IMAGING OF AORTIC

PATHOLOGIES

Dr. Pankaj Kaira

JR-I Radiodiagnosis

SRMSIMS,Bareilly

Normal Anatomy of Thoracic and

Abdominal Aorta

The ascending aorta extends from the aortic valve to the origin of the innominate artery,withits 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 spindle

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.

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

The imaging options available for assessment of the

thoracic aorta include plain radiography, transthoracicechocardiography (TTE), transoesophagealechocardiography (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.

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 aneurysmalascending 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.

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 periadventitialtissues. It is saccular in shape.

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).

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.

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.

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).

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.

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.

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.

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).

MDCT

Widely available postprocessing techniques

include multiplanar reformation (MPR),

maximum intensity projection (MIP), curved

planar reformation, and 3D volume rendering

of the volumetric data.

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.

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

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

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 Marfansyndrome, connective tissue disorders, bicuspid aortic valve, Turner syndrome, aortic coarctation, aortic aneurysm, aortitis, pregnancy, and cocaine abuse.

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 subclavianartery). It requires surgical intervention.

Type B(25%) - do not involve the ascending aorta

(commencing distal to the left subclavianartery). Requires only conservative management.

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).

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.

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.

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).

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.

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).

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.

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.

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

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

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.

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).

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 ..

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.

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.

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.

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.

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.

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.

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.

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.

Thickened aortic cusps and pericardial effusionor

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.

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.

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 ligamentumarteriosum), 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”.

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.

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

hematoma in this patient.

THANK YOU