**5.3 Chest radiography**

**Widening of mediastinum** is the classic finding (approximately 60% of cases), but it may not reveal any abnormality. In any case it should not delay the performance of further imaging as CT or MRI [16]. A tortuous aorta (common in hypertensive patients) may be mistaken for widened mediastinum; other differential diagnoses for widened mediastinum include enlarged thyroid, lymphoma, tumors, and adenopathy [17].

Hemothorax is expected to be seen as blood can accumulate in pleural space following dissection rupture.

Ring sign (aortic displacement more than 5 mm past the calcific aortic intima) and abnormal aortic contour can be seen in some patients.

Other radiological abnormalities can be seen including esophageal deviation, tracheal deviation to the right, depression of left mediastinal bronchus, left apical cap, pleural effusion, and loss of paratracheal stripe.

## **5.4 Echocardiography**

Transesophageal echocardiography has higher diagnostic index (sensitivity 99% and specificity 97%) than transthoracic echocardiography (sensitivity 80% and specificity 90%) [18].

**TEE is as accurate as CT and MRI,** and it can be used at bedside which makes it suitable for hemodynamically unstable patients.

Limitations of transesophageal echocardiography:


### **5.5 Computed tomography**

CT with contrast is used more frequently in emergency department settings, only on hemodynamically stable patients who do not have adverse reaction to the intravenous contrast agents.

A 2014 guideline form American College of Radiology recommends CT angiography as the definite modality if there is high clinical suspicion for aortic dissection [16].

**71**

*Aortic Dissection*

plaque formation.

Limitations of CT:

material.

lumen [21].

dissection.

*DOI: http://dx.doi.org/10.5772/intechopen.89210*

CTA provides detailed anatomic definition of the dissection and information about

• Cannot provide information about aortic regurgitation.

**5.6 Smooth-muscle myosin heavy-chain assay**

**5.8 Magnetic resonance imaging (MRI)**

impairment or allergic to iodine [22].

• Requires much more time than CT.

aortic regurgitation, and coronary arteries.

Limits of aortography:

• Invasive procedure.

Limitations of MRI:

**5.9 Aortography**

Spiral (helical) CT is associated with higher rate of detection and better resolution than incremental CT scanning. Imaging information, including type of the lesion, location of 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 [16, 20].

• CTA not suitable for patient with renal impairment or allergy to contrast

Performed in the first 24 hours. **Levels are higher in the first 3 hours**; a 2.5-fold

Plasma fibrin degradation product level (FDP) of **12.6 μg/mL or higher** is suggestive of the possibility of aortic dissection with false lumen in symptomatic patient. Plasma fibrin degradation product level (FDP) of 5.6 μg/mL or higher is suggestive of the possibility of dissection with complete thrombosis of the false

increase has a sensitivity of 91% and specificity of 98% for aortic dissection.

MRI has 98% sensitivity and specificity in detection of thoracic aortic

• Not suitable for hemodynamically unstable patients.

*5.9.1 The gold-standard diagnostic modality for aortic dissection*

MRI shows the site on intimal tear, type and extent of dissection, presence of aortic insufficiency, as well as surrounding mediastinal structures. It has the advantage of not using contrast material; thus, it is preferred in patients with renal

• Not suitable for patients with pacemaker and other metallic implants [23].

Benefits include accurate visualization of the true and false lumen, intimal flap,

**5.7 Measurement of the degradation products of plasma fibrin and fibrinogen**

• Hemodynamic unstable patients cannot be shifted to radiology department.

CTA provides detailed anatomic definition of the dissection and information about plaque formation.

Spiral (helical) CT is associated with higher rate of detection and better resolution than incremental CT scanning. Imaging information, including type of the lesion, location of 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 [16, 20].

Limitations of CT:

*Differential Diagnosis of Chest Pain*

**dimer is negative** [15].

**5.3 Chest radiography**

and adenopathy [17].

**5.4 Echocardiography**

specificity 90%) [18].

• Operator dependent.

• Difficulty in obese patients.

decrease its accuracy.

aorta [19].

**5.5 Computed tomography**

intravenous contrast agents.

following dissection rupture.

arteries and caused myocardial ischemia.

**Troponin I and T may be elevated** if the dissection has involved the coronary

LDH (lactate dehydrogenase) may be elevated due to hemolysis in the false lumen. D dimer: high negative predictive value. **Aortic dissection is less likely if D** 

**Widening of mediastinum** is the classic finding (approximately 60% of cases), but it may not reveal any abnormality. In any case it should not delay the performance of further imaging as CT or MRI [16]. A tortuous aorta (common in hypertensive patients) may be mistaken for widened mediastinum; other differential diagnoses for widened mediastinum include enlarged thyroid, lymphoma, tumors,

Hemothorax is expected to be seen as blood can accumulate in pleural space

and abnormal aortic contour can be seen in some patients.

cap, pleural effusion, and loss of paratracheal stripe.

suitable for hemodynamically unstable patients.

Limitations of transesophageal echocardiography:

• Not suitable for patients with esophageal stenosis or varicosities.

• Upper ascending aorta and arch may not be evaluated well.

Ring sign (aortic displacement more than 5 mm past the calcific aortic intima)

Other radiological abnormalities can be seen including esophageal deviation, tracheal deviation to the right, depression of left mediastinal bronchus, left apical

Transesophageal echocardiography has higher diagnostic index (sensitivity 99% and specificity 97%) than transthoracic echocardiography (sensitivity 80% and

**TEE is as accurate as CT and MRI,** and it can be used at bedside which makes it

• Narrow intercostal space, pulmonary emphysema, and mechanical ventilation

• False-positive results may occur due to reverberations in the ascending

CT with contrast is used more frequently in emergency department settings, only on hemodynamically stable patients who do not have adverse reaction to the

A 2014 guideline form American College of Radiology recommends CT angiography as the definite modality if there is high clinical suspicion for aortic dissection [16].

**70**

