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IMAGING OF AORTIC PATHOLOGIES Dr. Pankaj Kaira JR-I Radiodiagnosis SRMSIMS,Bareilly
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Normal Anatomy of Thoracic and Abdominal Aorta The ascending aorta extends from the aortic valve to the origin of the innominate artery,with its proximal portion referred to as the “aortic root.” The aortic arch begins at the innominate artery and ends at the ligamentum arteriosum. Its most distal aspect, which is often slightly narrowed, is termed the “aortic isthmus.” The descending aorta begins at the ligamentum. Its proximal portion may appear slightly dilated and has been termed the “aortic
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Branches of Aorta The innominate artery is the first and typically the largest branch and is usually seen more caudally than the other branches on transverse CT images. It gives rise to the right subclavian and right common carotid arteries. The left common carotid artery arises next at a more cephalad level and has the smallest diameter of the three major arterial branches. The left subclavian artery is the third branch and arises from the posterior superior portion of the aortic arch.
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Abdominal Aorta The abdominal portion of the aorta extends from the diaphragm to the level of the fourth lumbar vertebra, where it bifurcates into the right and left common iliac arteries. The abdominal aorta gives rise to important single and paired branches. The single branches arise anteriorly and supply the anterior abdomen, whereas the paired branches arise laterally and supply the posterior abdomen. The single branches include The celiac trunk The superior mesenteric artery The inferior mesenteric artery The unpaired middle sacral artery arises from the posterior terminal portion of the abdominal aorta . The paired abdominal aorta branches are, from cephalad to caudad The inferior phrenic arteries, suprarenal and renal arteries, gonadal arteries, and several paired lumbar arteries
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The imaging options available for assessment of the thoracic aorta include plain radiography, transthoracic echocardiography (TTE), transoesophageal echocardiography (TOE), multidetector CT, MRI and invasive catheter angiography. The chest radiograph (CXR) can serve to raise suspicion of aortic disease by demonstrating an abnormal mediastinal contour in patients being investigated for other reasons. Computed tomography (CT) and magnetic resonance imaging (MRI) are the most commonly used imaging examinations to evaluate thoracic aortic diseases because of their high spatial and temporal resolutions, large fields of view, and multiplanar imaging reconstruction capabilities.
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Aortic Aneurysm An aneurysm is defined as a permanent dilatation of the aorta exceeding the normal measurements by more than 2 SDs at a given anatomic level. Most Common cause of Thoracic aneurysm – Atherosclerosis. Most Common cause of Ascending aortic aneurysm – Cystic median necrosis. It is most frequently caused by Marfan syndrome, but in one third of the cases it is idiopathic. In Marfan syndrome, the classic imaging features include a pear-shaped aneurysmal ascending aorta with smooth tapering to a normal aortic arch. Other causes of aortic aneurysm include aortic dissection, bicuspid aortic valve, coarctation, Ehlers-Danlos syndrome, Loeys-Dietz syndrome, syphilis and other infections, arteritis, or trauma. Less common causes include ankylosing spondylitis, rheumatoid arthritis, rheumatic fever, systemic lupus erythematosus, scleroderma, Behcet disease, psoriasis, ulcerative colitis, Reiter syndrome, and radiation therapy. The prevalence of thoracic aortic aneurysms increases with age, with an overall incidence approximating 450 per 100,000 and a 3:1 male predominance. In up to one third of cases, the abdominal aorta is also involved.
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Types of Thoracic aortic aneurysm : (a) True aneurysms - All three layers of the aortic wall (intima, media, and adventitia) are involved without disruption of any layers. It is fusiform in shape. (b) False aneurysms (also referred to as pseudoaneurysms), the intima is disrupted (and often, the media as well),and blood is contained by the adventitia and periadventitial tissues. It is saccular in shape.
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55-year-old asymptomatic woman with incidentally detected ascending aortic aneurysm. Contrast-enhanced CT image shows incidental ascending aorta aneurysm with widening of aorta to 5.5 cm (arrow).
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Pseudoaneurysm—coronal reconstructed CT image in a 53-year-old male following aortic surgery shows a pseudoaneurysm with narrow neck originating from the lateral aspect of the ascending aorta.
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70-year-old man with diffuse abdominal pain. Three-dimensional volume rendering of contrastenhanced CT scan shows fusiform aneurysm of distal abdominal aorta without extension into iliac arteries. Note narrowing of right common iliac artery (arrow). Atherosclerotic plaque is highlighted in blue and contrast- opacified lumen in pink.
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70-year-old woman with shortness of breath. Contrast-enhanced CT image shows large fusiform descending aortic aneurysm (AA) causing extrinsic compression of adjacent bronchi with luminal narrowing (arrows).
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Saccular aortic root aneurysm—(a) short axis reconstructed CT image showing a giant aneurysm of the aortic root, originating from the right sinus of Valsalva. (b) Coronal reconstructed CT image shows the saccular aneurysm with narrow neck originating from the right sinus of Valsalva.
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Abdominal aortic aneurysm The vast majority of abdominal aneurysms are caused by atherosclerosis. Dilatation of the abdominal aorta greater than 2 cm is considered abnormal, but a diameter of more than 3 cm is considered diagnostic of an abdominal aortic aneurysm. Abdominal aortic aneurysm most often involves the infrarenal segment of the aorta.
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Thoraco-abdominal aneurysm Crawford and DeNatale classification on the basis of anatomic location. Type I - involves the descending thoracic aorta below the origin of the left subclavian artery and the upper abdominal aorta. Type II - involves both the thoracic descending aorta and most of the abdominal aorta. Type III - is restricted to the lower portion of the thoracic aorta. Type IV - begins at the diaphragm and extends caudally.
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Imaging On both MDCT and MRI, the key features for imaging assessment of aneurysms are maximal aortic diameter; shape and extent; involvement of aortic branches; relationship to adjacent structures, such as the bronchi and esophagus; and presence of mural thrombus (especially if the patient presents with peripheral embolization symptoms).
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MDCT Widely available postprocessing techniques include multiplanar reformation (MPR), maximum intensity projection (MIP), curved planar reformation, and 3D volume rendering of the volumetric data.
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MRI MRI is a robust tool for evaluation of aortic aneurysms. Three-dimensional contrast-enhanced MR angiography (MRA) is highly accurate at depicting the location, extent, and precise diameter of an aneurysm and its relationship to the aortic branch vessels. MRI displays mural thrombus as intermediate signal material on standard spin-echo T1- weighted images, but it does not reliably detect calcifications in the aortic wall. With this technique, the patent lumen can be seen as a flow void.
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Complications: The most frequent complications of aortic aneurysm—mass effect, dissection, and rupture—are directly related to size. The mean rate of dilatation for thoracic aortic aneurysm is 0.12 cm per year. The risk of rupture increases with increasing aortic diameter, with a high risk of complications (rupture and dissection) at 6 cm for the ascending and 7 cm for the descending aorta. Diagnostic findings include active contrast extravasation or high-attenuation hemorrhagic collections in the pleura, pericardium, or mediastinum CT angiography is the investigation of choice. Another complication of abdominal aortic aneurysm is aortoduodenal fistula, which may be associated with recurrent and potentially catastrophic bleeding. CT can detect this condition by showing loss of the normal fat plane between the aorta and duodenum and the presence of air in the aorta
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69-year-old man with worsening abdominal pain. Contrast-enhanced CT image shows aortic aneurysm with active extravasation of contrast material within aneurysm (arrow). Left-sided hemothorax (asterisk) is secondary to rupture
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Aortic Dissection Aortic dissection is the most common acute aortic disorder, with an incidence up to 0.2–0.8%, and also carries the highest mortality rate. It is characterized by a tear in the tunica intima of the aorta, with resultant leak of blood into the tunica media and formation of a false lumen. It is usually the result of systemic hypertension. Other causes of aortic dissection include Marfan syndrome, connective tissue disorders, bicuspid aortic valve, Turner syndrome, aortic coarctation, aortic aneurysm, aortitis, pregnancy, and cocaine abuse.
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Classifications: Stanford Classification: It is the widely used classification as it guides the treatment. Type A(75%) - involves the ascending aorta (commencing proximal to the left subclavian artery). It requires surgical intervention. Type B(25%) - do not involve the ascending aorta (commencing distal to the left subclavian artery). Requires only conservative management.
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This 24-year-old man with Marfan’s syndrome presented with acute chest pain. He has a large ascending aortic aneurysm but the separate Type B dissection in the descending aorta was the cause of the acute presentation. The arrow demonstrates the acute angle between the intimal flap and the aorta wall, indicating that the false lumen is anterior. The superior vena cava is compressed by the ascending aortic aneurysm (arrowhead).
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Patients with acute aortic dissection usually present with one or a combination of the following symptoms: chest pain radiating to the back, syncope, and shortness of breath. Acute aortic dissection is defined as dissection detected within 2 weeks of the onset of symptoms, whereas chronic dissection is defined as older than 2 weeks.
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Imaging on MDCT Unenhanced CT : Medially displaced aortic calcifications or the intimal flap itself. Unenhanced images are also important for detecting intramural hematoma. Contrast enhanced CT : The key finding on contrast-enhanced images is an intimal flap separating two lumens. The convexity of the intimal flap is usually toward the false lumen that surrounds the true lumen. The false lumen usually has slower flow and a larger diameter and may contain thrombi. The true lumen maintains direct continuity with the undissected proximal normal aorta and is usually smaller than the false lumen.
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65-year-old man with abdominal pain. A, Unenhanced, low-dose CT image shows displaced intimal calcifications (arrow) in Stanford type B dissection. B, After contrast administration, intimal flap is seen separating true and false lumen (arrow).
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66-year-old woman with chest pain. A, Contrast-enhanced CT shows descending aortic dissection with small anterior true lumen and posterior false lumen. Arrow points to cobwebs in false lumen. Note is made of incidental spinal bone island. B, Sagittal reformation image confirms posteriorly located false lumen with cobwebs (arrow) and wellopacified anterior true lumen.
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75-year-old man with chest pain and hypotension. Intimal flap (black arrow) in Stanford type B dissection separates smaller anterior true lumen from posterior false lumen of descending aortic aneurysm complicated by rupture, seen as active extravasation of contrast material (white arrow).
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Usually, in type A aortic dissection, the false lumen is located along the right anterolateral wall of the ascending aorta and extends distally in a spiral fashion along the left posterolateral wall of the descending aorta. Slender linear areas of low attenuation may be observed in the false lumen and represent the residua of incompletely dissected media and are known as the cobweb sign, a specific finding for identifying the false lumen. MRI - An intimal flap remains the key finding, usually seen first on spin-echo black blood sequences. Additional findings include signal void in the true lumen and higher signal intensity indicative of turbulent flow in the false lumen.
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Intramural hematoma Intramural hematoma is defined as a bleeding of the vasa vasorum in the medial layer of the aorta, with no blood flow within the media . Systemic hypertension is the leading cause. Other causes – Aortic trauma, penetrating aortic ulcer.
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Intramural hematoma most frequently involves the ascending or proximal descending aorta—up to 70% of cases. Intramural hematoma is classified in the same way as aortic dissection: type A when the ascending aorta is involved and type B when involvement is limited to the descending aorta
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Imaging MDCT : A high-attenuation crescenteric thickening of the aortic wall that extends in a longitudinal, nonspiral fashion is the hallmark of this entity. In contrast to dissection, the aortic lumen is rarely compromised, and no intimal flap or enhancement of the aortic wall is seen after contrast administration. On contrast-enhanced CT, the hematoma shows no enhancement and maintains a constant circumferential relationship with the aortic wall
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MRI : May also provide a determination of the age of a hematoma based on the signal characteristics of different degradation products of hemoglobin. For example, T1- weighted spin-echo images show intermediate signal intensity caused by the presence of oxyhemoglobin in the acute stage and high signal intensity caused by the presence of methemoglobin in the subacute stage.
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50-year-old woman with acute chest pain. A, Unenhanced low-dose CT image shows relatively high- density intramural hematoma surrounding descending aorta (arrow). B, On contrast-enhanced CT image, intramural hematoma is visually less conspicuous (arrow).
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A 66-year-old male presented with acute chest pain. non-contrast-enhanced CT angiogram (a), which shows the hyperdense rim of an intramural haematoma (IMH) in the descending aorta (arrow). MRI was performed to determine if the ascending aorta was involved, which is confirmed (horizontal arrows) with ‘‘black blood’’ half-Fourier acquisition single-shot turbo spin echo (b) and balanced steady-state free precession images ..
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post-contrast study was performed, which shows a focal out-pouch of contrast into the atheroma in the distal arch typical of a penetrating atherosclerotic ulcer. A noncontrast-enhanced CT would have helped by showing the acute IMH as a hyperdense rim.
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Penetrating Atherosclerotic Ulcer These are defined as an atherosclerotic lesion that penetrates the elastic lamina, usually leading to a haematoma within the media, but also potentially to true dissection or rupture. Embolization of material from the ulcer to the distal arterial circulation is an additional recognized complication. Elderly hypertensive patients are most frequently affected, and the mid descending thoracic aorta is most commonly (90%) involved.
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Imaging MDCT: On unenhanced MDCT, penetrating aortic ulcer appears as an intramural hematoma. Contrast-enhanced MDCT, including axial and multiplanar reformations, is the technique of choice for diagnosis of penetrating aortic ulcer. Localized ulceration penetrating through the aortic intima into the aortic wall is the characteristic finding, usually in the mid to distal third of the descending aorta. Focal thickening or high attenuation of the adjacent aortic wall suggests associated intramural hematoma.
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Penetrating atherosclerotic ulcer—axial postcontrast CT scan in a 48-year-old male with acute chest pain shows contrast outpouching from the anterior aspect of descending thoracic aorta (arrow), consistent with a penetrating atherosclerotic ulcer.
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Rupture of Aorta Rupture of an aneurysm, dissection, or penetrating ulcer can be contained or can be free when it extends into the mediastinum, pericardium, pleura or extrapleural space, esophagus,or bronchus. Ruptured aneurysms are often diagnosed clinically, but if imaging is required, CT is the modality of choice. Contrast-enhanced CT shows active extravasation into the adjacent tissues. Impending rupture manifests on CT by the presence of a high attenuation “crescent” within mural thrombus of an aneurysm. Contained rupture is characterized lack of distinction between the posterior wall of the aorta and adjacent structures such as the vertebrae a result of contained rupture of the posterior aortic wall, a finding referred to as the “draped aorta” sign.
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Contained rupture—(a) noncontrast CT scan in a patient presenting with acute chest pain shows nonspecific soft tissue adjacent to descending thoracic aorta. (b) Contrast enhanced CT at the same level shows lack of distinction between the posterior wall of the aorta and the adjacent vertebral body, the “draped aorta” sign (curved arrow), which is indicative of a contained rupture.
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Aortitis Aortitis (vasculitis) is characterized by presence of leucocytes in the aorta wall, with reactive damage to mural structures. Takayasu arteritis and giant cell arteritis are the most common vasculitides to affect the aorta.
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Takayasu arteritis is an idiopathic arteritis that is more common in women, particularly Asians. It destroys the arterial media, resulting in aneurysms and rupture. It typically affects the aorta and its primary branches and can involve a focal region of the aorta or the entire vessel. Takayasu arteritis can be aneurysmal or occlusive. CT and MRI can show thickening of the vessel wall and mural contrast enhancement in early stages; stenoses, occlusion, and aneurysms characterize the later stages. MRI shows wall thickening and high signal intensity on T2-weighted STIR images due to edema in acute stages.
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T2-weighted triple inversion recovery black blood image in the same patient with Takayasu arteritis shows very high signal of the thickened aortic arch (arrows), which is consistent with edema, indicative of active arteritis.
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Giant cell (temporal) arteritis is a chronic vasculitis of large and medium size vessels that typically affects the temporal arteries and is associated with polymyalgia rheumatica. The large vessel type of giant cell arteritis affects the aorta and its branches, particularly the subclavian arteries.
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Coarctation of Aorta Aortic coarctation is the most common congenital defect, making up around 7% of all congenital heart lesions. It consists of a focal stenosis, commonly at the aortic isthmus (between the left subclavian artery and ligamentum arteriosum), but can occur in a more tubular fashion in the mid-aortic arch. Children and adults can present with angina pectoris and leg claudication. On clinical examination, diminished femoral pulses and differential blood pressure between upper and lower extremities may be noted X-ray shows classical signs of “Figure of 3” and “Inferior rib notching”.
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Traumatic Aortic injury Aortic injury is a serious sequela of blunt chest trauma. The most common site for aortic injury is in the ascending aorta. The most common location of injury in patients undergoing imaging is the arch at or near the level of ligamentum arteriosum. Direct CT findings of acute aortic injury include deformity of the aortic contour ,intimal flap, intraluminal debris, pseudoaneurysm, and intramural hematoma. CT is more sensitive than angiography in the detection of subtle aortic injuries.
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Acute traumatic aneurysm—postcontrast axial CT scan image in a 28-year-old male who was involved in a motor vehicle accident shows a small focal outpouching from the anterior aspect of the proximal descending thoracic aorta (curved arrow), which is indicative of aortic trauma. Note the absence of mediastinal
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