eMedicine Specialties > Emergency Medicine > Cardiovascular
Dissection, Aortic: Differential Diagnoses & Workup
Updated: Aug 28, 2009
- Overview
- Differential Diagnoses & Workup
- Treatment & Medication
- Follow-up
- Multimedia
Differential Diagnoses
Other Problems to Be Considered
Musculoskeletal chest pain
Workup
Laboratory Studies
- Blood studies
- Usually, the diagnosis is made before the blood work is returned; however, leukocytosis may be present.
- BUN and creatinine are elevated if the dissection involves the renal arteries.
- Troponin and creatine kinase (CK) can be elevated if the dissection has caused myocardial ischemia.
- Decreases in the hemoglobin and hematocrit are ominous findings suggesting the dissection either is leaking or has ruptured.
- Some studies suggest that D-dimer should be a part of the initial workup if aortic dissection is suspected. A negative result makes the presence of the disease unlikely.
- Hematuria, oliguria, and even anuria (<50 mL/d) may occur if the dissection involves the renal arteries.
Imaging Studies
- Chest radiography: Findings are abnormal in 80% of patients and are more commonly abnormal in ascending aortic dissections (see Media file 1).
Chest radiograph of a patient with aortic dissection. Image courtesy of Dr. K. London, University of California at Davis Medical Center.
- Findings suggesting hemothorax may be found if the dissection ruptures into the pleura (see Media file 2).
Chest radiograph of a patient with aortic dissection presenting with hemothorax.
- Radiographic findings in acute thoracic dissection include a widened mediastinum in many cases (see Media file 3).
Chest radiograph demonstrating widened mediastinum in a patient with aortic dissection.
- In 2000, the International Registry of Acute Aortic Dissection published data on 464 patients that showed only 25% presenting with this finding.6
- A widened mediastinum is sometimes difficult to identify on a portable anteroposterior (AP) radiograph. If the patient is hemodynamically stable and cooperative, an AP radiograph can be obtained at bedside.
- Look for a mediastinal width greater than 8 cm on AP chest radiograph.
- A tortuous aorta, common in hypertensive patients, may be hard to distinguish from a widened mediastinum. If in doubt, a good posterior-anterior radiograph is recommended.
- The differential diagnosis of a widened mediastinum includes tumor, adenopathy, lymphoma, and enlarged thyroid.
- Abnormal (ie, blunted) aortic knob was observed in 66% of patients in one study.
- Ring sign (displacement of the aorta >5 mm past the calcified aortic intima) is considered a specific radiographic sign.
- Other radiologic abnormalities seen on chest radiography include the following:
- Left apical cap
- Tracheal deviation
- Depression of left main stem bronchus
- Esophageal deviation
- Loss of the paratracheal stripe
- The International Registry for Aortic Dissection revealed that over 12% of the chest radiographs of patients with aortic dissection were read as normal.6 Several studies concluded that the overall diagnosis of aortic dissection is not determined by any one sign, rather a combination of all findings leads to suspicion of dissection.
- Angiography: Still considered by some as the diagnostic criterion standard test for aortic dissection, it is being replaced by newer imaging modalities.
- Angiography leads to accurate diagnosis of aortic dissection in over 95% of patients (see Media file 4) and aids the surgeon in planning the repair operation because blood vessels of the arch can be assessed easily. Benefits include visualization of the true and false lumens, intimal flap, aortic regurgitation, and coronary arteries.
Angiogram demonstrating dissection of the aorta (same patient as in Image 3).
- Drawbacks include the following:
- The procedure is invasive.
- The patient must be transported to the radiology department, leaving the ED.
- The use of contrast media may be harmful to patients who have renal insufficiency or an allergy to iodine.
- Misdiagnoses can occur if the false channel is thrombosed. In this instance, the false lumen and intimal flap may not be visualized. Possible simultaneous opacification of the true and false lumens may make discerning the presence of a dissection difficult.
- Computed tomography (CT) scanning: The accepted diagnostic criterion standard, angiography, is being challenged by state-of-the-art CT angiography. With the advent of helical CT with multiplanar and 3D reconstruction and CT angiography, CT scanning is quickly replacing angiography as the diagnostic test of choice in many institutions.
Patient with a type A aortic dissection involving the ascending and descending aorta. Image courtesy of Kaiser-Permanente.
Patient showing a type B aortic dissection with extravasation of blood into the pleural cavity. Image courtesy of Kaiser-Permanente.
- Prospective studies have shown a sensitivity of 83-94% with a specificity of 87-100%.
- Spiral CT scanning is associated with a higher rate of detection and better resolution than incremental CT scanning. High-quality 2D and 3D reconstructions are possible with spiral CT scanning, which greatly adds to the usefulness of this imaging modality.
- More importantly, imaging information, including the type of lesion, location of the pathologic lesion, extent of the disease, and evaluation of the true and false lumen can be assessed quickly and help the surgeon plan the operation.
- This information helps determine if hypothermic circulatory arrest is necessary for surgery; this procedure increases the complexity, length, morbidity, and mortality associated with surgery.
- Faster scanners have decreased the acquisition time to the range of a breath hold, resulting in less motion artifact from breathing.
- Drawbacks include the following:
- Transportation of a patient in potentially unstable condition from the ED, even for the relatively short time needed for this procedure, places the patient at risk.
- CT angiography requires the injection of iodinated contrast.
- The use of contrast material may harm a patient who has impaired renal function or an allergy to contrast media.
- CT scanning provides no information on aortic regurgitation.
- Echocardiography
- With its increasing acceptance and use in the ED, ultrasonography is becoming a valuable diagnostic aid, although transthoracic echocardiography (TTE) has a much lower sensitivity (80%) and lower specificity (90%) than angiography.
- TTE is most useful in ascending aortic dissections, especially those closest to the aortic root and within a few centimeters of the aortic valve. Sensitivity is highest in this location.
- Echocardiography also is useful in diagnosing cardiac tamponade and aortic regurgitation.
- Benefits include its rapid simple bedside use in the ED and its noninvasive nature.
- Drawbacks include the lack of sensitivity and specificity, especially with arch and descending aortic dissections, and dependence on operator experience.
- Transesophageal echocardiography (TEE) has greater sensitivity and specificity than TTE (in the range of 97-99% and 97-100%, respectively).
- Advantages include its quick and easy bedside use in the ED, which makes it ideal for patients in unstable condition.
- TEE detects involvement of the coronary arteries, aortic insufficiency, and cardiac tamponade.
- It is a relatively quick study to perform and relatively noninvasive.
- The main drawback of TEE is its strong dependence on operator experience.
- Other drawbacks are that false-positive results can occur from reverberations in the ascending aorta and that the upper ascending aorta and arch may not be visualized well, leading to false-negative results.
- TEE cannot be performed in patients with esophageal varicosities or stenosis. If the findings are negative and clinical suspicion remains high, a second diagnostic test is recommended.
- Magnetic resonance imaging (MRI)
- MRI has over 90% sensitivity and greater than 95% specificity. It is the most sensitive method for diagnosing aortic dissection and has similar specificity to CT scanning.
- MRI shows the site of intimal tear, type and extent of dissection, and presence of aortic insufficiency, as well as the surrounding mediastinal structures.
- Other benefits are that MRI requires no contrast medium and no ionizing radiation. It is the preferred modality for patients with renal failure and those with an allergy to iodine.
- Contrast-enhanced magnetic resonance angiography (CE-MRA) is a principle technique for evaluating the thoracic aorta.
- MRI is the preferred tool for imaging chronic dissections and postsurgical follow-up.
- Contrast 3D MRA is an accurate noninvasive imaging modality. It has the advantage of being able to evaluate the aortic valve more effectively than CT angiography.
- Drawbacks include the following:
- MRI is not readily available at most institutions, requiring transportation of patients in unstable condition away from the ED.
- MRI requires much more time to acquire images than CT scanning.
- Patients with permanent pacemakers cannot undergo MRI. Most patients with prosthetic heart valves or coronary stents can safely have an MRI.
Other Tests
- ECG: All patients with suspected thoracic aortic dissection should have an ECG.
- In acute thoracic dissection, ECG can mimic the changes seen in acute cardiac ischemia. In the presence of chest pain, these signs can make distinguishing dissection from AMI very difficult (see Media file 5). Keep this in mind when administering thrombolytics to patients with chest pain.
Electrocardiogram of a patient presenting to the ED with chest pain; this patient was diagnosed with aortic dissection.
- ST elevation can be seen in Stanford type A dissections because the dissection interrupts blood flow to the coronary arteries.
- The incidence of abnormal ECG findings is greater in Stanford type A dissections than in other types of dissections.
- In one study, 8% of patients with type A dissections had ST elevation, while no patients with type B dissections had ST elevation.
- More commonly, the ECG abnormality is ST depression.
- If the dissection involves the coronary ostia, it is the right coronary artery that is most commonly involved, leading to inferior ST-segment elevation pattern.
More on Dissection, Aortic |
| Overview: Dissection, Aortic |
 Differential Diagnoses & Workup: Dissection, Aortic |
| Treatment & Medication: Dissection, Aortic |
| Follow-up: Dissection, Aortic |
| Multimedia: Dissection, Aortic |
| References |
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Further Reading
Keywords
aortic dissection, thoracic aortic dissection, dissection of the thoracic aorta, aortic aneurysm, aortic tear, tear in the aortic wall, Stanford classification, DeBakey classification, cystic medial necrosis, atherosclerosis, Marfan syndrome, Ehlers-Danlos syndrome, adult polycystic kidney disease, Turner syndrome, Noonan syndrome, osteogenesis imperfecta, bicuspid aortic valve, coarctation of the aorta, connective-tissue disorders, homocystinuria, familial hypercholesterolemia, syphilis, crackcocaine use, cardiac catheterization, myocardial infarction, syncope, cerebrovascular accident
