Imaging of the Aorta Part 2
Part 2 review of aortic imaging for radiology board exams. Download the free study guide on this episode by clicking here.
Show Notes/Study Guide:
If a tardus parvus waveform is seen in both carotid arteries on ultrasound, what is the classic site of stenosis?
Bilateral tardus parvus waveforms should make you consider stenosis of the ascending aorta, in addition to the possibility of bilateral carotid stenoses.
What is the approximate aortic aneurysm size when surgery may be considered?
A thoracic aortic aneurysm over 6 cm in diameter for all patients, and >5 cm for patients with Marfan’s syndrome or other similar connective tissue disorders may meet criteria for surgical intervention. An abdominal aortic aneurysm > 5 cm may meet criteria for surgical intervention.
What are key findings to help distinguish the true lumen and false lumen in the setting of aortic dissection?
The true lumen is classically smaller than the false lumen. The true lumen may have outer wall calcifications, if present. Enhancement is often more rapid and homogeneous in the true lumen, whereas the false lumen often enhances less robustly and in a more delayed fashion and is more likely to thrombose. The true lumen typically continues into the more distal normal thoracic and/or abdominal aorta whereas the false lumen often ends. In a Type A dissection, the false lumen classically surrounds the true lumen.
True or false? The true lumen typically is located about the right anterolateral aspect of the ascending aorta and left posterolateral aspect of the descending aorta.
False. This describes the more common locations of the false lumen in the setting of aortic dissection.
True or false? The left renal artery more commonly arises from the false lumen.
True. If an aortic dissection involves the abdominal aorta, the left renal artery more frequently will arise from the false lumen. The origins of the celiac trunk, superior mesenteric artery, and right renal artery more commonly arise from the true lumen.
What is the cobweb sign of aortic dissection?
The cobweb sign refers to small strand-like areas of low attenuation that are projections of the aortic media that can be seen within the false lumen.
What are potential causes of a false-positive appearance for aortic dissection?
False-positive appearance of aortic dissection (sometimes termed pseudodissection) can result from motion artifact form aortic pulsation, contrast mixing, intramural or mural hematoma formation, and/or a penetrating atherosclerotic ulcer, and MRI susceptibility artifact.
What imaging strategy on CT can reduce pulsation artifact at the aortic root to improve evaluation of aortic dissections that may involve the aortic root?
EKG-gated chest CT angiography. The EKG gating will help remove pulsation artifact which can make evaluation of aortic dissection involving the aortic root challenging.
When does aortic dissection go to immediate surgical repair?
Classically, Stanford Type A dissections, and complicated type B dissections, go on to urgent surgical repair. Complications of Type A dissection that are best avoided include coronary artery occlusion, hemopericardium with cardiac tamponade, right heart failure due to compression of pulmonary arteries, and potential pulmonary artery intramural hematoma formation. Otherwise, blood pressure and heart rate control is generally first line therapy, such as treatment with beta-blockers.
What are key causes of aortitis to remember for board exams?
Key causes of aortitis for board exams include Takayasu arteritis, Giant Cell arteritis, and Cogan syndrome.
A few key points to remember for each of these:
Takayasu arteritis: Vasculitis that can affect the aorta, classically in young Asian women. This is sometimes nicknamed “pulseless disease”. Look for circumferential thickening of the aortic wall with smooth tapering and narrowing of the aorta and major branch vessels which may progress to occlusion. Other complications can include aortic valve regurgitation or stenosis and involvement of the pulmonary arteries.
Giant Cell arteritis: More common in older patients such as those over 50 years of age and is less likely to involve the aorta. Risk of vision loss for which early steroid treatment is often indicated.
Cogan syndrome: Classic pediatric vasculitis with characteristic eye and ear symptoms like optic neuritis, uveitis, possible aortitis.
Additionally, don’t forget other rheumatologic disorders as well as infectious causes of aortitis that can include syphilis, tuberculosis, and Salmonella pyogenic aortitis. Infectious aortitis can lead to mycotic aortic aneurysm formation.
What are classic clinical findings of abdominal aortic aneurysm rupture?
Abdominal aortic aneurysm rupture has a classic clinical triad of pain, hypotension, and a pulsatile abdominal mass, all of which is the result of hemorrhage into the retroperitoneum. If the rupture seals, this may become a somewhat chronic condition that may go undetected for weeks or months. On CT, look for retroperitoneal blood products adjacent to the aneurysm that may extend into the psoas musculature and perirenal spaces. Acute rupture may show extravasation. A high-attenuation crescent sign within an aneurysmal mural thrombus may also be evident.
What imaging findings are predictive of impending abdominal aortic aneurysm rupture?
Imaging findings that may portend pending abdominal aortic aneurysm rupture include size > 7 cm in diameter, serial size increase over 1 cm per year, aortic wall calcification discontinuity, a high-attenuation crescent sign, and reduced size over time of any intraluminal thrombus.
What are key imaging findings of the aorta in Marfan’s syndrome?
Aortic root dilatation is common as is mitral valve regurgitation from a degenerated mitral valve. Note a higher risk of aortic aneurysm and aortic dissection with Marfan’s syndrome, which is of particular concern with aortic root diameter over 5.5 cm and/or dilatation of the sinotubular junction. Other aortic pathologies can include aortic coarctation. Look for nearby pulmonary artery dilatation as well as pectus deformity.
What other inherited disorders increase risk of aortic aneurysm formation?
Beyond Marfan syndrome, remember Ehlers-Danlos syndrome, Loeys-Dietz syndrome, Noonan syndrome, autosomal dominant polycystic kidney disease, and osteogenesis imperfecta.
What is the leading risk factor for development of thoracic aortic aneurysm?
Elevated blood pressure is the leading risk factor for development of a thoracic aortic aneurysm.
Bicuspid aortic valves are associated with what type of thoracic aortic pathology?
Bicuspid aortic valves have a classic association with aortic coarctation, seen in about 70% of cases. Ascending aortic dilatation is also commonly seen. Remember the classic association of bicuspid aortic valves with Turner syndrome.
What are chest radiograph findings suggestive of aortic coarctation?
First, the “figure 3 sign” in which the aortic arch proximal to the coarctation is dilated, the left subclavian artery is dilated, and the distal aorta is dilated, with a narrowing noted at the coarctation site. Also look for inferior rib notching in long-standing cases of aortic coarctation, classically of the 4th through 8th ribs. If bilateral rib notching is seen, this means the coarctation is distal to the origin of each subclavian artery. Note that the 1st and 2nd ribs do not become notched as the 1st and 2nd intercostal arteries arise from the costocervical trunk and do not directly communicate with the thoracic aorta.