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Diseases of the thoracic and abdominal aorta (aneurysm-dissection-aortic intramural hematoma / penetrating aortic ulcer)

Acute aortic dissection (type A), transesophageal echocardiographic 5 chamber midesophageal view. The image shows: The intimal flap inside the significantly dilated ascending aorta (Ao) Ao valve aortic valve, LV left ventricle, LA left atrium, RV right ventricle). Courtesy of Dr. Ioannis Dernellis cardiologist.)

Anatomy of the aorta

The aorta is the largest artery of the body and is divided into two parts: the thoracic and the abdominal aorta. The wall of the aorta consists of three layers: the intima, media, and adventitia. The intima is the inner layer, the media is the middle layer, and the adventitia is the outer layer.
The thoracic aorta arises from the left ventricle at the level of the third sternocostal joint and it consists of the ascending aorta, the aortic arch, and the descending thoracic aorta, which extends down to the diaphragm.
The ascending aorta extends from the aortic valve to the origin of the innominate (brachiocephalic) artery. The aortic root consists of the aortic annulus (the "ring" of the aortic valve) and the three sinuses of Valsalva (aortic sinuses) with the two coronary arteries originating from the left and right sinus. Normally, the widest portion of the aorta is at the sinuses of Valsalva. The aortic root ends at the sinotubular junction, which is the point where the tubular ascending aorta begins. The tubular ascending aorta is the distal part of the ascending aorta.
The aortic arch is defined as the segment of the aorta from which the large blood vessels of the head and upper limbs originate. It gives three branches, the innominate (brachiocephalic) artery, which divides into the right subclavian artery and the right common carotid artery, the left common carotid artery, and the left subclavian artery.
Immediately adjacent to the left subclavian artery is the arterial ligament (ligamentum arteriosum), in the place of the closed arterial duct (ductus arteriosus) that existed in fetal life. The aortic isthmus is a short segment of the aorta located between the left subclavian artery and the ligamentum arteriosum. The aortic isthmus is the most common site of the aorta where diseases occur. Such disorders and diseases are coarctation of the aorta, persistent ductus arteriosus, and aortic dissection of traumatic etiology, e.g., due to chest injury or injury to the aorta, such as the deceleration injury that occurs in traffic accidents.
The descending thoracic aorta begins just distal to the origin of the left subclavian artery and penetrates the diaphragm at the level of the 12th thoracic vertebra, where it continues down into the abdominal aorta. The descending thoracic aorta gives the following branches: the bronchial arteries, the esophageal arteries, and the third to twelfth intercostal arteries. (The first 2 intercostal arteries are branches of the subclavian arteries).
The abdominal aorta is smaller in diameter than the thoracic aorta. It begins from the aortic hiatus of the diaphragm and courses downward, giving branches that deliver blood to the abdominal viscera, and ends at the lower level of the 4th lumbar vertebra (L4) dividing into the two common iliac arteries. The iliac arteries supply with blood the pelvis and lower extremities. The abdominal aorta gives the following three groups of branches a) unpaired visceral arteries to the gastrointestinal tract,
spleen, pancreas, gallbladder, and liver b) paired arteries to the kidneys, adrenal glands, and gonads. c) parietal branches to the structures of the abdominal wall.

Thoracic aortic aneurysm
Definition: It is a segment of the thoracic aorta with an abnormally increased diameter which is > 1.5 times the expected mean normal diameter. (Thus for the ascending aorta, an aneurysm will have a diameter > 2.75 cm /m² of body surface area). True aneurysms have a wall that consists of all three layers of the arterial wall, whereas in pseudoaneurysms there is a rupture of the inner and middle layers, and the aneurysm is surrounded only by the outer layer of the arterial wall and sometimes by a clot.
The most common thoracic aortic aneurysms are those of the ascending aorta, followed by the aneurysms of the descending aorta. Aneurysms of the aortic arch are rare.
Morphologically, aneurysms are classified as:
♦ fusiform aneurysms (most commonly), in which there is a uniform dilation of the entire periphery of the vessel in its affected segment, and
♦ saccular aneurysms where the dilation involves only a portion of the periphery of the vessel. These aneurysms often contain thrombus due to the slow flow of blood in the area of the aneurysmal sac.

Pathogenesis of thoracic aortic aneurysms

Aneurysms are due to abnormal production or progressive degeneration of aortic wall structural proteins (collagen and elastin). The most common cause of ascending aortic aneurysms is cystic medial necrosis, a form of degeneration of the aortic media (the middle layer of the aortic wall), with a reduced content of collagen and elastin fibers. This lesion is observed in some hereditary syndromes such as Marfan syndrome, Ehlers-Danlos syndrome, osteogenesis imperfecta, and polycystic kidney disease.
Cystic degeneration of the middle layer of the aortic wall (media) is also present in the case of annuloaortic ectasia (more common in males). In annuloaortic ectasia, there is an aneurysm of the proximal ascending aorta which involves the aortic root and there is also accompanying aortic regurgitation. Other manifestations and features of a particular genetic syndrome are not present, although a defective gene is implicated.
The most usual cause for aneurysms of the aortic arch and descending aorta is atherosclerosis, which causes degenerative changes in the vascular wall. Risk factors are hypertension (a major cause of dilatation in any part of the aorta), smoking, hypercholesterolemia, diabetes mellitus and advanced age. Other causes of aortic aneurysms:
Poststenotic dilatation of the aorta (e.g. in aortic valve stenosis, or in the aortic segment which is located just distally from the position of aortic coarctation),
infectious etiology (microbial or mycotic aneurysms due to septic emboli in ischemic endocarditis),
in the context of autoimmune or rheumatic disease (Takayasu arteritis, giant cell arteritis, ankylosing spondylitis, systemic lupus erythematosus, rheumatoid arthritis, Adamantiadis-Behcet disease, Reiter syndrome).
Aneurysms of the aortic sinuses of Valsalva present a separate category and are congenital. These aneurysms most commonly involve the right sinus (70%), less frequently the noncoronary sinus (25%).

Clinical manifestations and diagnosis of thoracic aortic aneurysms.

Thoracic aortic aneurysms are most often asymptomatic, and the diagnosis is often made by the finding of a widened mediastinum on a chest X-ray. A shift of the trachea or the left main bronchus due to pressure from the aneurysm may also be present.
Some patients may have symptoms of adjacent organ pressure: Dyspnea, cough (due to pressure on the trachea), hoarseness (due to pressure on the left recurrent laryngeal nerve), dysphagia (pressure on the esophagus), chronic mild deep chest pain (when this pain becomes more intense there is a suspicion of impending rupture). Manifestations of congestive heart failure can occur in the case of severe aortic valve regurgitation (due to large ascending aortic aneurysm).
In some patients, the first manifestation is aneurysm rupture, presenting with acute thoracic pain, hemorrhagic shock with a sudden decrease in blood pressure and death. In the case of hemorrhage into the pericardium, due to the rupture of an aneurysm of the ascending aorta, cardiac tamponade occurs.
Diagnostic tests for thoracic aortic aneurysms are the following: echocardiography (transthoracic and transesophageal), chest CT scan with intravenous radiographic contrast, magnetic resonance imaging, and aortography.

Transthoracic echocardiogram left parasternal long-axis view (PLAX view) in a 38-year-old woman with Marfan syndrome. What is the pathological finding shown in this image?

Aneurysm of the aortic root at the level of the Valsalva sinuses, maximum diameter 4.7 cm (Ao aorta, AoV aortic valve, RVOT right ventricular outflow tract, LA left atrium, LV left ventricle)

Treatment of thoracic aortic aneurysms and indications for surgery:

Long-term administration of beta-blockers is indicated in patients with thoracic aortic aneurysms (this treatment may delay aneurysm progression). Treatment with additional antihypertensive medications is indicated in hypertensive patients (strict control of hypertension is important). Surgical treatment with prosthetic graft placement is indicated:
1) In patients with symptoms such as thoracic pain indicative of rupture or of threatened rupture of the aneurysm, if the symptoms are not explained by another cause
2) In patients with manifestations due to compression of adjacent organs such as the esophagus, trachea, or left main bronchus, or
3) In asymptomatic patients with an ascending aortic aneurysm with a maximum diameter > 5.5 cm or when there is evidence of a rapid increase in the aneurysm diameter (> 1 cm in one year).
The general diameter threshold of 5.5 cm for ascending aortic aneurysm surgery is also applicable to patients with a bicuspid aortic valve, whereas in Marfan syndrome the threshold is lower (5 cm). Patients with an ascending aortic aneurysm and a bicuspid aortic valve may receive surgical treatment at a lower aneurysm diameter of 5 cm if they also have an additional risk factor for dissection, such as a family history of aortic dissection, an increasing diameter of the aneurysm > 3 mm / year, coarctation of the aorta, or small body size. Arterial hypertension is also considered a risk factor if it has not been adequately controlled. An indication for surgery in the case of an ascending aortic aneurysm is the coexistence of severe aortic regurgitation.
In patients with Marfan syndrome, there is an indication for surgical correction when the ascending aortic aneurysm diameter is > 5 cm. Moreover, in patients with Marfan syndrome, the decision for surgery can be made at a smaller threshold of aortic diameter, (at 45 mm) if they have any additional risk factors, such as
- a family history of aortic dissection
-an increase in aneurysm diameter> 3mm / year (using the same imaging technique)
- severe aortic regurgitation or
- a desire for pregnancy (because pregnancy is associated with an increased risk for a rapid increase in diameter and for the occurrence of complications of the aneurysm). Patients with manifestations of a connective tissue disorder similar to Marfan syndrome who do not completely meet the criteria of Marfan syndrome should receive the same treatment for the aneurysm and with the same diameter thresholds as patients diagnosed with Marfan syndrome.
In patients with an aneurysm confined to the aortic arch, surgical treatment should be considered if the maximal diameter of the aortic arch ≥ 55 mm (a class IIa indication in the guidelines).
For aneurysms of the descending thoracic aorta when there is an indication of surgery (see below for the diameter threshold ) Thoracic Endo-Vascular Aortic Repair (TEVAR) should be considered since it is preferable to surgery if the anatomy is appropriate. When repair with a stent-graft (TEVAR) is technically feasible, then this treatment (class IIa indication based on the ESC guidelines) should be seriously considered for patients with an aneurysm of the descending aorta with a diameter ≥ 55 mm. (5,5 cm). Endovascular repair is performed by the introduction of the guidewire and the stent delivery system, through the common femoral or iliac artery (following surgical exposure of the artery). The stent delivery system is advanced by sliding over the guidewire. In this manner, the guidewire and intraluminal stent-graft system are advanced to the descending thoracic aorta. The system is introduced from the iliac artery when the diameter of the femoral artery is not sufficient to allow this artery to be used as the entry site. In patients with an aneurysm of the descending aorta, when TEVAR is not technically feasible, surgical treatment should be considered if the aneurysm diameter ≥ 6 cm. Surgical intervention at a smaller descending aortic diameter threshold (5.5 cm) should be considered in patients with Marfan syndrome. When intervention is indicated for an aneurysm of the descending thoracic aorta in cases of Marfan syndrome or other connective tissue disorders, surgery should be preferred instead of endovascular repair with a stent (TEVAR).

Dilatation of the ascending aorta and pregnancy

Women with a dilated aortic root or ascending aorta with a diameter > 4.5 cm are at increased risk during pregnancy for a progressive increase in diameter, dissection, or rupture of the aorta. This risk is present for all women with ascending aortic aneurysms but is even higher in women with Marfan syndrome. In Marfan syndrome, there is an increased risk in pregnancy at a lower limit of aortic diameter (when the ascending aorta > 4 cm in diameter).
The increased risk of complications of aneurysms in pregnancy is attributable to the increased stroke volume in pregnancy, but possibly also hormonal changes adversely affect pre-existing histological lesions of the aortic wall.
In patients with aortic root or ascending aortic dilation who desire pregnancy, surgery in the ascending aorta (replacement of the aortic root and ascending aorta with a graft) before pregnancy is recommended in the following cases:
1. In patients without a genetic syndrome that increases the risk for aortic dissection (see below) when the ascending aorta has a maximum diameter of ≥ 50 mm (5 cm).
2. In patients with Marfan syndrome or other high-risk genetic syndromes, such as Loeys-Dietz syndrome, Ehlers-Danlos syndrome, or Smad-3 gene mutation, when the ascending aorta is ≥45 mm.
Body surface area should probably be taken into account in women with small body size. An ascending aorta diameter index>2.7 cm / m² body surface area is associated with a high risk of dissection, therefore pre-pregnancy prophylactic surgery should be considered. Patients with aortic root or ascending aortic dilation are usually on treatment with beta-blockers to slow and limit the progression of aortic dilation. These medications should be continued during pregnancy.

Abdominal aortic aneurysm

The descending thoracic aorta passes through the aortic hiatus of the diaphragm and continues into the abdominal aorta. (The aortic hiatus is a hole in the diaphragm through which the aorta, the azygos vein, and the thoracic duct enter the abdomen). The abdominal aorta is located in the retroperitoneal space, descends in front of the spine (in close proximity to the spine), slightly to the left of the midline. The abdominal aorta from top to bottom supplies the following branches: The celiac artery or celiac axis, the superior mesenteric artery (which runs immediately above the left renal vein, which is a branch of the inferior vena cava), the renal arteries (right and left-renal artery), and the inferior mesenteric artery. The abdominal aorta, at the level of the fourth lumbar vertebra, divides into the right and left common iliac arteries.
The inferior vena cava (IVC) is located to the right of the aorta. On ultrasound, the IVC is easily distinguished from the aorta since it has a more ellipsoid (oval) shape in transverse section and also a thinner wall than the abdominal aorta, which has a more round shape.
An aneurysm is a focal dilatation of an artery with diameter increased by at least 50% of the normal diameter. The wall of this dilated portion of the artery contains all three layers of the arterial wall. (If the wall of the aneurysm does not consist of all three layers of the arterial wall then it is called a pseudoaneurysm).
The most common aneurysms of the aorta are the abdominal aortic aneurysms (frequency> 3% in people > 50 years of age), while the aneurysms of the thoracic aorta are less common. The most common thoracic aortic aneurysms are those of the ascending aorta followed by the aneurysms of the descending aorta. Aortic arch aneurysms are rare. In the abdominal aorta, an aneurysm is a part of the artery with diameter ≥ 3 cm. The normal diameter of the abdominal aorta is 1.5 - 2.5 cm. When the diameter is 2.6-2.9 cm, this is considered as a mild or marginal dilation of the artery. About 90% of abdominal aortic aneurysms lie below the level of the renal arteries.

Causes and pathogenesis of abdominal aortic aneurysms

There is a degeneration of the aortic media (the middle layer of the aortic wall), resulting in a decrease in wall strength and a slow progressive dilation of the vessel. The most common underlying cause is atherosclerosis. Rarer causes are arteritis, injury, hereditary diseases of the connective tissue that cause cystic degeneration of the media, and damage to the vascular wall at sites of previous surgical anastomosis.

Risk Factors:

Smoking (Smoking is the risk factor most strongly associated with abdominal aortic aneurysms),

Old age,

Hypertension,

Male gender (abdominal aortic aneurysms are more common in men than in women),

Family history (a family history is present in about 15-20% of patients, indicating a genetic predisposition) and

Chronic obstructive pulmonary disease (COPD).

Men > 65 years of age, smokers are at higher risk for an abdominal aortic aneurysm, and especially so if they also have peripheral arterial disease. It has also been observed that in patients with aneurysms of the popliteal artery, commonly an aneurysm of the abdominal aorta is also present.

Preventive screening with abdominal aortic ultrasound is recommended for men ≥ 65 years of age, especially if they have a history of smoking or hypertension.

Clinical findings and diagnosis of abdominal aortic aneurysms

Most abdominal aortic aneurysms are asymptomatic and diagnosed as an incidental finding in imaging tests of the abdomen, usually performed for another reason. When symptoms are present, this is often an indication of aneurysm expansion. In some cases, mild pain may be present in the back, abdomen, or groin area. Pain limited within the groin area is a manifestation that is due to the retroperitoneal expansion of the aneurysm, with pressure on the femoral nerve. Some patients may have a feeling of palpitations in the abdomen, a feeling of abdominal fullness, a feeling of fast satiety with meals, nausea, or manifestations of peripheral embolism in the toes. A sudden expansion of the aneurysm causes severe and constant pain in the lumbar area, abdomen, or groin. In some cases, renal colic is misdiagnosed.
In cases of rupture of the aneurysm, in addition to pain, the clinical manifestations of circulatory shock predominate, with hypotension, tachycardia, pallor or cyanosis, an altered mental status (e.g. confusion, disorientation), or syncope. In > 50% of cases of ruptured abdominal aortic aneurysm, the patient dies of circulatory shock before arriving at the hospital. However, there are cases where the only manifestation is sudden severe pain in the lumbar area or abdomen. This is the case when the retroperitoneal tissues contain the hematoma preventing a massive hemorrhage and resulting in a relatively localized retroperitoneal hematoma.
Rupture of an abdominal aortic aneurysm should be suspected in all patients over 50 with acute abdominal or back pain and hypotension, or a palpable pulsatile mass in the abdomen. (This the classic diagnostic triad presentation). The mass may be obscured in patients with a large abdominal circumference. An episode of syncope can be indicative of orthostatic hypotension. In such patients, an emergency Doppler ultrasound should be performed to confirm the diagnosis. The patient should be transferred to the nearest high-volume hospital where a vascular/endovascular surgical team is available.
Physical examination: In most (but not all) cases of a clinically significant abdominal aortic aneurysm, a palpable pulsatile abdominal mass is detected on physical examination. However, it is often difficult or impossible to detect a pulsatile abdominal mass in obese patients.

Diagnosis of abdominal aortic aneurysms-Imaging

Ultrasound is the most widely used imaging test, with very high sensitivity and specificity for aneurysms below the level of the renal artery. It may also detect the presence of blood in the peritoneal cavity in the event of aneurysm rupture. A complete examination of the abdominal aorta can sometimes be difficult in obese patients, or when a large amount of bowel gas is present. Usually, no special preparation is required for the patient who is lying supine with a pillow under the head. Sometimes we need to place the patient in a lateral decubitus position in order to move gas-containing bowel segments that prevent clear imaging. A low ultrasound frequency is used. The transverse image plane is initially obtained, i.e. a plane perpendicular to the longitudinal axis of the body, with the transducer 3-4 cm above the navel and the marker of the transducer pointing towards the patient's right side, perpendicular to the longitudinal axis of the body. Then, by slowly dragging the transducer upwards and downwards, the abdominal aorta is visualized along its entire length, from the level of the celiac and upper mesenteric artery down to its bifurcation into the two common iliac arteries. If an aneurysm is present, a dilation of the aorta in the affected area is identified.
The aorta is then visualized along its longitudinal axis at the sagittal plane (with the transducer placed on the midline of the abdomen, above the aorta and its marker pointing towards the head of the patient). In this way, it is possible to visualize the abdominal aorta throughout its length. (Note: A sagittal plane is one directed from the front to the back and divides the body into a left and a right part). The transducer is then positioned more laterally in the abdomen and the aorta is again visualized along its longitudinal axis, but at a coronal plane (see figure). (A coronal plane is one that divides the body into an anterior and posterior portion, i.e a plane parallel to the anterior surface of the body.] This view allows for the measurement of the lateral diameter of the aorta. The iliac arteries should also be examined, in a longitudinal and transverse view, to check for an iliac artery aneurysm, or to determine if an abdominal aortic aneurysm extends to the iliac arteries.

Transducer positions for abdominal aortic ultrasound. The abdominal aorta is depicted in the figure in red color whereas the inferior vena cava in blue.

1 transverse view, 2 saggital view, 3 frontal view, 4 position for examination of the proximal segment , 5 position for examination of the bifurcation of the abdominal aorta.

Other imaging tests for the diagnosis of abdominal aortic aneurysms

Other diagnostic methods that provide more detailed images and are not affected by obesity or the presence of gas in the bowel, are computed tomography (CT) and magnetic resonance imaging (MRI). These tests accurately depict the location of the aortic branches relative to the aneurysmal segment of the aorta. Such information is useful in the event of an invasive procedure.
CT with intravenous contrast provides excellent image quality, and it is especially superior to ultrasound in the visualization of an aneurysm located above the renal arteries. It also depicts the posterior peritoneum. It has the disadvantage of exposing the patient to ionizing radiation and the use of iodine contrast agent (which may cause deterioration of renal function, especially in patients with a degree of renal impairment). MRI does not have these two disadvantages.

A man 65 years old asymptomatic, smoker with a history of mild hypercholesterolemia (cholesterol 240, LDL 175). Physical examination: pulses 80 / min without arrhythmia, blood pressure 155/80 mmHg. This is an image from his abdominal ultrasound (Click on the image for a larger view). What is the proposed management ?

The answer:

An abdominal aortic aneurysm up to 3.8 cm in diameter is depicted. Management: Administration of antihypertensive medication and statin (The patient is considered to have a high cardiovascular risk because he has an arterial disorder. Therefore, a reasonable target should be for arterial pressure ≤ 130/80 and LDL <70 mg / dl). The inclusion of a beta-blocker in his antihypertensive regimen should be strongly considered because this drug-class has a favorable effect on reducing the rate of expansion of the aortic aneurysms. The patient should also be advised on smoking cessation. At this diameter, surgery or any interventional procedure is not indicated, but ultrasound monitoring of the abdominal aortic aneurysm is required annually (once every year). When the diameter of the aneurysm reaches 4 cm or more, then ultrasound monitoring is recommended every 6 months.

Interventional treatment of abdominal aortic aneurysm

In case of a ruptured aortic aneurysm, emergency surgery must be performed immediately.

Other indications for invasive (surgical or interventional) treatment of an abdominal aortic aneurysm :

Surgery is required if symptoms arise due to expansion of the aneurysm, compression of adjacent structures, or vascular complications.
In case of an asymptomatic abdominal aortic aneurysm when there is a rapid increase in diameter (> 1 cm / year), or when the maximum diameter of the aneurysm is ≥ 5.5 cm in men or ≥ 5.2 cm women, the patient should be referred to a vascular surgeon, because invasive treatment is indicated.
There are two methods of invasive treatment of an abdominal aortic aneurysm: 1) open surgery with an abdominal or posterior peritoneal access and 2) endovascular (interventional) treatment.

Follow-up of patients diagnosed with an abdominal aortic aneurysm

Patients with an abdominal aorta diameter < 3 cm require no further monitoring for the abdominal aorta, only cardiovascular risk factors should be addressed. Asymptomatic aneurysms of maximal diameter 3-4 cm, annual monitoring with ultrasound is required. An asymptomatic aneurysm of diameter 4-4.5 cm in requires examination with ultrasound every six months, and when the maximal diameter is > 4.5 cm the patient should also be followed by a vascular surgeon. If the diameter is ≥ 5.5 cm or larger, or if symptoms occur, there is an indication for surgical treatment.

The acute aortic syndromes

The term "acute aortic syndromes" refers to severe and potentially life-threatening disease of the aortic wall, which usually presents with severe pain of sudden onset, often described as "stabbing or tearing" and other acute manifestations, depending on the location of the lesion and associated complications. The location of the pain may be in the anterior thorax, the posterior thorax, or the lumbar region (waist) and the abdomen, depending on the location of the aortic disease. The acute aortic syndromes include three pathological conditions, the most important of which is aortic dissection. The other two less common and more localized pathological conditions (they usually involve a smaller area of the aorta than aortic dissection) are the aortic intramural hematoma (IMH) and the penetrating aortic ulcer (PAU). The presence of pain, which is usually intense and of sudden onset (most often in the chest or back), is a common feature of all the above types of acute aortic syndromes. Therefore, there is an overlap in their clinical picture.
An acute aortic syndrome is suspected in the event of such persistent sudden pain in a patient with a history of either hypertension or an aortic aneurysm. The usual differential diagnosis includes an acute coronary syndrome.
The most common and important risk factor for an acute aortic syndrome is moderate to severe hypertension. However, other risk factors associated with atherosclerotic arterial disease (e.g. smoking, age, chronic kidney disease) also play an important role, while an important but less common risk factor is the presence of an inherited, connective tissue disease associated with risk of aortic dissection.
The diagnosis of acute aortic syndromes is based on three imaging techniques: ultrasound (transthoracic or transesophageal echocardiography for the thoracic aorta, with the latter having greater sensitivity and specificity, or abdominal ultrasound for the abdominal aorta), computed tomography (CT) or magnetic resonance imaging (MRI).
The classification of the acute aortic syndromes and its importance for the choice of the appropriate therapeutic strategy:The acute aortic syndromes are classified into: Type A when the ascending aorta is involved. In type A the lesion of the aortic wall may be limited to a part of the ascending aorta or it may extend from the ascending aorta also to other parts of the aorta. Type A acute aortic syndromes have a higher risk of early (in-hospital) mortality and usually require prompt surgical treatment.Type B: When there is no involvement of the ascending aorta. The lesion may be located in the descending thoracic or abdominal aorta or in the aortic arch. In type B, initial treatment usually includes only conservative medical treatment (pain management, beta-blockers, prompt treatment of hypertension with appropriate medications). In the case of a complicated clinical course, invasive treatment is indicated, preferably endovascular repair with placement of an intravascular stent-graft. Surgical treatment can be performed when endovascular treatment is not technically feasible.
The topic of aortic dissection is discussed below, while the description of the other two acute aortic syndromes follows immediately after the aortic dissection chapter.

Aortic dissection

Aortic dissection is one of the most severe causes of acute thoracic pain. It is the entry of blood from a rupture in the intima (inner layer) of the aorta into the aortic wall, forming a false lumen. An aortic dissection is more common in people of age 50-70 years, but it can also occur in younger people with aortic disease due to a connective tissue disorder, such as Marfan syndrome. The ratio of men to women with aortic dissection is 2: 1.

The site where the blood enters the aortic wall (the intimal tear) is located, in order of frequency, in the ascending aorta in 65% of cases (the most frequent location), in the descending thoracic aorta in 20% (the second most frequent location), in the aortic arch (10%) and in the abdominal aorta in 5% of cases.

Classification of aortic dissection

Classification based on the location of aortic dissection
According to the Stanford Classification :

Type A: any dissection involving the ascending aorta. An acute type A aortic dissection requires prompt surgical treatment (it is a surgical emergency).
Type B: any dissection that does not include the ascending aorta. The treatment is conservative (medical) unless there are indications of complications or propagation of the dissection.
According to the Debakey Classification:

Type I: The intimal tear (the site of blood entry) is in the ascending aorta, but the dissection extends more distally than the ascending aorta, into the aortic arch or even more distally into the descending aorta.
Type II: The dissection is confined to the ascending aorta.
Type III: The site of blood entry is in the descending aorta, thus the dissection is confined in the descending aorta, distally to the origin of the left subclavian artery.
Classification based on time:
Acute aortic dissection: one that occurred less than 2 weeks ago.
Chronic aortic dissection: when more than 2 weeks have elapsed from the time of occurrence of the dissection.
This distinction is important because the mortality curve increases sharply within the first 2 weeks, whereas after this time interval the mortality is significantly lower.

Clinical manifestations of aortic dissection

The pain is sudden, usually intense, tearing (like a tear or a knife), and excruciating (high-intensity unrelenting pain with sudden onset and lasting for hours). Although the pain is usually severe, in rare cases it can be mild or absent (in about 10% of cases). Pain location: in the sternal area or in the back. The pain may often gradually extend to the abdomen or hip or to the neck, depending on the propagation of the dissection. There is no referred pain of the upper extremities (a feature present in some cases of acute myocardial infarction, which is another cause of acute chest discomfort, always to be considered in the differential diagnosis). The pain of acute aortic dissection has its highest intensity from the beginning, in contrast to the pain of acute myocardial infarction.
The location of pain may indicate the site of the dissection. Anterior thoracic pain suggests a dissection located in the ascending aorta, while pain in the central region of the back, between the scapulae, is suggestive of dissection involving the descending aorta and abdominal pain occurs when the dissection is extending into the abdominal aorta. Neck and jaw pain may occur with dissection extending into the aortic arch and involving its branch vessels, whereas flank pain may occur when the dissection extends to a renal artery.
Aortic dissection usually affects people who have some predisposing factors (hypertension, atherosclerosis, Marfan syndrome, pregnancy in women with pre-existing aortic root dilation).
In addition to the pain, which is the most common manifestation, other manifestations may also be present or even predominate in the clinical picture, depending on the location and the extent of the dissection and its associated complications. Such manifestations include symptoms and signs of acute heart failure (due to acute severe aortic regurgitation), hypotension, syncope, or even cardiac arrest (due to a rupture of the aorta into the pericardial space causing tamponade), stroke, paraplegia. The last two (neurologic) manifestations are due to an obstruction of arteries involved in the perfusion of the brain, or the spinal cord, respectively. Rarely (in 1–2% of proximal aortic dissections) an acute myocardial infarction occurs, resulting from the occlusion of a coronary artery (more commonly the right coronary artery is involved). The patient with acute aortic dissection may present with elevated, normal or low blood pressure. Many patients present findings similar to the manifestations of an internal hemorrhage: pallor, perspiration (sweating), tachycardia, a low blood pressure of a previously hypertensive patient, and a decrease in the values of the hematocrit and hemoglobin. In case of a proximal aortic dissection, cardiac auscultation may reveal a high pitched decrescendo early-diastolic murmur of aortic regurgitation.

As already mentioned, blood flow to arteries arising from the area of the dissection is often interrupted and this can result in weak or absent pulses of the arteries of an upper or lower limb or an unpalpable pulse of a carotid artery or in the development of stroke symptoms (eg hemiparesis or hemianesthesia), hematuria, oliguria or anuria resulting from an obstruction of the renal arteries.

Imaging tests and the diagnosis of aortic dissection

The chest X-ray often shows a widened mediastinum due to aortic dilation. In some cases a pleural effusion (hemothorax) is also present.
Echocardiography (transthoracic and transesophageal), with the latter being much more useful) displays important findings: The aorta is usually appears dilated. The most characteristic finding of an aortic dissection is the intimal flap, a linear structure with a pulsatile motion in the aorta, which separates two spaces filled with blood, the two lumens:

a) The false lumen consists of blood which has entered the aortic wall. It often demonstrates slower blood flow (an appearance of spontaneous contrast which resembles "smoke" may be present in the false lumen) or occasionally a blood clot may form in the false lumen

b) The true lumen, i.e, blood that flows inside the aorta.

The true lumen is distinguished from the false by the different flow characteristics. The true lumen appears with color Doppler examination to fill with blood that flows with a higher velocity in systole than the blood velocity in the false lumen. In the false lumen, varying flow at slower velocities is demonstrated and/or areas with partial or complete thrombosis.

The point of entry of blood from the true lumen into the false lumen (the site of the intimal tear) may appear as a small area of turbulent flow with color Doppler examination. The false lumen is usually larger than the true lumen in diastole, whereas the true lumen expands during the phase of cardiac systole. The intimal flap in systole usually moves toward the false lumen. The one-dimensional M-mode echocardiography can be used to demonstrate more clearly the motion of the intimal flap: The intimal flap moves in the opposite direction than the aortic wall during the cardiac cycle. .
Transesophageal echocardiography (TEE) has the advantage of excellent sensitivity and specificity for the diagnosis of a dissection of the thoracic aorta, whereas transthoracic echocardiography is less sensitive and less specific than TEE.
Other imaging tests which can clearly depict with excellent sensitivity and specificity the false and the true lumen and the intimal flap, thus making the diagnosis of aortic dissection are the following: 1) Computed tomography with intravenous contrast (which is the imaging modality most often used for the diagnosis of aortic dissection) It is usually the modality of choice for hemodynamically stable patients, but TEE is usually preferred for unstable patients. 2) Magnetic resonance imaging (MRI), 3) Aortography (although previously considered as the gold standard, currently it has been largely replaced by the newer noninvasive imaging techniques).

Note: D-dimers (which are degradation products of plasma fibrin and fibrinogen) can also be considered as a useful but nonspecific test. This blood test can be a part of the initial workup when aortic dissection is suspected, because a negative result makes the presence of aortic dissection less likely.

Video: The following video is an overview of acute aortic dissection with a presentation of cases and findings on imaging tests ( transesophageal echocardiography, transthoracic echocardiography, chest X-ray, CT scan of the aorta, magnetic resonance imaging-MRI). After the case presentation, a summary of the etiology, diagnosis, and treatment of aortic dissection follows. I would like to thank my colleagues Ioannis Dernellis and Lambros Lakkas who have contributed images for this video. If you want to view the video in a large size, after you start it, you can click on the [] symbol at the bottom right of the video. (whereas you can return to a small size by pressing the esc key).

Prognosis

In acute type A aortic dissection, without treatment mortality in the first 48 hours is 1% per hour. In general, death in aortic dissection is due to (a) cardiac tamponade from hemorrhage into the pericardium. (b) aortic rupture, or (c) propagation of the dissection, leading to occlusion of arterial branches of the aorta. The prognosis can be improved by prompt and appropriate treatment.

Treatment of aortic dissection:

In acute type A dissection: Surgery is required promptly. In acute type B dissection, if the patient is stable, with no complications or evidence of propagation of the dissection, only conservative (medical) treatment is provided.
In a chronic dissection if the patient is stable, without complications and without signs of propagation, conservative treatment is also administered.
Conservative (drug) treatment is also provided to patients who have an indication for surgery, as the initial treatment until they are transferred to the operating room as soon as possible, and it is also administered as the only treatment to patients who have no indication for surgery.
The goal of drug therapy is to avoid propagation of the dissection, by reducing contractility of the left ventricle (so that it does not propel blood with a great force into the aorta), as well as by controlling blood pressure, if hypertension is present. In cases with hypertension, systolic pressure should be reduced to 100–120 mmHg. Analgesic treatment (morphine sulfate intravenously) is also given. In acute aortic dissection, a beta-blocker is initially administered intravenously, whereas in chronic aortic dissection a beta-blocker is administered orally. Α beta-blocker is administered not only when blood pressure is elevated, but also when it is normal. The reason is that beta-adrenergic receptor blockade reduces myocardial contractility, thereby reducing the rate of pressure rise (dP / dt) within the aorta. This action limits the expansion of the dissection, provided that there is no significant contraindication to the administration of a beta-blocker. The dose of the beta-blocker should be adjusted so that the heart rate is maintained at approximately 60-65 beats/ min. If blood pressure remains elevated after the administration of a beta-blocker, a vasodilator drug is added. In acute dissection of the aorta with a blood pressure above the desired target, the vasodilator drug sodium nitroprusside is administered intravenously.
To patients with acute heart failure due to acute aortic valve regurgitation (caused by the dissection), drugs that reduce contractility (such as beta-blockers) are not administered. In this case, only vasodilators (sodium nitroprusside) are indicated for the treatment of hypertension. In chronic aortic dissection, other antihypertensive drugs, such as an ACE-inhibitor, or a calcium channel antagonist are added to the treatment with a beta-blocker, when needed to control blood pressure. In patients with an aortic dissection, the arterial blood pressure must be strictly controlled.

Drug dosages:

Beta-blockers:
Atenolol 5–10 mg in slow intravenous injection. After 15 minutes 50 mg orally (PO) , after 12 hours 25-50 mg PO and then treatment is continued with 50-100 mg PO daily. Alternatively:
Propanolol intravenously 0.5-1 mg every 2–5 min until heart rate is reduced to 60-70 beats/ min (maximal dose 10 mg). Then usually 1 mg every 3-6 hours is administered intravenously. When oral medication is started, the dose is 10–40 mg PO x 3–4 times/day.

Sodium Nitroprusside: It is administered by intravenous infusion of 0.25–10 µg / kg body weight / min.

(mg = milligram / μg = microgram).

Other acute aortic syndromes

Patients with these syndromes (aortic intramural haematoma and penetrating aortic ulcer) have the same risk factors and several similarities in the clinical picture with patients with acute aortic dissection. However, these patients tend to be older (regarding their mean age) compared to those with aortic dissection. While the pain occurring in these two acute aortic syndromes is similar to the pain of acute aortic dissection, clinical manifestations of arterial occlusion are less common, because these syndromes are typically characterized by a more localized aortic lesion.

Aortic intramural hematoma

Aortic intramural hematoma is characterized by the presence of blood inside the aortic media (the middle layer of the aortic wall). This is thrombosed blood without flow. Imaging techniques do not demonstrate a visible site of rupture of the inner layer of the aortic wall (intimal tear) in contrast to aortic dissection. Also in contrast to aortic dissection, there is no intimal flap and one or more sites of return of blood from the aortic wall back to the true aortic lumen are not present. Pain may occur due to the dilatation of the outer layer (adventitia) of the aortic wall.
Intramural hematoma (IMH) is etiologically attributed to:
-Rupture of vessels of the aortic wall (small arteries that supply blood to the aortic wall- vasa vasorum) or

-In a few patients, an intimal tear may be present, which is not detectable, due to its small size, with blood entering the aortic wall and subsequent thrombosis of this intramural blood.

A CT angiography of the aorta depicts a thickening of the aortic wall with a crescentic shape and relatively high density. It is not enhanced by the contrast medium and involves a short or long segment of the aorta. On magnetic resonance imaging (MRI) the intramural hematoma in the acute phase (within the first 24-72 hours) in the T1 sequences appears as a crescentic (semilunar) or circular thickening of the arterial wall of approximately the same density (signal strength) as the aortic wall, while in T2 sequences it is depicted as a signal of increased intensity (white). After the first 24-72 hours, it appears as a signal of increased intensity within the wall also in T1 sequences due to the change in hemoglobin from oxyhemoglobin to meta-hemoglobin.

Aortic CT angiography: What do the arrows show?

1. intramural hematoma in the ascending aorta 2. intramural hematoma in the descending thoracic aorta 3. sternum, 4. ascending aortic lumen (shown white due to the intravenous contrast), 5. right pulmonary artery, 6. left atrium, 7.body of thoracic vertebra, 8. right lung, 9. left lung, 10. lumen of the descending thoracic aorta

A penetrating aortic ulcer (PAU) is an erosion of an atherosclerotic plaque that penetrates the inner layer of the aortic wall (intima) and reaches deeper into the middle layer (media). It is often accompanied by the formation of an intramural hematoma. Often aortic ulcers can be multiple and their depth may vary from 4 to 30 mm. Typical patients are elderly (> 70 years) and often have diffuse and extensive atherosclerotic disease of both the aorta and the coronary arteries. In transesophageal echocardiography, a penetrating ulcer of the aorta is imaged as a focal outpouching of the aortic lumen, which resembles a crater entering into the vessel wall. This is located at the site of an atherosclerotic plaque. Color Doppler shows that blood enters this crater. It can often be accompanied by an intramural hematoma.

MRI also shows a penetrating ulcer of the aorta as a crater-like wall lesion that penetrates into the media. Magnetic angiography (MRI with intravenous administration of contrast) shows that the lumen of the artery forms in that position an outpouching that enters the vascular wall.

The diagnostic imaging technique of choice is computed tomography with intravenous contrast (CT angiography of the aorta). In this imaging test, a penetrating aortic ulcer appears as a focal outpouching of the aortic lumen. The contrast medium enters this lesion and gives the appearance of a crater-shaped protrusion of the lumen into the vascular wall. When this crater increases in size on consecutive imaging, then there is a clear indication that the lesion is unstable, with a risk of dissection or rupture of the aorta, and requires invasive treatment. Treatment is most often endovascular with the placement of an endovascular stent-graft.

Detail from a CT aortic angiography. The descending thoracic aorta (1) is atherosclerotic and aneurysmal with the presence of a penetrating ulcer (2) and intramural hematoma. (3. thoracic vertebral body)

The symptoms (pain) of a penetrating aortic ulcer are similar to those of aortic dissection, except that the penetrating ulcer usually does not cause aortic valve insufficiency or occlusion of arterial branches of the aorta. In some cases, an asymptomatic penetrating ulcer of the aorta may be found as an incidental finding on imaging performed for another indication. A penetrating aortic ulcer may develop complications such as intramural hematoma of the aorta, aortic dissection, pseudoaneurysm, or rupture of the aortic wall. Patients with penetrating ulcers have a higher risk of aortic rupture compared to patients with aortic dissection.

Regarding treatment, the same principles mentioned above also apply for an aortic intramural hematoma. That is, in type A penetrating ulcer, as a rule, surgical treatment is required, whereas for type B, medical treatment with clinical and imaging follow-up. In type B lesions with a complicated course (with signs of threatened rupture of the aorta) invasive treatment is performed (endovascular treatment with the placement of a stent-graft), whereas surgical treatment is performed when this is not technically possible.

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