Aortic Dissection

3:1 male to female predominance Over the age of 40 Hemorrhage in the media leading to either Tear in the weakened intima which breaks into the lumen, or Hemorrhage in the wall (less common) Hemorrhage separate media from adventitia

Predisposing factors Hypertension (most commonly) Atherosclerosis Marfan’s syndrome Coarctation of the aorta Trauma (rare) Pregnancy (rare)

Aneurysm defined by size criteria In general, ascending aorta > 5 cm Descending aorta > 4 cm 

Vessels involved with dissection Any artery can be occluded Usually the right coronary and three arch vessels are involved with arch aneurysms Right pulmonary artery and left-sided pulmonary veins may be occluded

Types DeBakey Type I DeBakey Type II DeBakey Type III Stanford Type A Involves entire aorta DeBakey Type II Least common Ascending aorta only DeBakey Type III Most common Descending aorta only Stanford Type A Ascending aorta involved Over half develop aortic regurgitation（返流） Stanford Type B Ascending aorta NOT involved

True versus false channel Most dissections arise either just distal to the aortic valve or just distal to aortic isthmus True versus false channel False channel usually arises anterior in the ascending aorta and spirals to posterior and left lateral in descending aorta True channel is usually larger Slower flow in false channel on MR

DeBakey Classification Stanford Classification Portion of Aorta Involved Common causes RX DeBakey Type I   Stanford Type A (ascending aorta involved) Involves entire aorta  Hypertension Atherosclerosis Usually surgically* DeBakey Type II (least common)  Stanford Type A (ascending aorta involved)  Ascending aorta only  Cystic medial necrosis e.g.Marfan’s DeBakey Type III (most common)  Stanford Type B Descending aorta only  Hypertension Atherosclerosis Usually medically *Goal is to prevent backward involvement of the aortic valve or rupture into pericardium

Clinical Sharp, tearing, intractable chest pain Previously hypertensive, now possible shock Asymmetric peripheral pulses Pulmonary edema

Imaging Findings Chest films Mediastinal widening Left paraspinal stripe Displacement of intimal calcifications Left pleural effusion Displacement of endotracheal tube or nasogastric tube

MRI CT Intimal flap Slow flow or clot in false lumen Displacement of intimal calcification Differential contrast enhancement of true versus false lumen 

The roles of CT in the evaluation of suspected aortic dissection are: Computed tomography of the chest including CTA of the aorta is the investigation of choice for suspected aortic dissection. The roles of CT in the evaluation of suspected aortic dissection are: To confirm the diagnosis Classify the dissection as type A or B Identify involvement of arterial branches,including the coronary arteries Delineation of bleeding:mediastinal haematoma,pleural or pericardial（心包） effusion

CT of abdominal aorta show intimal flap (dark line) with true lumen anteriorly and false lumen posteriorly

Angiography Intimal flap Double lumen Compression of true lumen by false channel Increase in aortic wall thickness > 10 mm Obstruction of branch vessels 

Diagnosis MRI if available is usually best for imaging ascending aorta Contrast-enhanced CT can image arch and descending aorta Transesophageal ultrasound, if available, especially for root and ascending aorta Angiography