IMAGING OF AORTIC ANEURYSMAND AORTOARTERITIS

Aortic Aneurysms

• Aneurysm– A localized abnormal dilatation of an artery, vein,

or the heart.

• Aortic aneurysm– Thoracic– Abdominal– thoracoabdominal

Causes of aortic aneurysms

• Atherosclerosis(70-90%)• Traumatic ( 15-20%)• Congenital (2%)- aortic sinus, postcoarctation, ductus

diverticulum.• Syphilis• Mycotic • Cystic media necrosis( Marfan, Ehlers-Danlos

syndrome, annuloaortic ectasia)• Inflammation of media+adventitia-

– Takayasu arteritis, Giant cell arteritis, Rheumatic fever, Rheumatoid arthritis, Ankylosing spondylitis, Reiter syndrome etc.

CLASSIFICATION• TRUE VS FALSE

– True aneurysm- • all layers

– False aneurysm- • contained by

– adventitia or – perivascular connective tissue and organised hematoma.

• FUSIFORM VS SACCULAR– Fusiform aneurysm

• Circumferential involvement

– Saccular aneurysm• portion of a wall

Atherosclerotic aneurysm

• Cause - Atherosclerosis of the aorta• In elderly• Location

– Descending aorta distal to Left SCA.– Infrarenal aorta (a/w thoracic aneurysm in 29%)– Thoracoabdominal

• Fusiform- 80%• Saccular-20%

Mycotic aneurysm• Induced by bacteria invading arterial wall.• Predisposing factors

– IV drug abuse – Bacterial endocarditis (12%) – Immunocompromise (malignancy, steroids, chemo,

DM, etc.) – Infected prosthetic valves or sternal wires

• Organisms – S. aureus (53%) – Salmonella (33-50%) – Streptococcus – Mycobacterium ( contiguous spread from spine/lymph

node)• site Ascending aorta > visceral artery > intracranial artery >

upper/lower extremity artery.• Poor prognosis d/t quick expansion- rupture.• Imp to timely diagnosis bcz of poor prognosis.

Findings in mycotic aneurysm

1. Unusual location(noninfrarenal)2. Saccular aneurysm3. Rapid enlargement4. Irregular contour5. Lack of calcification6. Signs of infection

– Increase in periaortic fat– Perianeurysmal air– Perianeurysmal fluid collection with enhancing wall– Enlarged perianeursymal lymph nodes– Osteomyelitis of adjacent vertebra

Images obtained in a 73-year-old man with infected infrarenal aortic aneurysm associated with osteomyelitis and psoas muscle abscess. (a) Transverse contrast-enhanced CT scan shows an infrarenal aortic aneurysm (*) measuring 11 x 6 cm in

diameter associated with a left psoas muscle abscess (arrowhead) and vertebral body destruction (arrow). (b) Sagittal T1-weighted MR image shows abnormal signal intensity

(arrow) in the bone marrow of the vertebral body.

Abdominal aortic aneurysm

• Abdominal aortic aneurysms (AAAs) are segmental dilatations of the aortic wall that cause the vessel to be larger than 1.5 times its normal diameter or that cause the distal aorta to exceed 3 cm.

• These can continue to expand and rupture spontaneously, exsanguinate, and cause death.

• Prevalence: – Increases with age – Greater with atherosclerotic disease – Male predominance – Whites: Blacks = 3:1

Associated with: • visceral + renal artery aneurysm (2%) • isolated iliac + femoral artery aneurysm (16%)

– common iliac (89%), internal iliac (10%), external iliac (1%)

• stenosis / occlusion of celiac trunk / SMA (22%) • stenosis of renal artery (22-30%) • occlusion of inferior mesenteric artery (80%) • occlusion of lumbar arteries (78%)

• Clinical – asymptomatic (30%) – abdominal mass (26%) – abdominal pain (37%)

Anatomical classification• In relation to the renal arteries.

– Suprarenal– Juxtarenal (within 1.5 cm of renal artery origin)– Pararenal (involving one or both renal arteries)– Infrarenal

• ~90-95% of AAAs -infrarenal • Extension above renal arteries

– rare• Extension to common iliac arteries

– fairly common (66-70%).

Enlargement of AAA

• Over time, ~80% enlarge.• Most enlarge slowly.• Larger- faster.• smaller-slower• >=5cm 4-8mm/yr• 4-5cm 3-7mm/yr• <4cm 2-5mm/yr

Imaging modalities

• Plain x-ray: mural calcification (75-86%)

• US initial screening • If the aneurysm is approaching 5 cm or more

or if rapid enlargement is seen on serial US images

– CT and CTA/ MR and MRA– Angiography

Curvilinear calcification (arrowheads) is consistent with a significant size calcified abdominal aortic aneurysm.

The lateral view clearly shows calcification of both walls. Abdominal aortic aneurysm can be diagnosed with certainty- egg shell calcification.

USG

• >98% accuracy in size measurement• screening examination of choice as a result of

its relative availability, speed, low cost and no radiation.

• Problems with – obese pt, – distended bowel with gas, – proximal iliac arteries

US findings• Focal dilatation

beyond normal.• Any increase in the

size as the aorta travels distally is abnormal

• US findings of rupture– Partially encapsulated hematomas- a hypoechoic

or anechoic para-aortic space-occupying lesion.– Color Doppler-site of leak or extravasation,

CT-non-contrast

– perianeurysmal fibrosis (10%), may cause ureteral obstruction ( in inflammatory aneurysm)

– "crescent sign" = peripheral high-attenuating crescent in aneurysm wall (= acute intramural hematoma) = sign of impending rupture

CT-contrast-enhanced

• Accurately demonstrates dilation of the aorta• Extent of aneurysm• Degree of calcification, presence of mural thrombus, whole

aorta and iliac arteries • Major branch vessels proximally and distally-- helps in

determining the appropriate intervention (surgical or endovascular repair).

• Assessment of other abd organs possible. • CTA -multiplanar assessment of the aneurysm and associated

relevant vessels (visceral arteries, iliac and femoral arteries). • complications

CECT- Large thrombus.Angiogram underestimate the size of aneurysms in such case.

• Dilated abd aorta with mural calcification.

MRI• MRI and MRA good

alternatives in – impaired renal

function and – allergy to ICM

Angiography

• Often ordered for preoperative evaluation in patients with manifestations of atherosclerotic vascular disease such as renal artery stenosis or peripheral vascular disease.

• The role of angiography is in planning surgical or endovascular repair.

• Largely replaced by CTA or MRA if available.

Angio findings

• focally widened aortic lumen >3 cm • apparent normal size of lumen secondary to

mural thrombus (11%) • mural clot (80%) • slow antegrade flow of contrast medium• In rupture- not usually done in ruptured

aneurysm.

• Arteriogram -infrarenal abdominal aortic aneurysm.

• This arteriogram was obtained in preparation of an endovascular repair of the aneurysm

Lateral aortogram in a patient with severe mid back pain and lumbar spine images which demonstrated anterior erosion of the lower thoracic vertebral bodies. The

angiogram demonstrates that this has been caused by a pulsatile thoraco-abdominal aortic aneurysm.

Complications:

• Rupture (25%) • Peripheral embolization • Infection • Spontaneous occlusion of aorta

Rupture

• Sites• into retroperitoneum: commonly on left • into GI tract: massive GI hemorrhage • into IVC: rapid cardiac decompensation

High risk for rupture of AAA

• >5cm • Rapid growth ( >1cm per 6 months).• Mycotic aneurysm

Signs of AAA rupture

• Primary sign– Periaortic stranding– Retroperitoneal hematoma– Extravasation of IV contrast

• Secondary sign– High attenuating crescent sign– Focal discontinuity of intimal calcification– Tangential calcium sign– Draped aorta sign

High-attenuating crescent sign in a patient with subtle evidence of leak adjacent to the right psoas muscle (broad arrow).

Foccal discontinuity of intimal calcification

Tangential calcium sign:Intimal calcification pointsaway from the aneurysm andthere is retroperitoneal leakage.

LEFT: draped aorta sign.RIGHT: two weeks later there is a rupture

A positive aortic drape sign is considered to be present when the following features are seen: • area in which the posterior aortic wall is unidentifiable as a distinct line.• the posterior aorta follows the contour of the spine on one or both sides.

• Symptoms of rupture – sudden severe abdominal pain ± radiating into

back – faintness, syncope, hypotension

• Prognosis:64-94% die before reaching hospital

87-year-old man with known aneurysm and back pain. Enhanced CT image shows anterior aneurysm rupture (black arrow) with associated

retroperitoneal hemorrhage (white arrows).

False positive CT dx of aneurysm rupture

• Asymmetric aneurysm thrombus• Partial volume averaging of periaortic tissue at

the level of the aneurysm neck.• Perianeurysmal fibrosis( in NECT)• Unopacified 3rd and 4th portion of Duodenum.• Retroperitoneal lymphadenopathy.

Intervention

• Open surgery• Endovascular repair

Open surgery- indications(1) Any patient with a documented rupture or suspected

rupture; (2) a symptomatic or rapidly expanding aneurysm, regardless of

its size; (3) aneurysms larger than 5 cm in diameter; (4) complicated aneurysms with embolism, thrombosis, or

symptomatic occlusive disease. (5) atypical aneurysms (eg, dissecting, mycotic, saccular). These

guidelines must be weighed against the existing clinical risk factors in each patient

Pre-op assessment of AAA• We should assess :

– Maximum diameter of the aneurysm– Proximal and distal extent of aneurysm – Assessment of iliac and renal arteries– Perianeurysmal fibrosis– Congenital variations:

• Accessory renal arteries• Retroaortic course of left renal vein

• CT/CTA or MR/MRA is required for preop assessment.• USG is not enough because:

– Perianeurysmal soft tissue can not be assessed– Relation with renal arteries & congenital variations are difficult to

assess

Endovascular repair such as stent-graft placement

• evolving as an alternative to conventional, open surgical repair

• primary factors that determine suitability for endovascular repair are – diameter and length of the proximal neck of the

aneurysm- short and wide neck – poor fitting of stent.

– tortuosity of the aorta- poor fitting and – anatomy of the iliac arteries- long and large

common iliac artery poor anchorage.

• Endovascular devices rely on radial force to engage the more normal segments of the aorta and iliac arteries and to exclude blood flow from the aneurysmal sac.

THORACIC AORTIC ANEURYSM

• Aneurysmal dilatation of ascending, arch, or descending thoracic aorta.

• Aneurysm - localized or diffuse dilatation of more than 50% normal diameter of the aorta.

• Normal diameter– Aortic root 3.6 cm– AA 1 cm proximal to arch 3.5 cm– Prox des aorta 2.6 cm– Middle des aorta 2.5 cm– Distal des aorta 2.4 cm

Anatomical classicficationType Cause

1. Aneurysm of sinus of Valsalva

2. AA

3. AOA

4. DA

5. Aortic isthmus

1.Congenital, Syphilis

2. Atherosclerosis, Marfan syn, Ehlers-Danlos syn, syphilis, mycotic aneurysm

3. Atherosclerotic

4. Atherosclerotic

5. Post traumatic aneurysm

• Descending aorta aneurysms-m/c• Followed by ascending aorta aneurysms• Arch aneurysms occur less often.• Descending aortic thoracic aneurysms may

extend distally to involve the abdominal aorta and create a thoracoabdominal aortic aneurysm.

• Mean age 65 yrs• M:F 3:1• Clinical features

– Substernal/back/shoulder pain– SVC syndrome( venous compression)– Dysphagia(oesophageal compression)– Stridor, dyspnea( tracheobrncheal com)– Hoarseness( recurrent laryngeal nerve com)

Imaging of thoracic aneurysms:

• Main aim of imaging is to dx the aneurysm and find out the complication( dissection) as early as possible.

• Modalities: – CXR– CT/CTA– MR/MRA– Transesophageal echocardiogram (TEE)– Aortography

CXR

• Many readily visible on CXR.• Findings

– (1) widening of the mediastinal silhouette. – (2) enlargement of the aortic knob. – (3) displacement of the trachea from the midline.

Chest radiograph showing widening of the superior

mediastinum.

• TEE– excellent at detecting pericardial effusion and

aortic regurgitation, – 90% accuracy in imaging intimal membranes for

signs of aortic dissection– can be quickly performed at bedside under

sedation without radiation or the injection of contrast material.

• Disadv- poorly depicts aneurysms below the diaphragm and in the transverse aortic arch.

CT/CTA

• reliable test for diagnosing aneurysm and dissection, CTA gives anatomy.

• primary diagnostic test of choice in most institutions

• effective to define maximum diameter • To monitor diameter over time. • Findings:

– increase in aortic diameter:• A diameter >4 cm - aneurysm. • A diameter >6 cm- usually an indication for surgery

– outward displacement of calcium of the aortic wall.

Computed tomography image as maximum-intensity-projection showing calcification on the inner side of the aneurysm.

Ascending aortic aneurysm

MR/MRA

• Alternative of CT/CTA specially in pt with– impaired renal function and – allergy to ICM

• Velocity-encoded cine MRI – measurement of the differential flow velocity in

the true and false channels – to quantify the volume of concomitant aortic

regurgitation in patients with aortoannular abnormalities.

Aortography

• The criterion standard• But rarely used with the advent of TEE and CT• Still the preferred modality for

– preop evaluation of thoracic aortic aneurysms– for precise definition of the anatomy of the

aneurysm and great vessels.

Ascending aortogram showing ascending aortic aneurysm.

Aortic dissection

• Separation of the aortic intima with tear in it communicating with the true lumen.

• True lumen-inside the intima• False lumen-outside the intima • Most dissections arise either just distal to the

aortic valve or just distal to aortic isthmus

• Predisposing factors– Starts in fusiform aneurysms in 28 % cases– Hypertension (60-90%)– Marfan syn– Ehlers-Danlos syn– Trauma– Catheterisation – Aortitis ( not syphilis)

CLASSIFICATION SYSTEMS FOR AORTIC DISSECTION

Site of dissection Classification system

Crawford DeBakey Stanford

Both ascending and descending aorta

Proximal dissections

Type I Type A

Ascending aorta and arch only

Proximal dissections

Type II Type A

Descending aorta only (distal to left subclavian artery)

Distal dissections Type III IIIa—limited to thoracic aorta

IIIb—extends to abdominal aorta

Type B

Surgical intervention is required for type A dissection. In contrast, type B affectsonly the descending aorta and generally require only conservative medical treatment.

True versus false channel• False lumen:

– Anterior in the ascending aorta– larger caliber than true lumen– beak sign: acute angle with intimal flap at corner– intimal flap curved towards false lumen– thrombus is common– cobwebs due to medial strands– Slower flow in false channel on MR

• True lumen: – continues with the lumen of nondissected segment– Posterior and left lateral - descending aorta– smaller caliber– intimal calcification towards true lumen

61-year-old man with chest pain and acute type A aortic dissection. Axial enhanced CT scan of ascending aorta shows type A aortic dissection with

intimomedial tear (arrows) entering false lumen (F) from true lumen (T). DA = descending thoracic aorta, PA = pulmonary artery.

41-year-old man with acute aortic dissection. CT scan obtained at one-quarter distance along length of dissected portion of aorta shows descending aortic

dissection flap (arrows) that is curved toward false lumen (F). Beak sign (arrowheads) is present in false lumen. Note that false lumen area is larger than true lumen area

• Clinical features:– Sharp, tearing, intractable chest pain– Murmur or bruit of aortic regurgitation– Previously hypertensive, now possible shock– Asymmetric peripheral pulses– Pulmonary edema

Imaging Findings

• Chest X-ray: o Mediastinal wideningo Displacement of intimal calcificationso Apical pleural capo Left pleural effusiono Displacement of endotracheal tube or nasogastric

tube

• MRI– Intimal flap– Slow flow or clot in false lumen

• CT– Intimal flap– Displacement of intimal calcification– Differential contrast enhancement of true versus false

lumen • TEE

– Intimal flap

TEE view of the descending thoracic aorta in thehorizontal plane. An aortic dissection is manifested by the

presence of a true lumen (TL), a false lumen (FL), and afree-floating intimal flap (F). LA left atrium

Axial double-inversion-recovery MR images (TR/TE, 1875/18; inversion time, 150 msec) of 37-year-old man with Marfan syndrome. Image shows classic aortic

dissection with double-channel aorta. True lumen (straight arrow) is smaller than false lumen (curved arrow). High-velocity flow in true lumen causes signal void. Slower flow

with higher signal can be seen in false lumen.

Angiography– Intimal flap– Double lumen– Compression of true lumen by false channel– Increase in aortic wall thickness > 10 mm– Obstruction of branch vessels

AORTITIS

Causes of Aortitis• Takayasu arteritis• Rheumatic fever • Reiter’s syndrome • Syphilis

– Begins above sinotubular ridge

• Giant cell arteritis • Ankylosing spondylitis

– Crosses sinotubular ridge and dilates both root and ascending aorta

•Sinotubular Ridge-Jct of Sinuses of Valsalva and tubular aorta

Takayasu arteritis

• granulomatous vasculitis of unknown etiology

• commonly affects the thoracic and abdominal aorta

• causes intimal fibroproliferation of the aorta, great vessels, pulmonary arteries, and renal arteries

• results in segmental stenosis, occlusion, dilatation, and aneurysm formation in these vessels.

• Takayasu arteritis is the only form of aortitis that causes stenosis and occlusion of the aorta.

• Pathophysiology: – not fully elucidated to date. – begins as a nonspecific, cell-mediated

inflammatory process in the patient's first 2 decades of life and progresses to the formation of fibrotic stenoses of the aorta and its major branches.

Clinical Details: • 15-40 years• 8:1 females,• Early and late phases. • The early phase –

– inflammatory -prepulseless phase– Present with constitutional sign and symptoms with positive lab findings(Increased

ESR, positive C-reactive protein).– Radiological findings show only thickened vessel wall on CT and MR.– Angiography is usually negative.

• The late phase– occlusive -pulseless phase.– has thickening of media and adventitia. – Angiographic findings show smooth long segment stenosis and occlusions of the

proximal great vessels. • A 5- to 20-year interval bet two phases. • Presenting symptoms are Non-specific –

– fever, – arthralgias, and – weight loss.

Four types of late-phase Takayasu arteritis

• On the basis of the sites of involvement– Type I – aortic arch + brachiocephalic arteries.– Type II – thoracic aorta distal to arch, abdominal

aorta+ its major branches – Type III - Combination of type I and II – Type IV – any portion of the aorta with its

branches + pulmonary artery.

Preferred Examination

• Angiography - criterion-standard imaging • CTA and MRA :In the last 5 years, have

become equally valuable tools.

• Adv of CTA and MRA over conventional angio:– large fields of view, – noninvasive natures, – intravenously rather than intra-arterial contrast

material. – The increasing resolution of MDCT. – Particularly useful in pediatric groups who are

poor candidates for conventional angio.

• Adv of MRI over CT– Better soft-tissue contrast- valuable in

differentiating active versus quiescent forms of Takayasu disease.

– No use of ICM

Imaging Findings

• Angiography: The angiographic features occur late in the course of the disease and include– luminal irregularity– vessel stenosis, occlusion, dilatation, or aneurysms in the aorta

or its primary branches.– Neurofibromatosis of the abdominal aorta and some other

causes of mid aortic syndrome may produce an identical angiographic picture in children.

• CTA and MRA- thickened wall of aorta with crescents and indistinct outlines

• Associated aneurysms may be saccular or fusiform.• USG/Doppler study in accessible vessels. Shows wall

thickness and stenosis.

 Thoracic aortography in a young female with Takayasu aortoarteritis demonstrates concentric stenoses involving the left common carotid and left subclavian arteries (arrows).

 TA in a 22-year-old woman. Contrast-enhanced CT images at the level of the aortic arch (A) and at the level of the left pulmonary artery (B) demonstrate abnormal concentric wall thickening and periaortic inflammation of the aortic arch, ascending and descending aorta (arrows). (C) Sagittal reconstruction image demonstrates abnormal wall thickening of the aortic arch branches (arrowheads).

Coronal MRI of abdomen of 15-year-old girl with Takayasu arteritis. Note thickening and tortuosity of abdominal aorta proximal to kidneys.

Intervention

• Corticosteroid- acute phase• Bypass graft surgery is the procedure with the

best long-term patency rate • Percutaneous angioplasty:

– C/I in acute phase.– Best results with short-segment stenoses.

• Stent- reported in small numbers of cases. Most of the time not successful.

QUESTIONS

1. Causes of aortic aneurysm. 2. Classification of aortic aneurysm. 3. Finding in mycotic aneurysm. 4. Benefits of CT contrast in AAA. 5.Angiographic findings in AAA. 6.Signs of AAA rupture. 7. Indications of open surgery in AAA. 8. Classification systems for aortic dissection. 9. Difference between true and false lumen. 10. Imaging finding in aortic dissection. 11. Imaging finding in Takayasu arteritis.