aortic dissection aortic dissection aortic dissection (ad) occurs when an injury to the innermost layer of the aorta allows blood to flow between the layers of the aortic wall, forcing the layers apart. in most cases, this is associated with a sudden onset of severe chest or back pain, often described as "tearing" in character. also, vomiting, sweating, and lightheadedness may occur. other symptoms may result from decreased blood supply to other organs, such as stroke, lower extremity ischemia, or mesenteric ischemia. aortic dissection can quickly lead to death from insufficient blood flow to the heart or complete rupture of the aorta. not to be confused with abdominal aortic aneurysm or aortic rupture. aortic dissectiondissection of the descending part of the aorta (3), which starts from the left subclavian artery and extends to the abdominal aorta (4). the ascending aorta (1) and aortic arch (2) are not involved in this image.specialtyvascular surgery, cardiothoracic surgerysymptomssevere chest or back pain, vomiting, sweating, lightheadednesscomplicationsstroke, mesenteric ischemia, myocardial ischemia, aortic ruptureusual onsetsuddenrisk factorshigh blood pressure, marfan syndrome, turner syndrome, bicuspid aortic valve, previous heart surgery, major trauma, smokingdiagnostic methodmedical imagingpreventionblood pressure control, not smoking treatmentdepends on the typeprognosismortality without treatment 10% (type b), 50% (type a)frequency3 per 100,000 per year ad is more common in those with a history of high blood pressure; a number of connective tissue diseases that affect blood vessel wall strength including marfan syndrome and ehlers–danlos syndrome; a bicuspid aortic valve; and previous heart surgery. major trauma, smoking, cocaine use, pregnancy, a thoracic aortic aneurysm, inflammation of arteries, and abnormal lipid levels are also associated with an increased risk. the diagnosis is suspected based on symptoms with medical imaging, such as ct scan, mri, or ultrasound used to confirm and further evaluate the dissection. the two main types are stanford type a, which involves the first part of the aorta, and type b, which does not. prevention is by blood pressure control and smoking cessation. management of ad depends on the part of the aorta involved. dissections that involve the first part of the aorta (adjacent to the heart) usually require surgery. surgery may be done either by an opening in the chest or from inside the blood vessel. dissections that involve the second part of the aorta can typically be treated with medications that lower blood pressure and heart rate, unless there are complications which then require surgical correction. ad is relatively rare, occurring at an estimated rate of three per 100,000 people per year. it is more common in men than women. the typical age at diagnosis is 63, with about 10% of cases occurring before the age of 40. without treatment, about half of people with stanford type a dissections die within three days and about 10% of people with stanford type b dissections die within one month. the first case of ad was described in the examination of king george ii of great britain following his death in 1760. surgery for ad was introduced in the 1950s by michael e. debakey. signs and symptoms about 96% of individuals with ad present with severe pain that had a sudden onset. the pain may be described as a tearing, stabbing, or sharp sensation in the chest, back, or abdomen. about 17% of individuals feel the pain migrate as the dissection extends down the aorta. the location of pain is associated with the location of the dissection. anterior chest pain is associated with dissections involving the ascending aorta, while interscapular back pain is associated with descending aortic dissections. if the pain is pleuritic in nature, it may suggest acute pericarditis caused by bleeding into the sac surrounding the heart. this is a particularly dangerous eventuality, suggesting that acute pericardial tamponade may be imminent. pericardial tamponade is the most common cause of death from ad. while the pain may be confused with that of a heart attack, ad is usually not associated with the other suggestive signs, such as heart failure and ecg changes. less common symptoms that may be seen in the setting of ad include congestive heart failure (7%), fainting (9%), stroke (6%), ischemic peripheral neuropathy, paraplegia, and cardiac arrest. if the individual fainted, about half the time it is due to bleeding into the pericardium, leading to pericardial tamponade. neurological complications of aortic dissection, such as stroke and paralysis, are due to the involvement of one or more arteries supplying portions of the central nervous system. if the ad involves the abdominal aorta, compromise of one or both renal arteries occurs in 5–8% of cases, while ischemia of the intestines occurs about 3% of the time. blood pressure people with ad often have a history of high blood pressure. the blood pressure is quite variable at presentation with acute ad. it tends to be higher in individuals with a distal dissection. in individuals with a proximal ad, 36% present with hypertension, while 25% present with hypotension. proximal ad tends to be associated with weakening of the vascular wall due to cystic medial degeneration. in those who present with distal (stanford type b) ad, 60–70% present with high blood pressure, while 2–3% present with low blood pressure. severe hypotension at presentation is a grave prognostic indicator. it is usually associated with pericardial tamponade, severe aortic insufficiency, or rupture of the aorta. accurate measurement of blood pressure is important. pseudohypotension (falsely low blood-pressure measurement) may occur due to involvement of the brachiocephalic artery (supplying the right arm) or the left subclavian artery (supplying the left arm). aortic insufficiency aortic insufficiency (ai) occurs in half to two-thirds of ascending ad, and the diastolic heart murmur of aortic insufficiency is audible in about 32% of proximal dissections. the intensity (loudness) of the murmur depends on the blood pressure and may be inaudible in the event of low blood pressure. multiple causes exist for ai in the setting of ascending ad. the dissection may dilate the annulus of the aortic valve, preventing the leaflets of the valve from coapting. the dissection may extend into the aortic root and detach the aortic valve leaflets. alternatively, following an extensive intimal tear, the intimal flap may prolapse into the left ventricular outflow tract, causing intimal intussusception into the aortic valve, thereby preventing proper valve closure. myocardial infarction heart attack occurs in 1–2% of aortic dissections. infarction is caused by the involvement of the coronary arteries, which supply the heart with oxygenated blood, in the dissection. the right coronary artery is involved more commonly than the left coronary artery. if the myocardial infarction is treated with thrombolytic therapy, the mortality increases to over 70%, mostly due to bleeding into the pericardial sac, causing cardiac tamponade. pleural effusion a pleural effusion (fluid collection in the space between the lungs and the chest wall or diaphragm) can be due to either blood from a transient rupture of the aorta or fluid due to an inflammatory reaction around the aorta. if a pleural effusion were to develop due to ad, it is more common in the left hemithorax rather than the right hemithorax. predisposing factors aortic dissection is associated with hypertension (high blood pressure) and many connective tissue disorders. vasculitis (inflammation of an artery) is rarely associated with aortic dissection. it can also be the result of chest trauma. about 72 to 80% of individuals who present with an aortic dissection have a previous history of hypertension. illicit drug use with stimulants such as cocaine and methamphetamine is also a modifiable risk factor for ad. it can also be caused by smoking. a bicuspid aortic valve (a type of congenital heart disease involving the aortic valve) is found in 7–14% of individuals who have an aortic dissection. these individuals are prone to dissection in the ascending aorta. the risk of dissection in individuals with bicuspid aortic valves is not associated with the degree of stenosis of the valve. connective tissue disorders such as marfan syndrome, ehlers–danlos syndrome, and loeys–dietz syndrome increase the risk of aortic dissection. similarly, vasculitides such as takayasu's arteritis, giant cell arteritis, polyarteritis nodosa, and behçet's disease have been associated with a subsequent aortic dissection. marfan syndrome is found in 5–9% of individuals who had an aortic dissection. in this subset, the incidence in young individuals is increased. individuals with marfan syndrome tend to have aneurysms of the aorta and are more prone to proximal dissections of the aorta. turner syndrome also increases the risk of aortic dissection, by aortic root dilatation. chest trauma leading to aortic dissection can be divided into two groups based on cause: blunt chest trauma (commonly seen in car accidents) and iatrogenic. iatrogenic causes include trauma during cardiac catheterization or due to an intra-aortic balloon pump. aortic dissection may be a late sequela of heart surgery. about 18% of individuals who present with an acute aortic dissection have a history of open-heart surgery. individuals who have undergone aortic valve replacement for aortic insufficiency are at particularly high risk because aortic regurgitation causes increased blood flow in the ascending aorta. this can cause dilatation and weakening of the walls of the ascending aorta. syphilis only potentially causes aortic dissection in its tertiary stage. pathophysiology blood penetrates the intima and enters the media layer. as with all other arteries, the aorta is made up of three layers, the intima, the media, and the adventitia. the intima is in direct contact with the blood inside the vessel, and mainly consists of a layer of endothelial cells on a basement membrane; the media contains connective and muscle tissue, and the vessel is protected on the outside by the adventitia, comprising connective tissue. in an aortic dissection, blood penetrates the intima and enters the media layer. the high pressure rips the tissue of the media apart along the laminated plane splitting the inner two-thirds and the outer one-third of the media apart. this can propagate along the length of the aorta for a variable distance forward or backward. dissections that propagate towards the iliac bifurcation (with the flow of blood) are called anterograde dissections and those that propagate towards the aortic root (opposite of the flow of blood) are called retrograde dissections. the initial tear is usually within 100 mm of the aortic valve, so a retrograde dissection can easily compromise the pericardium leading to a hemopericardium. anterograde dissections may propagate all the way to the iliac bifurcation of the aorta, rupture the aortic wall, or recanalize into the intravascular lumen leading to a double-barrel aorta. the double-barrel aorta relieves the pressure of blood flow and reduces the risk of rupture. rupture leads to hemorrhaging into a body cavity, and prognosis depends on the area of rupture. retroperitoneal and pericardial ruptures are both possible. histopathological image of dissecting aneurysm of the thoracic aorta in a patient without evidence of marfan syndrome: the damaged aorta was surgically removed and replaced by artificial vessel, victoria blue and he stain. the initiating event in aortic dissection is a tear in the intimal lining of the aorta. due to the high pressures in the aorta, blood enters the media at the point of the tear. the force of the blood entering the media causes the tear to extend. it may extend proximally (closer to the heart) or distally (away from the heart) or both. the blood travels through the media, creating a false lumen (the true lumen is the normal conduit of blood in the aorta). separating the false lumen from the true lumen is a layer of intimal tissue known as the intimal flap. the vast majority of aortic dissections originate with an intimal tear in either the ascending aorta (65%), the aortic arch (10%), or just distal to the ligamentum arteriosum in the descending thoracic aorta (20%). as blood flows down the false lumen, it may cause secondary tears in the intima. through these secondary tears, the blood can re-enter the true lumen. while it is not always clear why an intimal tear may occur, quite often it involves degeneration of the collagen and elastin that make up the media. this is known as cystic medial necrosis and is most commonly associated with marfan syndrome and is also associated with ehlers-danlos syndrome. in about 13% of aortic dissections, no evidence of an intimal tear is found. in these cases, the inciting event is thought to be