT indicates computed tomographic imaging. Anatomic locations: 1, Aortic sinuses of Valsalva; 2, Sinotubular junction; 3, Mid ascending aorta (midpoint in length between Nos. 2 and 4); 4, Proximal aortic arch (aorta at the origin of the innominate artery); 5, Mid aortic arch (between left common carotid and subclavian arteries); 6, Proximal descending thoracic aorta (begins at the isthmus, approximately 2 cm distal to left subclavian artery); 7, Mid descending aorta (midpoint in length between Nos. 6 and 8); 8, Aorta at diaphragm (2 cm above the celiac axis origin); 9, Abdominal aorta at the celiac axis origin. CT indicates computed tomographic imaging.The normal human adult aortic wall is composed of 3 layers, listed from the blood flow surface outward: Intima: Endothelial layer on a basement membrane with minimal ground substance and connective tissue.Media: Bounded by an internal elastic lamina, a fenestrated sheet of elastic fibers; layers of elastic fibers arranged concentrically with interposed smooth muscle cells; bounded by an external elastic lamina, another fenestrated sheet of elastic fibers.Adventitia: A resilient layer of collagen containing the vasa vasorum and nerves. Some of the vasa vasorum can penetrate into the outer t
