Thoracic aortic aneurysm
Definition: segmental, full thickness, dilation of a blood vessel having at least a 50 percent increase in diameter compared with the expected normal diameter.
Normal thoracic aortic diameter varies:
Male•
Aortic sinuses: 3.63 to 3.91 cm•Ascending aorta: 2.86 cm •Mid-descending aorta: 2.39 to 2.98 cm•At diaphragm: 2.43 to 2.69 cm
Female•
Aortic sinuses: 3.5 to 3.72 cm•Ascending aorta: 2.86 cm •Mid-descending aorta: 2.45 to 2.64 cm•At diaphragm: 2.40 to 2.44 cm
Classification:
1/ Location
●Ascending aortic aneurysms arise anywhere from the aortic valve to the innominate artery (60 percent)
●Aortic arch aneurysms include any thoracic aneurysm that involves the brachiocephalic vessels (10 percent)
●Descending aortic aneurysms are those distal to the left subclavian artery (40 percent)
●Thoracoabdominal aneurysms (10 percent)
2/ Extent
Classification according to Crawford
Type I arises from above the sixth intercostal space, usually near the left subclavian artery, and extends to include the origins of the celiac axis and superior mesenteric arteries. Although the renal arteries can also be involved, the aneurysm does not extend into the infrarenal aortic segment.
●Type II aneurysm also arises above the sixth intercostal space, and may include the ascending aorta, but extends distal to include the infrarenal aortic segment, often to the level of the aortic bifurcation.
●Type III aneurysm arises in the distal half of the descending thoracic aorta, below the sixth intercostal space, and extends into the abdominal aorta.
●Type IV aneurysm generally involves the entire abdominal aorta from the level of the diaphragm to the aortic bifurcation.
●Type V aneurysm arises in the distal half of the descending thoracic aorta, below the sixth intercostal space, and extends into the abdominal aorta, but is limited to the visceral segment.
3/Morphology
a- Fusiform: uniform, symmetrical dilatation that involves the entire circumference of the aortic wall;
b- saccular: appears as an outpouching of only a portion of the aortic wall. Saccular aneurysms may be a manifestation of plaque hemorrhage and aortic ulceration, or aortic wall infection and appear to have an increased risk for rupture
CLINICAL PRESENTATION
Usually silent unless a complication occurs. Discovered incidentally
Risk factors:
●Risk factors for atherosclerosis (eg, smoking, hypertension, hypercholesterolemia)
●Known aneurysm in the thoracic aorta or at other sites (eg, abdominal aortic aneurysm)
●Prior aortic dissection
●High-risk conditions – Marfan syndrome, Loeys-Dietz syndrome, vascular Ehlers-Danlos syndrome, Turner syndrome, or other connective tissue disease. Patients with these conditions may have a known mutation in genes known to predispose to TAA (FBN1, TGFBR1, TGFBR2, ACTA2, and MYH11).
●Known aortic valve disease (eg, bicuspid aortic valve, aortic valve replacement, or aortic stenosis)
●Family history of aortic dissection or thoracic aortic aneurysm
●Cerebral aneurysm
Patients can present initially with symptoms related to rapid expansion, which increases the risk for rupture, or complications such as aortic dissection or rupture.
Aortic arch – Ascending aneurysms can present with heart failure due to aortic regurgitation from aortic sinus dilatation and annular distortion. In addition, compression of a coronary artery can result in myocardial ischemia or infarction.
Large aneurysms affecting the transverse and descending arch can cause dysphagia from esophageal compression, hoarseness from left recurrent laryngeal nerve or left vagus nerve compression, or hemidiaphragmatic paralysis from phrenic nerve compression.
Descending aorta – Compared with ascending aneurysms, descending aortic aneurysms are less likely to lead to symptoms until the aneurysm has become very large.
The most serious complication of thoracic aortic aneurysm is rupture, most often into the left chest or pericardium, presenting as severe chest pain and hypotension or shock
Laboratory studies —
blood count, electrolytes, blood urea nitrogen and creatinine, D-dimer, and markers of cardiac ischemia
evidence of disseminated intravascular coagulation (elevated D-dimer) can be related to a large thoracoabdominal aneurysm
Anemia may point toward acute blood loss.
A negative D-dimer can be used to rule out aortic dissection in patients who present with chest pain, but it does not exclude the presence of an aneurysm.
ECG findings —
Signs of myocardial hypertrophy due to longstanding hypertension or valvular disease are more common, although nonspecific.
PHYSICAL EXAMINATION —
Vital signs in symptomatic patients may be normal, demonstrate sinus tachycardia, or moderate to severe hypotension.
Fever associated with TAA may indicate an infected aneurysm.
In patients with ruptured TAA, femoral and pedal pulses may be diminished or absent depending upon the patient’s blood pressure, the presence of peripheral artery disease, or thromboembolism. If lower extremity pulses are not easily identified, a hand-held continuous wave Doppler can be used to locate them.
Physical characteristics of associated high-risk conditions include the following:
●Marfan syndrome – tall stature, scoliosis, pectus deformities, elongated fingers and toes, hyperflexibility, and ocular abnormalities (eg, dislocated lens).
Loeys-Dietz syndrome has a characteristic triad of craniosynostosis, bifid uvula and hypertelorism.
●Familial TAA is associated with livedo reticularis, and iris flocculi
IMAGING DIAGNOSIS —
Incidental TAA —
Chest radiography:
Widening of the mediastinal silhouette
●Enlargement of the aortic knob
●Displacement of the trachea from midline
●Other features include displaced aortic calcification, aortic kinking, and opacification of the aorticopulmonary window.
Imaging asymptomatic, high-risk patients —
Consensus guidelines recommend aortic imaging in certain patient groups at high risk for TAA [2]. Patients with genetic mutations known to predispose to aortic aneurysms or aortic dissection (TGFBR1, TGFBR2, FBN1, ACTA2, or MYH11) should undergo complete aortic imaging (thoracic and abdominal aorta) at the time of their medical diagnosis. Aortic imaging is also recommended for first-degree relatives of patients with familial thoracic aortic aneurysm and/or dissection to identify those with asymptomatic disease. If one or more first-degree relatives of a patient with known thoracic aortic aneurysm and/or dissection are found to have thoracic aortic dilatation, aneurysm, or dissection, then imaging of second-degree relatives is reasonable.
Imaging symptomatic patients —
We suggest imaging the entire aorta. Disease of the abdominal aorta can occur in up to 20 percent of cases [39,40]. The study should also be of sufficient detail to assess branch vessel involvement.
AA often is initially diagnosed on transthoracic echocardiography (TTE) with the long axis view showing the aortic sinuses and proximal ascending aorta. When transthoracic imaging demonstrates an enlarged aorta, further evaluation with computed tomography (CT) or magnetic resonance (MR) is recommended.
CT is used more often in acutely symptomatic patients due to availability, efficiency, and proximity to the emergency department. The lack of ionizing radiation makes MR a more useful tool for patients who require repeated thoracic aortic imaging, such as those with known TAA or syndromes known to predispose to TAA.
MEDICAL MANAGEMENT OF ASYMPTOMATIC ANEURYSMS —
In the asymptomatic patient, medical management includes:
●Aggressive blood pressure control, with beta blockers being part of the regimen in an attempt to slow aneurysm growth.
●Surveillance for the development of signs and symptoms that may be associated with the aneurysm through patient education.
●Serial imaging of the aneurysm to evaluate growth and structure. The preferred imaging technique is CT scanning or MR angiography (image 4A-B). Imaging should be repeated at six months after the initial study [1]. Further imaging can be performed at yearly intervals if there is no growth.
Beta blockers may be of particular benefit for reducing the rate of aortic dilatation, particularly in adults with Marfan syndrome.Beta-blockers are thought to act by decreasing left ventricular contractility (dp/dt) and shear stress.
THORACIC ANEURYSM REPAIR —
Indications —
●The presence of symptoms.
●An end-diastolic aortic diameter of 5 to 6 cm for an ascending aortic aneurysm and 6 to 7 cm for a descending aortic aneurysm; often ≥7 cm in high-risk patients [8,13].
For smaller patients, including many women, elective repair is performed for aneurysms greater than twice the size of the nonaneurysmal aorta (normal segment).
●Replacement before aortic size index (aortic diameter (cm) divided by body surface area (m2)) for the ascending of aorta is 2.75 cm/m2 [14].
●Accelerated growth rate (≥10 mm per year) in aneurysms less than 5 cm in diameter [15].
●Evidence of dissection
●An ascending thoracic aortic aneurysm >4.5 cm in diameter at the time of aortic valve surgery.
MORBIDITY AND MORTALITY —
The subsets of aortic arch and Crawford type II (proximal descending to infrarenal aorta) aneurysms have the highest morbidity and mortality rates.
Death, paraplegia, paraparesis, stroke, or acute renal failure requiring dialysis
