American College of Radiology
Full Text Guideline
Evidence Supporting the Recommendations
The recommendations are based on analysis of the current literature and expert panel consensus.
Implementation of the Guideline
An implementation strategy was not provided.
Benefits/Harms of Implementing the Guideline Recommendations
Selection of appropriate radiologic imaging procedures for rapid and accurate diagnosis of aortic dissection
- In multiplanar transesophageal echocardiography (TEE), diagnostic problems may be encountered in the ascending aorta where reverberation artifacts can result in false positive diagnosis of dissection.
- False negative arteriograms may occur when the false lumen is not opacified, when there is simultaneous opacification of the true and false lumen, and when the intimal flap is not displayed in profile. Disadvantages of angiography are that it is invasive, iodinated contrast material is required, and angiography has limited ability to assess the surrounding structures for involvement (e.g., for the presence of mediastinal hemorrhage), which is readily detected by computed tomography.
- Compared to a dedicated computed tomography angiography (CTA) performed specifically for assessing aortic dissection, the major disadvantages of triple-rule-out CT protocol are increased contrast and radiation doses, thus limiting its applicability to a unique subset of patients in whom pulmonary embolism, aortic dissection, and acute coronary syndrome cannot be reliably clinically differentiated based on patient symptomatology.
Gadolinium-Based Contrast Agents
Nephrogenic systemic fibrosis (NSF) is a disorder with a scleroderma-like presentation and a spectrum of manifestations that can range from limited clinical sequelae to fatality. It appears to be related to both underlying severe renal dysfunction and the administration of gadolinium-based contrast agents. It has occurred primarily in patients on dialysis, rarely in patients with very limited glomerular filtration rate (GFR) (i.e., <30 mL/min/1.73 m2), and almost never in other patients. Although some controversy and lack of clarity remain, there is a consensus that it is advisable to avoid all gadolinium-based contrast agents in dialysis-dependent patients unless the possible benefits clearly outweigh the risk, and to limit the type and amount in patients with estimated GFR rates <30 mL/min/1.73 m2. For more information, please see the American College of Radiology (ACR) Manual on Contrast Media (see the "Availability of Companion Documents" field).
Relative Radiation Level
Potential adverse health effects associated with radiation exposure are an important factor to consider when selecting the appropriate imaging procedure. Because there is a wide range of radiation exposures associated with different diagnostic procedures, a relative radiation level (RRL) indication has been included for each imaging examination. The RRLs are based on effective dose, which is a radiation dose quantity that is used to estimate population total radiation risk associated with an imaging procedure. Patients in the pediatric age group are at inherently higher risk from exposure, both because of organ sensitivity and longer life expectancy (relevant to the long latency that appears to accompany radiation exposure). For these reasons, the RRL dose estimate ranges for pediatric examinations are lower as compared to those specified for adults. Additional information regarding radiation dose assessment for imaging examinations can be found in the ACR Appropriateness Criteria® Radiation Dose Assessment Introduction document (see the "Availability of Companion Documents" field).
Rating Scheme for the Strength of the Recommendations
The American College of Radiology (ACR) Committee on Appropriateness Criteria and its expert panels have developed criteria for determining appropriate imaging examinations for diagnosis and treatment of specified medical condition(s). These criteria are intended to guide radiologists, radiation oncologists, and referring physicians in making decisions regarding radiologic imaging and treatment. Generally, the complexity and severity of a patient's clinical condition should dictate the selection of appropriate imaging procedures or treatments. Only those examinations generally used for evaluation of the patient's condition are ranked. Other imaging studies necessary to evaluate other co-existent diseases or other medical consequences of this condition are not considered in this document. The availability of equipment or personnel may influence the selection of appropriate imaging procedures or treatments. Imaging techniques classified as investigational by the U.S. Food and Drug Administration (FDA) have not been considered in developing these criteria; however, study of new equipment and applications should be encouraged. The ultimate decision regarding the appropriateness of any specific radiologic examination or treatment must be made by the referring physician and radiologist in light of all the circumstances presented in an individual examination.
Searches of Electronic Databases
Literature Search Procedure
Staff search in PubMed only for peer reviewed medical literature for routine searches. Any article or guideline may be used by the author in the narrative but those materials may have been identified outside of the routine literature search process.
The Medline literature search is based on keywords provided by the topic author. The two general classes of keywords are those related to the condition (e.g., ankle pain, fever) and those that describe the diagnostic or therapeutic intervention of interest (e.g., mammography, MRI).
The search terms and parameters are manipulated to produce the most relevant, current evidence to address the American College of Radiology Appropriateness Criteria (ACR AC) topic being reviewed or developed. Combining the clinical conditions and diagnostic modalities or therapeutic procedures narrows the search to be relevant to the topic. Exploding the term "diagnostic imaging" captures relevant results for diagnostic topics.
The following criteria/limits are used in the searches.
- Articles that have abstracts available and are concerned with humans.
- Restrict the search to the year prior to the last topic update or in some cases the author of the topic may specify which year range to use in the search. For new topics, the year range is restricted to the last 10 years unless the topic author provides other instructions.
- May restrict the search to Adults only or Pediatrics only.
- Articles consisting of only summaries or case reports are often excluded from final results.
The search strategy may be revised to improve the output as needed.
The total number of source documents identified as the result of the literature search is not known.
Weighting According to a Rating Scheme (Scheme Given)
Study Quality Category Definitions
Category 1 - The study is well-designed and accounts for common biases.
Category 2 - The study is moderately well-designed and accounts for most common biases.
Category 3 - There are important study design limitations.
Category 4 - The study is not useful as primary evidence. The article may not be a clinical study or the study design is invalid, or conclusions are based on expert consensus. For example:
- The study does not meet the criteria for or is not a hypothesis-based clinical study (e.g., a book chapter or case report or case series description).
- The study may synthesize and draw conclusions about several studies such as a literature review article or book chapter but is not primary evidence.
- The study is an expert opinion or consensus document.
Review of Published Meta-Analyses
Systematic Review with Evidence Tables
The topic author drafts or revises the narrative text summarizing the evidence found in the literature. American College of Radiology (ACR) staff draft an evidence table based on the analysis of the selected literature. These tables rate the strength of the evidence (study quality) for all articles included in the narrative text.
The expert panel reviews the narrative text, evidence table, and the supporting literature for each of the topic-variant combinations and assigns an appropriateness rating for each procedure listed in the table. Each individual panel member assigns a rating based on his/her interpretation of the available evidence.
More information about the evidence table development process can be found in the ACR Appropriateness Criteria® Evidence Table Development document (see the "Availability of Companion Documents" field).
Expert Consensus (Delphi)
The appropriateness ratings for each of the procedures included in the Appropriateness Criteria topics are determined using a modified Delphi methodology. A series of surveys are conducted to elicit each panelist's expert interpretation of the evidence, based on the available data, regarding the appropriateness of an imaging or therapeutic procedure for a specific clinical scenario. American College of Radiology (ACR) staff distributes surveys to the panelists along with the evidence table and narrative. Each panelist interprets the available evidence and rates each procedure. The surveys are completed by panelists without consulting other panelists. The appropriateness rating scale is an ordinal scale that uses integers from 1 to 9 grouped into three categories: 1, 2, or 3 are in the category "usually not appropriate"; 4, 5, or 6 are in the category "may be appropriate"; and 7, 8, or 9 are in the category "usually appropriate." Each panel member assigns one rating for each procedure for a clinical scenario. The ratings assigned by each panel member are presented in a table displaying the frequency distribution of the ratings without identifying which members provided any particular rating.
If consensus is reached, the median rating is assigned as the panel's final recommendation/rating. Consensus is defined as eighty percent (80%) agreement within a rating category. A maximum of three rounds may be conducted to reach consensus. Consensus among the panel members must be achieved to determine the final rating for each procedure.
If consensus is not reached, the panel is convened by conference call. The strengths and weaknesses of each imaging procedure that has not reached consensus are discussed and a final rating is proposed. If the panelists on the call agree, the rating is proposed as the panel's consensus. The document is circulated to all the panelists to make the final determination. If consensus cannot be reached on the call or when the document is circulated, "No consensus" appears in the rating column and the reasons for this decision are added to the comment sections.
This modified Delphi method enables each panelist to express individual interpretations of the evidence and his or her expert opinion without excessive influence from fellow panelists in a simple, standardized and economical process. A more detailed explanation of the complete process can be found in additional methodology documents found on the ACR Web site (see also the "Availability of Companion Documents" field).
A formal cost analysis was not performed and published cost analyses were not reviewed.
Internal Peer Review
Criteria developed by the Expert Panels are reviewed by the American College of Radiology (ACR) Committee on Appropriateness Criteria.
Identifying Information and Availability
Jacobs JE, Latson LA Jr, Abbara S, Akers SR, Araoz PA, Cummings KW, Cury RC, Dorbala S, Earls JP, Hoffmann U, Hsu JY, Khosa F, Min JK, Woodard PK, Expert Panel on Cardiac Imaging. ACR Appropriateness CriteriaÂ® acute chest pain -- suspected aortic dissection [online publication]. Reston (VA): American College of Radiology (ACR); 2014. 11 p. [64 references]
Not applicable: The guideline was not adapted from another source.
The American College of Radiology (ACR) provided the funding and the resources for these ACR Appropriateness Criteria®.
Committee on Appropriateness Criteria, Expert Panel on Cardiac Imaging
Panel Members: Jill E. Jacobs, MD (Principal Author); Larry A. Latson Jr., MS, MD (Research Author); Suhny Abbara, MD (Panel Vice-chair); Scott R. Akers, MD; Philip A. Araoz, MD; Kristopher W. Cummings, MD; Ricardo C. Cury, MD; Sharmila Dorbala, MD; James P. Earls, MD; Udo Hoffmann, MD, MPH; Joe Y. Hsu, MD; Faisal Khosa, MD; James K. Min, MD; Pamela K. Woodard, MD (Panel Chair)
This is the current release of the guideline.
This guideline updates a previous version: Jacobs JE, Koo CW, White RD, Woodard PK, Araoz PA, Dorbala S, Ho VB, Martin ET III, Ryan T, Vogel-Claussen J, White CS, Expert Panel on Cardiac Imaging. ACR Appropriateness Criteria® acute chest pain - suspected aortic dissection. [online publication]. Reston (VA): American College of Radiology (ACR); 2011. 8 p. [52 references]
Electronic copies: Available from the American College of Radiology (ACR) Web site.
Print copies: Available from the American College of Radiology, 1891 Preston White Drive, Reston, VA 20191. Telephone: (703) 648-8900.
The following are available:
- ACR Appropriateness Criteria®. Overview. Reston (VA): American College of Radiology; 2013 Nov. 3 p. Electronic copies: Available from the American College of Radiology (ACR) Web site.
- ACR Appropriateness Criteria®. Literature search process. Reston (VA): American College of Radiology; 2013 Apr. 1 p. Electronic copies: Available from the ACR Web site.
- ACR Appropriateness Criteria®. Evidence table development – diagnostic studies. Reston (VA): American College of Radiology; 2013 Nov. 3 p. Electronic copies: Available from the ACR Web site.
- ACR Appropriateness Criteria®. Radiation dose assessment introduction. Reston (VA): American College of Radiology; 2013 Nov. 3 p. Electronic copies: Available from the ACR Web site.
- ACR Appropriateness Criteria®. Manual on contrast media. Reston (VA): American College of Radiology; 90 p. Electronic copies: Available from the ACR Web site.
- ACR Appropriateness Criteria®. Procedure information. Reston (VA): American College of Radiology; 1 p. 2013 Apr. Electronic copies: Available from the ACR Web site.
- ACR Appropriateness Criteria® acute chest pain — suspected aortic dissection. Evidence table. Reston (VA): American College of Radiology; 2014. 26 p. Electronic copies: Available from the ACR Web site.
This summary was completed by ECRI on October 26, 2000. The information was verified by the guideline developer on December 14, 2000. This summary was updated by ECRI on February 9, 2006. This summary was updated by ECRI Institute on May 17, 2007 following the U.S. Food and Drug Administration (FDA) advisory on Gadolinium-based contrast agents. This summary was updated by ECRI Institute on June 20, 2007 following the U.S. Food and Drug Administration (FDA) advisory on gadolinium-based contrast agents. This summary was updated by ECRI Institute on June 15, 2009. This summary was updated by ECRI Institute on January 13, 2011 following the U.S. Food and Drug Administration (FDA) advisory on gadolinium-based contrast agents. This summary was updated by ECRI Institute on February 7, 2012 and July 16, 2014.
Instructions for downloading, use, and reproduction of the American College of Radiology (ACR) Appropriateness Criteria® may be found on the ACR Web site.
- Acute chest pain
- Aortic dissection
Managed Care Organizations
To evaluate the appropriateness of radiologic examinations for patients with acute chest pain caused by suspected aortic dissection
Patients with acute chest pain caused by suspected aortic dissection
- X-ray chest
- Computed tomography angiography (CTA) chest and abdomen with contrast
- Magnetic resonance angiography (MRA)
- Chest and abdomen without and with contrast
- Chest and abdomen without contrast
- Echocardiography transesophageal
- Echocardiography transthoracic resting
- Aortography, chest and abdomen
- 18F-Fluorodeoxyglucose positron emission tomography (FDG-PET)/computed tomography (CT) skull base to mid-thigh
- Utility of radiologic examinations in differential diagnosis
- Sensitivity and specificity of diagnostic tests
- Mortality rate in untreated aortic dissection
ACR Appropriateness Criteria®
Clinical Condition: Acute Chest Pain—Suspected Aortic Dissection
|X-ray chest||9||This procedure should be performed if readily available at the bedside and if it does not cause delay in obtaining a CT or MRI scan. Alternative causes of chest pain may be discovered. This is not the definitive test for aortic dissection.|
|CTA chest and abdomen with contrast||9||This procedure is recommended as the definitive test in most patients with suspicion of aortic dissection.|
|MRA chest and abdomen without and with contrast||8||This procedure is an alternative to CTA for contraindication to CT (iodinated contrast), multiple prior chest CTA for similar symptoms, and in patients showing no signs of hemodynamic instability. Scanner availability and local expertise limit widespread use as there is potential for delay in diagnosis. See statement regarding contrast in text below under "Anticipated Exceptions."||O|
|US echocardiography transesophageal||8||Consider this procedure if a skilled operator is readily available.||O|
|MRA chest and abdomen without contrast||7||This procedure is an alternative to CTA for patients with contraindication to both iodinated and gadolinium contrast agents, such as in patients with renal failure, patients with multiple prior chest CTA for similar symptoms, and in patients showing no signs of hemodynamic instability. Scanner availability and local expertise limit widespread use, as there is potential for delay in diagnosis.||O|
|Aortography chest and abdomen||5|
|US echocardiography transthoracic resting||4||O|
|FDG-PET skull base to mid-thigh||3||This procedure is not recommended as the initial test. It may be useful for prognostication and for distinguishing acute from chronic dissection.|
|Rating Scale: 1,2,3 Usually not appropriate; 4,5,6 May be appropriate; 7,8,9 Usually appropriate||*Relative Radiation Level|
Note: Abbreviations used in the table are listed at the end of the "Major Recommendations" field.
Summary of Literature Review
Aortic dissection typically presents with sudden onset of excruciating, tearing, anterior, or interscapular chest pain that tends to migrate along the course of the dissection. Symptoms may be dominated by dissection-related side branch obstruction or malperfusion syndrome due to aortic obstruction by the flap. Timely diagnosis of ascending aortic dissection is crucial to permit prompt surgical management, as the early mortality rates are reported to be 1% to 2% per hour after the onset of symptoms. Mortality is high in untreated aortic dissection. The overall in-hospital mortality rate for acute aortic dissection is reported to be 12% to 27%. Medical management alone of type A aortic dissections is associated with a mortality rate of nearly 20% by 24 hours after presentation, 30% by 48 hours, 40% to 70% by day 7, and 50% by 1 month. The major cause of early death is aortic rupture. The presence of a patent false lumen has been associated with an increased risk of mortality. Classification of aortic dissection is based on the site of the intimal tear and the extent of the dissection. The clinical presentations of these various types of dissections may be quite similar.
Classification of Aortic Dissection
In DeBakey type I and type II dissection, the entrance intimal tear is located in the ascending aorta, usually just a few centimeters above the aortic valve. In type I dissection, the intimal flap extends for a variable distance beyond the aortic arch and into the descending aorta, while in type II the intimal flap is confined to the ascending aorta. Type III dissection originates in the descending aorta, usually just beyond the origin of the left subclavian artery and propagates antegrade into the descending aorta. Rarely, the entrance intimal tear occurs in an unusual location such as the abdominal aorta.
The more commonly used Stanford classification comprises 2 categories. Type A refers to any dissection involving the ascending aorta, and therefore is equivalent to DeBakey type I and type II. Type B dissection is confined to the aorta distal to the left subclavian artery and may extend to the abdominal aorta. Stanford type B dissection is therefore equivalent to DeBakey type III. Approximately two-thirds of dissections involve the ascending aorta (type A). Differentiation of the types of dissection is done by identifying the location of the intimal flap and is crucial because patients with a type A dissection of the aorta typically require surgical correction or stenting. Type B dissection is often managed medically unless the aorta is excessively dilated or there is mesenteric/limb ischemia.
Both the Stanford and DeBakey classifications are ambiguous with regard to dissections involving the descending aorta and aortic arch but sparing the ascending aorta proximal to the innominate artery. Such lesions are best described as Stanford type B or DeBakey type III with arch involvement to provide surgeons and cardiologists with the information needed to make appropriate management decisions. Reoperations after surgical repair in patients with type I and type II dissections are necessary in up to 10% of patients at 5 years and 40% of patients at 10 years.
An aortic intramural hematoma is considered a variant of classic dissection. The etiology is uncertain, but postulates include rupture of the vasa vasorum in the medial layer of the aorta. This may provoke a secondary tear and communication with the aortic lumen, converting to a dissection in 28% to 47% of patients. Intramural hematomas may extend along the aorta or may progress, regress, or reabsorb. The prevalence of intramural hematoma in patients with suspected aortic dissection is in the range of 21% to 30%. Involvement of the ascending aorta is generally considered an indication for urgent surgery because the potential complications are similar to that of dissection in this location. Penetrating aortic ulcer is another aortic condition properly considered separately from true aortic dissection, as both the pathophysiology (aortic wall disruption originating in an atherosclerotic plaque) and epidemiology (patients tend to be older, with extensive aortic atherosclerosis and a lesser degree of hypertension) differ from those of aortic dissection.
Overview of Imaging
Imaging studies in the evaluation of suspected thoracic aortic dissection should be directed toward confirming its presence; classifying the dissection as Stanford type A or B (and/or DeBakey types I, II, or III); identifying entry and reentry sites; evaluating the patency of the false lumen; detecting the presence or absence of aortic branch involvement; assessing involvement of the coronary ostia; evaluating aortic valve competency; and determining the presence or absence of extravasated blood in mediastinal, pleural, or pericardial spaces. In addition, imaging should help distinguish classic aortic dissection from other causes of "acute aortic syndrome" such as acute intramural hematoma and penetrating aortic ulcer.
The primary role of chest radiography in patients with suspected acute aortic dissection is to rule out other thoracic pathology. Although a chest radiograph is recommended in patients presenting with acute chest pain, including those suspected of having aortic dissection, a substantial portion of patients with dissection may have negative chest radiograph findings. Therefore, further imaging should be pursued despite a normal chest radiograph in cases of suspected aortic dissection. In most cases of dissection, the positive findings on a chest radiograph are nonspecific and, when studied in conjunction with the clinical history, can be significant and provide supporting evidence for dissection. Widening of the superior mediastinum, among other signs of dissection, is seen in up to 61% of patients. However, mediastinal widening may be difficult to accurately evaluate, especially with portable radiography, which tends to magnify the aorta more compared to the standard posteroanterior view. Displacement of aortic wall calcification is a finding of limited value and may be misleading. Therefore, most patients with acute chest pain and suspicion of dissection will need further noninvasive imaging despite having either a negative or positive chest radiograph.
Computed tomography (CT) with contrast injection is indicated in the diagnosis of aortic dissection. CT was the most common initial diagnostic test performed in patients enrolled in the International Registry of Acute Aortic Dissection. It is minimally invasive, faster, safer, cheaper, and less resource intensive than catheter aortography. Most larger hospitals now have in-house CT technologists available 24 hours a day for emergency studies. CT angiography (CTA) affords high-quality thin axial sections that demonstrate intimal flaps, aortic atherosclerotic plaque, branch vessel involvement, entry and reentry sites; patency of the false lumen, extravascular pathologic conditions that may cause mediastinal widening or chest symptoms, and spatial relationships and status of adjacent organs and pericardial and pleural spaces. Precontrast images are often utilized in CTA protocols for suspected aortic dissection to identify aortic calcification and intramural hematoma, and are also 71% to 94% sensitive for the detection of acute dissection.
A significant advantage of CT is that alternative causes of chest pain have been reported in up to 21% of cases scanned for suspected aortic dissection. Electrocardiographic (ECG) gating is a useful technique to reduce motion artifacts as discussed in further detail later in this document. Factors reducing the diagnostic accuracy of CTA include poor opacification of the aorta due to inadequate contrast injection or improper bolus timing, failure to identify the intimal flap because of motion artifacts, and misinterpretation of streak artifacts or motion artifacts as an intimal flap. When the false lumen does not opacify, differentiation among a thrombus-filled atherosclerotic aneurysm, thrombosed dissection, or intramural hematoma may be difficult. Other limitations of CT include the need for intravenous administration of iodinated contrast material and the use of ionizing radiation.
Numerous older studies evaluating the efficacy of CT in diagnosing aortic dissection have demonstrated sensitivities of 90% to 100%, but lower specificities ranging from 87% to 100%. However these studies evaluated conventional CT, which has largely been supplanted by faster multidetector helical CT (MDCT). More recent MDCT studies enrolling up to 57 patients have reported sensitivities and specificities of 100%. The multidetector arrays in MDCT allow accurate imaging of a large anatomic area with high resolution and a short acquisition time. MDCT permits short volumetric acquisition, facilitating patient breath-holding and thereby eliminating ventilatory misregistration. Narrow collimation results in improved resolution with improved visualization of vascular structures as compared with conventional CT. Shorter imaging times also improve bolus tracking and image acquisition during peak contrast enhancement, resulting in improved visualization of vascular structures as compared with conventional CT. CTA provides exquisite detail of the aortic anatomy, branch vessel involvement, and associated visceral pathology (ischemia/infarction). ECG gating has proven particularly valuable for minimizing ascending aortic motion artifacts that can mimic dissection without significantly increasing imaging time. In addition, ECG gating allows for qualitative assessment of aortic insufficiency and evaluation of coronary artery involvement. Type A dissection is reported to involve the coronaries in approximately 15% of patients undergoing surgery for acute type A dissection.
The rapid, large-volume acquisition that can be obtained with MDCT allows imaging of both the thoracic and abdominal components of the dissection and assessment of extension of the dissection into abdominal and pelvic branch vessels with one injection of a reasonable volume of contrast. Postprocessing of the volumetric data set using multiplanar reformatting and 3-dimensional (3-D) volume rendering facilitates evaluation of the course of the intimal flap, branch vessel, and visceral organ involvement. Recent studies show similar sensitivities for CTA, transesophageal echocardiography (TEE), and magnetic resonance imaging (MRI) in detecting aortic dissection. Evaluation of the relative accuracy of these modalities is confounded by the fact that technical improvements in CT, MRI, and TEE have outpaced the ability to perform necessary research trials. To date, there have been no large studies comparing MDCT, MRI and TEE.
Because the differential diagnosis for patients presenting with an acute chest pain syndrome is broad and often includes multiple etiologies including coronary artery disease, pulmonary embolism, and aortic dissection, triple-rule-out CT protocols are increasingly being used so that all 3 of these potentially fatal possibilities can be evaluated in a single examination. Although details of protocols vary between institutions, the general technique involves intravenous administration of iodinated contrast, the timing of which allows for assessment of both the pulmonary arteries and the aorta. The pulmonary arteries are evaluated on the initial nongated study, and the aorta, aortic root, and the coronary arteries are evaluated on the ECG-gated examination. Various techniques, such as prospective ECG triggering and tube current modulation, can be used to reduce radiation exposure. It has been reported that triple-rule-out CT can safely eliminate further diagnostic testing in over 75% of patients in the appropriate patient population. However, a recent randomized study found that the triple-rule-out protocol, though having similar diagnostic yield, did not reduce the length of stay in the emergency room, the rate of subsequent testing, or costs compared to either a dedicated coronary CTA, a dedicated CT pulmonary embolism study, or a dedicated CT dissection study.
Compared to a dedicated CTA performed specifically for assessing aortic dissection, the major disadvantages of the triple-rule-out protocol are increased contrast and radiation doses, thus limiting its applicability to a unique subset of patients in whom pulmonary embolism, aortic dissection, and acute coronary syndrome cannot be reliably clinically differentiated based on patient symptomatology. Moreover, most triple-rule-out protocols exclude the noncontrast phase of a dedicated aortic CTA, thus rendering evaluation for intramural hematoma difficult. Most triple-rule-out protocols also exclude the abdominal aorta, and as descending dissections often extend to involve the abdominal aorta, the full extent of a descending aortic dissection may not be visualized. With the introduction of newer high-pitch CT acquisition techniques, imaging times are becoming fast enough to allow for at least limited assessment of the proximal coronary arteries without ECG-gating, further reducing radiation dose. Continued clinical research is necessary to confirm appropriate utilization of the triple-rule-out examination.
Although precontrast images are recommended for identifying calcification and intramural hematoma, such a sequence may not be necessary with the advent of dual-source dual-energy multidetector CT (DECT) which enables generation of virtual noncontrast images from a single dual-energy data acquisition. However, the use of these virtual noncontrast images remains controversial. Advantages of DECT include reduction in the number of acquisition sequences performed, thereby reducing patient radiation dose. In addition, due to increased photoelectric absorption at 80 kVp, DECT may allow for a smaller volume of contrast material to be administered. Further outcomes studies are needed to assess the performance of DECT in the acute setting.
Magnetic Resonance Angiography (MRA)
MRA allows the noninvasive visualization of the thoracic and abdominal aorta in multiple projections without the use of ionizing radiation. Patients can also be imaged without the use of contrast agents if they are contraindicated. A variety of pulse sequences are available. ECG-triggered black-blood or white-blood images provide exquisite anatomic detail of the heart and aorta. Cine MRI and other fast-gradient-echo techniques allow visualization of flowing blood, facilitating the differentiation of slow flowing blood and clot, and determination of the presence of aortic insufficiency. The true and false lumen and intimal flap are readily identified. Functional cardiac information such as aortic regurgitation and left ventricular function can be assessed. Newer gadolinium-contrast-enhanced 3-D MRA (CE-MRA) techniques permit rapid acquisition of MR angiograms of the thoracic and abdominal aorta and their branch vessels. These techniques allow coverage of large volumes with and without breath holding, and 3-D data sets may be reconstructed. 3-D CE-MRA permits easy identification of both the true and false lumen and enables identification of the type of dissection and assessment of patency of the false lumen. A unique advantage of gated white-blood MRI techniques is that these can demonstrate whether the intimal flap is causing organ ischemia by occluding the flow of blood to a branch vessel during the cardiac cycle (usually systole).
MRI is considered a very accurate technique for diagnosing aortic dissection. Both the sensitivity and specificity of MRI for diagnosing aortic dissection have recently been reported to be 100%. For identifying the site of entry, sensitivity was 85% and specificity 100%, and for identifying thrombus and the presence of a pericardial effusion, sensitivity and specificity were both 100%. Excellent sensitivity (92% to 98%) and specificity (100%) have been documented for CE-MRA in acute and chronic aortic dissection. Limitations of MRI are longer examination times compared with MDCT and more limited scanner availability on an emergency basis. Studies in uncooperative patients and patients who are unable to hold their breath can result in nondiagnostic images. The use of cardiac gating may be limited in the presence of cardiac arrhythmias. Further, patients with cardiac pacemakers, ferromagnetic aneurysm clips, and other MRI-incompatible devices cannot undergo MRI. Newer "MR conditional" pacemakers are being developed, but these have not yet reached widespread use.
Monitoring and treatment of very ill patients are also more difficult in the MRI environment compared with CT. Faster MRI techniques are being explored, and as the newer generations of faster scanners are developed, the feasibility of scanning these patients emergently is expected to improve. Importantly, gadolinium-based contrast agents are contraindicated in patients with severe renal insufficiency due to the risk of nephrogenic systemic fibrosis. In patients with renal insufficiency, in whom both iodinated CT contrast agents and gadolinium-based MR contrast agents may be contraindicated, noncontrast MR using sequences such as ECG-gated cine true-fast imaging with steady state precession and respiratory-gated 3-D steady state free precession have been shown to be as accurate as contrast-enhanced MRA in the diagnosis of acute aortic syndromes.
In the diagnosis of aortic dissection, echocardiography has the advantages of being readily available and suitable for use at the bedside in hemodynamically unstable patients. Transthoracic echocardiography (TTE) has been found to have a sensitivity of 59% to 85% and a specificity of 93% to 96%. It is useful in the diagnosis of dissection involving the ascending aorta and can diagnose the hemodynamic significance of pericardial effusions, the degree of aortic regurgitation, and left ventricular function. TTE is of marginal value in diagnosing distal dissections because of the limited availability of ultrasound (US) windows. Although the sensitivity of TTE in detecting descending aortic dissections was previously reported to be lower (31%-80%) than contrast-enhanced CT and MRI, recent technical innovations such as harmonic imaging and microbubble contrast enhancement have been demonstrated to improve the sensitivity of TTE in detecting descending dissections to 84%.
TEE overcomes many of the limitations of TTE and can image almost the entire thoracic aorta with limited visualization of the distal ascending aorta and arch vessels. TEE has sensitivity similar to that of MRI and CT for detecting dissection, and it is also useful for detecting associated coronary artery involvement.
Multiplanar TEE can accurately diagnose aortic dissection with a sensitivity, specificity, and negative predictive values of up to 100%. Principal limitations of TEE are its dependence on a high degree of operator skill and blind areas in the distal ascending aorta and proximal transverse arch that are obscured by the air-containing trachea and left main bronchus. Diagnostic problems may also be encountered in the ascending aorta where reverberation artifacts can result in false-positive diagnosis of dissection. Additional limitations include the inability to visualize the distal extent of the dissection in the abdomen. Nonetheless, in most cases of acute dissection, TEE provides immediate, sufficient information to determine whether surgical intervention is indicated. Additionally, in hemodynamically unstable individuals, TEE can be safely performed with topical anesthetic alone. In descending aortic dissection, angiography, CT, and MRI are preferable, because they allow evaluation of branch vessel involvement and assessment of the distal extension of the dissection.
Intravascular US has been explored for evaluating aortic dissection. However, it is an invasive procedure, and its use has been limited to intraoperative or postoperative evaluation of aortic dissection. Presently, intravascular US has no role in the immediate evaluation of suspected acute aortic syndrome.
Angiography has historically been considered the gold standard for diagnosing aortic dissection with sensitivity, specificity, positive predictive value, and negative predictive value of 88%, 94%, 96%, and 84%, respectively.
The diagnostic accuracy of digital subtraction angiography approaches 98% in some series. Angiography permits management of critically ill patients, and aortic regurgitation and aortic branch vessel involvement (including the coronary arteries) can be assessed. High frame rates facilitate identification of the intimal tear and the degree of aortic insufficiency. False negative arteriograms may occur when the false lumen is not opacified, when there is simultaneous opacification of the true and false lumen, and when the intimal flap is not displayed in profile.
Disadvantages of angiography are that it is invasive, iodinated contrast material is required, and angiography has limited ability to assess the surrounding structures for involvement (e.g., for the presence of mediastinal hemorrhage), which is readily detected by CT. Although angiography provides good visualization of the thoracic and abdominal branch vessels and flow patterns, it is now rarely used as the evaluation and management of aortic dissection except where definitive coronary evaluation is required. In recent years, it has been largely replaced by minimally invasive TEE and noninvasive CT and MRI. More recently, with the development of so-called "hybrid" operating rooms, which are fully-equipped operating rooms that also include the capability for performing both diagnostic angiographic and therapeutic endovascular procedures, preoperative angiographic assessment of the coronary arteries and sites of visceral malperfusion is feasible without adding a large time delay between angiography and definitive therapy.
18F-Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography
18F-Fluorodeoxyglucose positron emission tomography (FDG-PET)/CT has recently been explored for evaluation of aortic dissection and has been shown to be of value in distinguishing acute from chronic dissection. In addition, several studies have also shown that elevated FDG uptake of mean standardized uptake value in the region of the dissection flap is predictive of poor outcome.
Several studies reported that increased FDG avidity in the atherosclerotic vascular wall correlated with dense infiltrations of macrophages and the number of macrophages in the plaque. These results support the hypothesis that the uptake of FDG is predictive of elevated concentrations of macrophages and serves as a marker of atherosclerotic inflammation within the aortic wall. Other studies have demonstrated a relationship between the degree of inflammation (as measured by serum C-reactive protein levels) and vascular complications and/or poor outcome in patients with acute aortic dissection.
A significant disadvantage of FDG-PET/CT is the prolonged scan time, thus obviating its applicability in the acute setting. In addition, as the available data are limited to small studies, this modality has limited value until results from larger studies become available. Potentially, FDG-PET/CT may play a role in prognosticating the outcome in individuals diagnosed with aortic dissection. Further investigation is warranted.
- Because patients with acute dissection are critically ill and potentially in need of emergency operation, the selection of a given modality will depend on clinical circumstances and availability.
- Current experience suggests that the accuracies of TEE (performed by a skilled operator and reader), MDCT, and MRI are very similar.
- CTA is likely to be more rapidly available on a 24-hour basis and is associated with less patient discomfort. It can provide information on branch vessel involvement and ancillary significant findings and has the advantage of evaluating the aorta, branch vessels, and visceral organs in their entirety. Although it does not provide information regarding aortic insufficiency, this information can be obtained with TTE or TEE, if needed, while the operating room is being prepared.
- In selected centers where experienced cardiologists are readily available to perform TEE in the emergency room or in instances where hemodynamic or other clinical factors preclude CTA, TEE may be the preferred first-line imaging study because it can provide sufficient information to determine whether emergency surgery is needed.
- When information about branch vessel involvement is required by the surgeon and not provided by CTA (a rare occurrence with MDCT units), angiography may be useful. Coronary angiography may still be required if definitive preoperative coronary evaluation is needed and was suboptimally assessed on the prior MDCT, MRI, or TTE examination.
- MRA may be sufficient to replace angiography in stable patients and in patients with chronic dissection or uncertain diagnoses. In selected centers, MRA may readily be offered as the first line of imaging on an emergent basis. Faster imaging sequences may enable its use to less stable patients. In patients with renal insufficiency who cannot receive either iodinated or gadolinium-based contrast agents, the development of newer ECG- and respiratory-gated noncontrast MRA sequences can provide detailed diagnostic evaluation of the aorta comparable to that of contrast-enhanced MRA.
- Image postprocessing of CT and MRI data using multiplanar image reformatting and 3-D volume rendering may provide additional useful information for treatment planning.
Nephrogenic systemic fibrosis (NSF) is a disorder with a scleroderma-like presentation and a spectrum of manifestations that can range from limited clinical sequelae to fatality. It appears to be related to both underlying severe renal dysfunction and the administration of gadolinium-based contrast agents. It has occurred primarily in patients on dialysis, rarely in patients with very limited glomerular filtration rate (GFR) (i.e., <30 mL/min/1.73 m2), and almost never in other patients. There is growing literature regarding NSF. Although some controversy and lack of clarity remain, there is a consensus that it is advisable to avoid all gadolinium-based contrast agents in dialysis-dependent patients unless the possible benefits clearly outweigh the risk, and to limit the type and amount in patients with estimated GFR rates <30 mL/min/1.73 m2. For more information, please see the American College of Radiology (ACR) Manual on Contrast Media (see the "Availability of Companion Documents" field).
- CT, computed tomography
- CTA, computed tomography angiography
- FDG-PET, 18F-Fluorodeoxyglucose positron emission tomography
- MRA, magnetic resonance angiography
- MRI, magnetic resonance imaging
- US, ultrasound
Relative Radiation Level Designations
|Relative Radiation Level*||Adult Effective Dose Estimate Range||Pediatric Effective Dose Estimate Range|
|O||0 mSv||0 mSv|
|<0.1 mSv||<0.03 mSv|
|0.1-1 mSv||0.03-0.3 mSv|
|1-10 mSv||0.3-3 mSv|
|10-30 mSv||3-10 mSv|
|30-100 mSv||10-30 mSv|
|*RRL assignments for some of the examinations cannot be made, because the actual patient doses in these procedures vary as a function of a number of factors (e.g., region of the body exposed to ionizing radiation, the imaging guidance that is used). The RRLs for these examinations are designated as "Varies."|
Algorithms were not developed from criteria guidelines.
Patients with cardiac pacemakers, ferromagnetic aneurysm clips, and other magnetic resonance imaging (MRI) incompatible devices cannot undergo MRI, and iodinated and gadolinium-based contrast cannot be used in patients with severe renal insufficiency.
Institute of Medicine (IOM) National Healthcare Quality Report Categories
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