* Identify the types of aortic emergencies and their precipitating factors.
* Describe diagnostic imaging approaches for aortic emergencies.
* List the regions of the aorta most often affected by dissections and aneurysms.
* Explain the classification systems for aortic dissections.
* Recognize the clinical signs and symptoms of aortic emergencies.
Each year, aortic aneurysms and dissections hospitalize 67 000 Americans and kill 16 000. (1) These and other life-threatening aortic emergencies often involve acute noncardiac chest pain--a symptom of diseases and disorders not only of the aorta, but also of the respiratory system, gastrointestinal tract and musculoskeletal system. Only a third of patients presenting with noncardiac chest pain have aortic emergencies; (2) therefore, aortic emergencies are easily misinterpreted. For example, up to 38% of aortic dissections are initially undiagnosed or misdiagnosed, and in up to 28% of cases, aortic dissection is recognized only during autopsy. (1,3,4)
Effective intervention in aortic emergencies requires rapid determination of the underlying disease. Accurate diagnosis and assessment of aortic dissection, aneurysm or other life-threatening aortic emergencies involve the combined use of clinical symptoms and patient history, screening tests, and diagnostic imaging. Imaging allows rapid exclusion of other potential causes of clinical symptoms, as well as a precise determination of the nature and extent of aortic disorders.
Aortic Functional Anatomy
The aorta is the complex and dynamic root of the body's immense vascular tree. (See Fig. 1.) It arises from the heart's left ventricle at the thoracic midline, ascends to the right (the ascending aorta) and then bows dramatically to the left and toward the back (the aortic arch). Distal to the arch, the descending aorta follows the left side of the trachea and spine downward. Major arterial branches bifurcate from the aortic arch to supply oxygenated blood to the body's various anatomic regions. Although this is the most common arrangement, there are major variations in aortic arch anatomy. For example, the aorta may arch to the right instead of left, or the aortic arch may be partially bypassed by a secondary large arch vessel.
[FIGURE 1 OMITTED]
The aortic wall is composed of 3 tissue layers: the endothelial-lined intima, the elastin-rich media and the adventitia. The elastic tissues of the media layer permit the aorta to absorb the considerable, constant forces exerted by blood ejected from the heart's left ventricle. With each heartbeat, blood is pumped forcefully from the left ventricle, stretching the aorta. Energy is momentarily absorbed from the moving blood by the aorta's elastic tissues. Then, during diastole, the aortic wall recoils, transferring energy stored in the aortic wall back to the blood, propelling it upward through the aortic arch and toward the arterial system.
With age, mechanical wear and tear causes the aortic lumen to expand and the arch to stretch and straighten. These changes are called "ectasia" and are considered a normal part of aging.
Acute Aortic Disease
Aortic diseases may be congenital or acquired during a patient's lifetime. Acquired aortic disorders include atherosclerosis, aortitis (aortic inflammation, sometimes caused by syphilis or healing from physical trauma) and trauma. Cystic medial degeneration also can lead to aortic dilation and increased aortic rigidity among the elderly. Aortic dissections and aneurysms are commonly acquired aortic disorders that can lead to catastrophic emergencies. Aortic disease involves unspecific clinical symptoms such as sudden-onset chest pain (the most common symptom). Rapid identification of aortic emergencies is crucial for patient survival.
Aortic dissection usually occurs when blood enters the aortic wall under high pressure through small intimal tears, forcing apart the planes of the tissue layers to create a secondary or "false" lumen. These tears tend to develop near the aortic valve along the right anterolateral wall of the ascending aorta or in the proximal descending thoracic aorta, where blood pressure exerts the greatest forces on aortic tissues. (1)
Aortic dissection is considered to be acute if symptom onset occurred within 2 weeks of presentation, whereas patients with symptoms lasting longer than 2 weeks are considered to have chronic dissection. (1)
Dissections can extend into the aortic root, triggering aortic insufficiency. They also may develop into life-threatening ruptures by tearing through the remaining layers of aortic wall. Re-entry tears are also common, allowing blood to flow between the dissection lumen and the true aortic lumen. (2) Aneurysms with large thrombi from aortic dissections often mimic aortic dissections.
The incidence of acute aortic dissection is unclear, but estimates suggest an annual rate of up to 30 cases per 1 million Americans. (3,5) Men are between 2 and 3 times more likely to suffer aortic dissection than women. (1,4,5) In men and women younger than age 55, proximal dissection is the most frequent form of aortic dissection; among patients older than 60, distal dissection is more common. (5) Predisposing factors for acute aortic dissection include advanced age, chronic hypertension and underlying aortic diseases, including arteritis, aortic arch hyperplasia, stenosis, a bicuspid aortic valve and trauma.
Intramural Hematoma, Penetrating Ulcers and Acute Aortic Syndrome
Intramural hematoma is a distinct type of aortic dissection, distinguished by the absence of an entrance tear. (6,7) Thoracic intramural hematoma, penetrating ulcer and aortic dissection share clinical symptoms and patterns of progression, and are therefore collectively referred to as acute aortic syndrome (AAS) by some authors. (6,8)
Penetrating ulcers develop when atherosclerotic lesions enter the elastic lamina in the aortic wall's media. When patients present with classic clinical symptoms of dissection and a history of advanced atherosclerosis or tobacco smoking, penetrating ulcers are suspected. In 40% of patients with penetrating ulcers, abdominal aortic aneurysms also occur, and their location and extent must be identified as quickly as possible. (9)
Classification of Aortic Dissections
Classification systems have been devised to facilitate rapid clinical assessment of aortic dissections. (See Table 1.) Of these, the Stanford classification scheme is used most frequently. (10) Stanford type A dissections involve the ascending aorta, regardless of the dissection's origin or if other regions of the aorta are involved. (1) (See Figs. 2 and 3.) Stanford type B dissections involve aortic tissue distal to the left subclavian artery origin. (1) Because the Stanford classification scheme (and the older DeBakey system) fails to categorize aortic arch dissections, Khan et al (11) recently proposed a more inclusive classification system that defines dissections as distal if they are limited to aortic tissue distal to the left subclavian artery origin, and proximal if the dissection is proximal to the left subclavian artery origin.
[FIGURES 2-3 OMITTED]
Clinical factors correlate imperfectly with dissection type. Hypertension is present in only half of aortic dissection patients, but hypertension is far more often a predisposing factor in Stanford type A dissections (70% of cases) than type B dissections (35% of cases). (1,12) Anterior chest pain is more common in Stanford type A dissection; back and abdominal pain occur more often in patients with Stanford type B dissection. (1) However, symptoms of type A and B dissections overlap considerably, and the correlations described above are insufficiently strong to serve as reliable diagnostic factors. Rather, they are rules of thumb that, along with other clinical signs and patient history, may be useful for guiding the diagnostic process. (12) No clinical exam alone can exclude acute aortic dissection. Echocardiographic exams reveal clear abnormalities in only 40% of patients. (1)
In some patients, a combination of unusual symptoms does provide specific clinical evidence of dissection. This is because expanding dissection lumens can occlude aortic branches to the brain's blood supply, causing brain ischemia (stroke) in up to 15% of aortic dissection patients. (12) Therefore, acute chest pain occurring with new neurological deficits, such as arm or leg parasthesia or voice change, is strongly indicative of aortic dissection. (13)
Treatment of Aortic Dissections
The immediate goal of aortic dissection intervention is to reduce arterial blood pressure and the speed of left ventricle blood ejection into the aorta. After dissection is confirmed, surgery is urgently required. Stanford type A dissections require immediate surgical intervention to remove damaged aortic tissue and avoid catastrophic rupture. Most type A dissection surgeries involve graft replacement of the damaged aorta and reinforcement of the surgical margins with Teflon felt. (1) The graft is sewn to the reinforcements, which absorb some of the stress that would otherwise be exerted by blood flow onto the graft's margins.
Type B dissection surgery can cause spinal cord ischemia; in fact, these dissections are often treated medically rather than surgically, unless disease progression makes aortic rupture probable. Surgery is required if resolving acute dissection causes the development of aortic aneurysms. Patients who survive aortic dissection must undergo long-term beta blocker and statin therapies, and routine follow-up imaging exams. (14)
Endovascular stent graft (ESG) surgical techniques are gaining popularity and promise to help significantly reduce surgical mortality in patients with aortic dissection or aneurysm. (15) Follow-up computed tomography (CT) scans are used to monitor the continuing integrity of stent grafts and adjacent aortic tissue. (See Fig. 4.) ESG is used primarily for thoracic or abdominal aortic disease.
[FIGURE 4 OMITTED]
Diagnostic Imaging of Aortic Dissection
Effective medical intervention depends on the accurate and timely determination of the type and anatomic extent of dissection and precipitating intimal tears, occlusions, branch artery involvement and the dimensions of false lumens. (1) Because clinical symptoms are unspecific and reliable screening techniques do not exist, diagnostic imaging is considered mandatory when dissection is suspected.
An anteroposterior chest radiograph is often the first imaging examination ordered for patients with acute chest trauma or chest pain. (16,17) Chest radiographs of aortic dissection are commonly abnormal, with mediastinal widening, pleural effusion, and abnormal mediastinal and aortic contours constituting the most common findings. (1,12) However, the radiographic signs of aortic emergency offer poor overall specificity (86%) and sensitivity (64%) for aortic dissection and aneurysm. (18) One meta-analysis of individual radiographic signs of aortic dissection found that chest radiography has a sensitivity of only 16% for pleural effusion. (13) Disturbingly, in many patients with aortic dissection, chest radiographs will appear normal. (17,19)
Alternatives to traditional aortography such as computed tomography (CT), magnetic resonance (MR) imaging and transesophageal echocardiography (TEE) are now preferred as sensitive and specific modalities for assessing suspected aortic dissections. Helical CT, TEE, and MR angiography (MRA) all offer sensitivities up to 100% and specifities between 85% and 100% for dissection. (1) In comparison, invasive aortography is more time consuming and yields a sensitivity of up to only 89% and a specificity of up to 94%. (1)
CT is the modality of choice in most acute aortic imaging settings, but choice of imaging technique varies depending on availability, expertise in image interpretation and patient stability. Regardless of imaging modality, the main criterion to confirm aortic dissection is the presence of an intimal flap in the aorta that separates the lumens (the false and the true lumens). Widening of the aorta, compression of the true lumen and aortic wall thickening are other common findings. (2)
Anatomic structures outside the aorta can be mistaken for false lumens, increasing the risk of misdiagnosis. For example, the left intercostals vein, left superior pulmonary vein and superior pericardial recess can all appear to be false aortic lumens. (2,20)
Aortic intramural hematoma is considered a type or variant of aortic dissection, but it sometimes occurs as a primary event in patients with hypertension, when vessels supplying the aortic wall rupture and weaken aortic tissues. Intramural hematoma is imaged with TEE, CT, or less commonly with MR, and is characterized by circular local aortic wall thickening and the absence of a visible intimal flap. In TEE, intramural hematoma is seen as layered thickening of the aortic wall. (21)
Penetrating atherosclerotic ulcers are demonstrated on CT, MR and TEE as an outward pouching of the aortic wall. (2) Penetrating ulcers and associated aortic aneurysms typically occur in the descending aorta; on contrast-enhanced CT scans, margins are particularly well defined and the ulcer clearly projects beyond (outside of) the aortic lumen. (2,22)
TEE is a safe and accurate bedside alternative--initial or follow-up--imaging modality. (19) TEE visualizes aortic branch vessel involvement (1) and is particularly well suited for identifying a moving intimal flap that divides the true aortic lumen and the acquired false lumen. "Cobweb" signs--residual strands of media tissue that have not been sheared from the aortic wall--delineate the false lumen of a dissection. (19)
Peak blood flow velocity in the true aortic lumen occurs early in systole; flow in the false lumen peaks in late systole or diastole. Slow swirling of blood flow also may be noted in the false lumen.
A limitation of TEE imaging is that it produces a "blind spot" where the aortic arch meets the ascending aorta that is obscured by the trachea and left main bronchus. (17,19) Nevertheless, it is very useful for visualization of the aortic valve and intimal flap.
CT aortography produces rapid scans that have excellent spatial precision of large anatomic areas; it is now the preferred imaging modality for aortic dissection assessment. CT is the first-line imaging modality in a third of all suspected cases of dissection. (13) MRA may be diagnostically superior in some regards, but CT is widely available at emergency medical facilities and can be employed more rapidly. (1,17) Helical CT with a contrast agent minimizes respiratory motion artifacts and yields sufficiently precise data about the anatomic extent of dissections to inform surgical decisions.
Contrast-enhanced CT scans visualize the intimal flap as a thin, curved lucency within the aorta. However, CT less reliably identifies the originating intimal tear than MRA. (1) CT also commonly fails to visualize branch artery or aortic valve involvement at the aortic arch; (17) therefore, after dissection has been confirmed and initially described by CT, follow-up imaging exams with another modality may be required.
MR imaging clearly demonstrates the extent of arch and branch vessel dissection, as well as intimal tear location; it seems to offer the highest sensitivity and specificity for dissection of all imaging modalities. (19,23) However, MRA is rarely used in suspected aortic emergencies because of scan durations and difficulty accessing and monitoring the patient during scan acquisition.
When available, ECG-gated phase-contrast MRA cine techniques offer excellent visualization of flow dynamics within dissection and aortic lumens. As faster MRA techniques become available, it will probably become the preferred imaging modality for aortic dissection assessment. (11)
Aortic aneurysms develop after damage to or degeneration of the elastin in the media layer of aortic tissue and can be clinically asymptomatic. Whereas generalized aortic insufficiency involves dilation anywhere in (or throughout) the aorta, aortic aneurysms involve only focal aortic dilations and entail abnormal expansion of all 3 layers of the vessel wall) In contrast, pseudoaneurysms are focal enlargements of only the media layer.
Systemic hypertension is believed to be a major factor in the formation of true aneurysms, degrading the integrity of media elastic tissue fibers. This process leads to aneurysm formation and rupture. Ruptures are responsible for a third of aneurysm-related deaths. (24) Rupture risk is directly related to aneurysm diameter; the rupture rate for aneurysms smaller than 5 cm is 2.3%, whereas ruptures occur in 44% of aneurysms with diameters exceeding 10 cm. (25)
The primary cause of aortic aneurysms is believed to be atherosclerosis, although causal mechanisms remain unclear. Atherosclerosis-related aneurysms typically occur in or distal to the aortic arch. Aortic aneurysms can also result from progressive age-related ectasia, trauma or congenital anomalies. (See Table 2.)
Aortic aneurysms are typically spindle shaped and are classified as either thoracic or abdominal. Thoracic aortic aneurysms (TAAs) are less common than abdominal aortic aneurysms (AAAs) and involve the ascending or descending aorta or the aortic arch. Half originate in the ascending aorta and 40% in the descending aorta. (26) Some cases involve both. TAAs are most common among men between the ages of 50 and 70.
Compression of adjacent tissues by TAAs causes chest pain; compression of the laryngeal nerves can cause vocal hoarseness or laryngeal paralysis. (24,27) Ascending TAAs are often caused by advanced degradation of elastic tissue fiber, a condition associated with Marfan syndrome, an inherited cardiovascular disorder.
By definition, abdominal aortic dilation to more than 3 cm is aneurysmic. AAAs occur up to 5 times more frequently among men than women and involve genetic susceptibilities. Almost all cases (over 90%) are attributable to atherosclerosis. (24) Prognosis is poor due to a high probability of rupture; 5-year survival rates are below 20%. (24)
Although most patients with AAAs are asymptomatic, some report back or abdominal pain, or even feel abdominal pulsation. The main clinical sign of AAA is a pulsating mass in the abdomen. (24) Pain in the chest, groin or leg, nausea, difficult or labored breathing and constipation also are reported among these patients.
A small proportion of aortic aneurysms (about 3%) are thoracoabdominal, involving both thoracic and abdominal reaches of the aorta. These are diffusely atherosclerotic and ecstatic, and typically involve 1 or more variable-sized aneurysmic foci. (24)
Unless surgical intervention is undertaken, patients with TAAs and thoracoabdominal aortic aneurysms have an average survival time of less than 3 years from diagnosis. (1) Up to a third of untreated patients experience aortic rupture within a month of diagnosis and, of these patients, 90% die). (1,28)
Imaging Aortic Aneurysms
As is the case in suspected cases of aortic dissection, aortic aneurysm requires careful diagnostic imaging to confirm the diagnosis and determine the aneurysm's extent and severity. Portable chest radiography is commonly the first imaging examination ordered for patients with suspected TAA. (1)
Until recently, contrast angiography was the principal definitive diagnostic imaging test for suspected TAA and preoperative measurement of the aneurysm. However, CT and MRA are noninvasive alternatives that allow sensitive and specific assessment of the extent and structure of both TAAs and AAAs. (29)
Helical CT is now the initial study of choice for TAA, matching the sensitivity and specificity of angiography and doing so more rapidly than is currently possible with MRA. Helical CT also generates 3-D images and detailed visualization of TAA branch vessel involvement. (1)
Bedside ultrasound is the preferred diagnostic imaging modality for AAA, particularly if rupture is suspected. Ultrasonography's sensitivity nears 100%, although helical CT more accurately demonstrates aneurysm dimensions. (1,24) Both MRA and CT may fail to detect aortic branch vessel occlusions.
The extent of suspected thoracoabdominal aneurysms can be visualized using a combination of anteroposterior radiography and computed tomography angiography (CTA).
Acute Traumatic Aortic Injury
Acute traumatic aortic injury (ATAI) is commonly seen in victims of motor vehicle crashes; it involves aortic wall tearing from the intima to the adventitia. (16) Death is rapid in fatal ATAI cases, usually occurring within 2 hours of the accident. (16)
Because of the limited period of time a patient can be saved, suspected ATAI is usually imaged only with chest radiography before emergency open thoracic surgery. Mediastinal hemorrhage appears on anteroposterior chest radiographs as abnormal aortic arch contours or as an obscured or abnormal contour for the descending aorta. Other signs of ATAI include widening of the right paratracheal soft tissue, widened paraspinal line and rightward displacement of the trachea or esophagus. The presence of these radiographic signs is only weakly (20%) predictive of ATAI, but their total absence has nearly perfect negative predictive power--meaning that if no such signs are evident, ATAI is almost certainly not present. (16)
Patients who survive the first 2 hours of hospitalization are less likely to experience spontaneous aortic rupture and can undergo more precise imaging examinations such as CT. If a CT scanner is unavailable, or if CT reveals periaortic blood but no evidence of aortic damage, conventional aortography is indicated. (30,31) However, aortography is time consuming; delaying surgery to allow for aortographic examination may result in a lethal rupture before surgical intervention. Endovascular surgical techniques are gaining popularity and promise to improve morbidity and mortality rates associated with ATAI.
Acute Aortic Occlusion
Occlusive disease of the aorta can lead to acute symptoms similar to those seen in other aortic emergencies. Acute aortic occlusion is rare and is caused by arterial embolism of cardiac origin or by advanced atherosclerosis-related thrombosis. (1) Chronic arterial insufficiency is not commonly an emergency, but acute aortic occlusion requires prompt surgical intervention. (1) Clinical symptoms include weakness and the "6 Ps": pain, pallor, paresthesias, paralysis, poikilothermia (disruption of normal thermoregulatory function) and lower-extremity pulselessness. (1)
Acute aortic occlusion is usually diagnosed based on clinical data and patient history, but imaging exams can confirm the diagnosis and help locate the occlusion and its extent. Invasive contrast digital subtraction angiography (DSA) sometimes is used to determine aortic patency. More commonly, helical CT--which is faster and noninvasive--accurately identifies large aortic thrombi, which are a common underlying cause of emboli. (1)
Typically, patients are administered heparin and undergo aortobifemoral bypass graft surgery or, more rarely, percutaneous transluminal angioplasty. If clinical evidence can localize the probable embolism, catheter embolectomy is undertaken without an imaging examination because imaging would delay definitive treatment and increase tissue damage caused by prolonged ischemia. Only then is follow-up imaging conducted to confirm the nature of the embolism and whether additional surgery is warranted. (1)
In stable patients, MRA is quickly becoming the imaging modality of choice because it is rapid and less invasive, and offers sensitivity and specificity similar to that obtained with DSA. (31,32) Bedside transabdominal duplex ultrasonography is used to assess abdominal aortic involvement and TEE can rapidly assess thoracic aortic thrombi. (33)
Rapid assessment of aortic emergencies is crucial for effective, life-saving surgical intervention. Traditional aortographic imaging was too slow and involved for use in patients experiencing aortic emergencies. With the emergence of fast, high-resolution noninvasive and minimally invasive
cross-sectional imaging techniques, aortography is quickly becoming an outdated imaging modality for acute settings. CT and TEE, combined as necessary to capitalize on each modality's strengths and, increasingly, MRA allow detailed assessment of aortic integrity and the extent and nature of aortic emergencies. As techniques are better refined for acute aortic imaging, diagnostic imaging will become more important in the timely assessment and intervention of life-threatening aortic catastrophes. Imaging will continue to play a central role in follow-up monitoring of graft integrity and disease progression, as well.
Directed Reading Continuing Education Quiz
DRI0005014 Expiration Date: Oct. 31, 2007 * Approved for 1.5 Cat. A CE credits
To receive Category A continuing education credit for this Directed Reading, read the preceding article and circle the correct response to each statement. Choose the answer that is most correct based on the text. Transfer your responses to the answer sheet on Page 74 and then follow the directions for submitting the answer sheet to the American Society of Radiologic Technologists. You also may take Directed Reading quizzes online at www.asrt.org. Effective October 1, 2002, new and reinstated members are ineligible to take DRs from journals published prior to their most recent join date unless they have purchased a back issue from ASRT.
* Your answer sheet for this Directed Reading must be received in the ASRT office on or before this date.
1. Annually, -- Americans are hospitalized with aortic dissections and aneurysms and -- die.
a. 67000; 16000
b. 56000; 13000
c. 45000; 10000
d. 34000; 7000
2. Up to -- % of aortic dissections are initially undiagnosed or misdiagnosed; in up to -- % of cases, aortic dissection is recognized only after the patient dies.
a. 18; 4
b. 28; 14
c. 28; 24
d. 48; 34
3. The aortic wall is composed of which of the following tissue layers?
a. 1 and 2
b. 1 and 3
c. 2 and 3
d. 1, 2 and 3
4. Aortic dissection is considered acute if symptom onset occurred within--weeks of presentation.
5. Some authors refer to which of the following as acute aortic syndrome (AAS)?
1. thoracic intramural hematoma
2. penetrating ulcer
3. aortic dissection
a. 1 and 2
b. 1 and 3
c. 2 and 3
d. 1, 2 and 3
6. Most type--dissection surgical interventions involve graft replacement of damaged aortic tissue and reinforcement of surgical margins with Teflon felt.
7. When dissection is suspected, clinical symptoms alone may be sufficient for reliable diagnosis.
8. Chest radiographic indications of aortic dissection and aneurysm yield an overall sensitivity of -- %.
9. In many patients with aortic dissection, -- images will appear normal.
a. chest radiograph
b. computed tomography (CT)
c. magnetic resonance angiography (MRA)
d. transesophageal echocardiography (TEE)
10. Regardless of imaging modality, the mare criterion for confirming aortic dissection is the presence of --.
a. an intimal flap
b. disjunct calcifications
c. flow regurgitation
d. aortic wall out-pouching
11. Penetrating ulcers and associated aortic aneurysms typically occur in the --.
a. aortic arch
b. ascending aorta
c. descending aorta
d. aortic valve
12. The "cobweb" sign in TEE is a marker of the -- lumen and is composed of residual strands of -- tissue.
a. true; media
b. false; media
c. true; intima
d. false; intima
13. Peak blood flow velocity in the true aortic lumen occurs in --, whereas flow in a false lumen tends to peak in --.
a. late systole; early systole
b. diastole; early systole
c. early systole; late systole
d. diastole; late systole
14. A limitation of -- is that it produces a "blind spot" where the aortic arch meets the ascending aorta.
15. TAAs are -- common than AAAs, and -- occur in the ascending aorta.
a. more; do not
b. less; do not
c. more; commonly
d. less; commonly
16. Patients with -- may report back, groin or leg pain, nausea, or a sensation of abdominal pulsation.
a. type A dissection
b. abdominal aortic aneurysm (AAA)
c. Type B dissection
d. thoracic aortic aneurysm (TAA)
17. Which of the following is currently the modality of choice for initial studies of suspected TAA?
b. helical CT
18. Acute traumatic aortic injury (ATAI) is usually imaged with -- before emergency surgical intervention.
a. chest radiography
19. Clinical symptoms of acute aortic occlusion may include all the following except:
d. upper-extremity pulselessness.
20. For stable patients with acute aortic occlusion, -- is quickly becoming a modality of choice because it is less invasive and faster than digital subtraction angiography, while offering similar diagnostic sensitivity and specificity.
BRYANT FURLOW, B.A.
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Bryant Furlow is a freelance medical writer living in northern California.
Reprint requests may be sent to the American Society of Radiologic Technologists, Communications Department, 15000 Central Ave. SE, Albuquerque, NM 87123-3917. [c] 2005 by American Society of Radiologic Technologists.
Table 1 Classification Systems For Aortic Dissections DeBakey System Type I: Both ascending and descending aorta involvement Type II: Ascending aorta involvement only Type III: Descending aorta involvement only Stanford Classification Type A: Ascending aorta involvement (regardless of overall extent) Type B: Dissection limited to aorta distal to left subclavian artery Table 2 Causes and Risk Factors of Aortic Aneurysms Atherosclerosis Cystic medial necrosis * Marfan syndrome * Ehlers-Danlos syndrome * Primary Vasculitis * Rheumatoid arthritis * Takayasu syndrome * Giant cell arteritis * Ankylosing spondylitis * Reiter syndrome * Relapsing polychondritis Infection (infectious aortitis) * Syphilis * Tuberculosis * Mycotic staphylococcus * Mycotic streptococcus * Mycotic salmonella * Mycotic pseudomonas Congenital disorders Trauma
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