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Aneurysms of blood vessels

By Dr. S.Homathy

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Aneurysm

• It is a localized dilatation of blood vessel or the heart due to a weakening of its wall.

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Classification

• Aneurysms may be classified by– type,– location,– the affected vessel. – Other factors may also influence the pathology and

diagnosis of aneurysms.

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True and false aneurysms• A true aneurysm– is one that involves all three layers of the wall of

an artery (intima, media and adventitia).

– True aneurysms include• atherosclerotic, • syphilitic,• and congenital aneurysms,• ventricular aneurysms that follow

transmural myocardial infarctions – aneurysms that involve all layers of the attenuated wall of the

heart are also considered true aneurysms

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• A false aneurysm or pseudo-aneurysm – does not primarily involve such distortion of the

vessel. – It is a collection of blood leaking completely out of

an artery or vein ( extravascular haematoma) – but confined next to the vessel by the surrounding

tissue. – It freely communicates with the intravascular

space (pulsating haematoma)– This blood-filled cavity will eventually either • thrombose (clot) enough to seal the leak • or rupture out of the tougher tissue enclosing it and

flow freely between layers of other tissues or into looser tissues.

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– Pseudoaneurysms can be caused by trauma that punctures the artery and

– are a known complication of percutaneous arterial procedures, such as• arteriography• arterial grafting, • or use of an artery for injection,

– such as by drug abusers unable to find a usable vein

– Ventricular aneurysm after MI that are contained by a pericardial adhesion

– Like true aneurysms, they may be felt as an abnormal pulsatile mass on palpation.

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Morphology

• Aneurysms are classified by their macroscopic shape and size and are described as either – saccular – fusiform.

• Saccular aneurysms are– spherical in shape and– involve only a portion of the vessel wall;– they vary in size from 5 to 20 cm (8 in) in diameter, and– are often filled, either partially or fully, by thrombus.

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• Fusiform ("spindle-shaped") aneurysms are– Involve diffuse, circumferential dilation of a long vascular

segment– variable in both their diameter and length;– their diameters can extend up to 20 cm (8 in). – They often involve

• large portions of the ascending and transverse aortic arch, the abdominal aorta, or

• less frequently the iliac arteries.

– The shape of an aneurysm is not pathognomonic for a specific disease

– Can involve• extensive portion of the aortic arch• Abdominal aorta• iliacs

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Location

• Cerebral aneurysms, also known as intracranial or brain aneurysms, – occur most commonly in the anterior cerebral

artery, which is part of the circle of Willis. – The next most common sites of cerebral aneurysm

occurrence are in the internal carotid artery

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• Many non-intracranial aneurysms arise – distal to the origin of the renal arteries at the

infrarenal abdominal aorta, • a condition some have postulated to be related

to atherosclerosis.

– However, increasing evidence suggests abdominal aortic aneurysms are a wholly separate pathology.• Trauma• Congenital defects• Infections (mycotic aneurysm)- syphilis• vasculitis

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• The thoracic aorta can also be involved.– One common form of thoracic aortic aneurysm

involves widening of the proximal aorta and the aortic root, which leads to aortic insufficiency.

• Aneurysms can also occur in the legs, particularly in the deep vessels (e.g., the popliteal vessels in the knee).

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Arterial and venous

• Arterial aneurysms are much more common, • but venous aneurysms do happen – example, the popliteal venous aneurysm

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Abdominal Aortic Aneurysms (AAA)

Definition• Diameter of the aorta 1.5 times

greater than normal.

• Most are infrarenal, and a significant number extend down into one or both iliac arteries

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Pathogenesis

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Primary Risk Factors

• Men over 60–Men are four times more likely to develop AAAs, but 20%

do occur in women.

• Smokers–Current smokers are seven times more likely to develop

AAA than non-smokers.–Former smokers are three times more likely.

• Family History–20% of AAA patients have a relative with the condition

Gene

Marfan,

Ehlers-Danlos syndrome

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Secondary risk factors

• Obesity • High blood pressure • High cholesterol • Atherosclerosis• Cardiovascular disease

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• Important causes of aortic aneurysm1. AS

• Intima infiltrated by atherosclerosis and thinned media.• Possible intraluminal thrombus and adventitia infiltrated by

inflammatory cells

2. Cystic medial degeneration of the arterial media

• Other causes include– Trauma– Congenital defects– Infections– Syphilis– vasculitis

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• Infection of the major artery weaken its wall–Mycotic aneurysm

• Can originate – From embolizationof a septic thrombus ( IE)– Extension of an adjacent suppurative process – Circulating organisms directly infecting the arterial

wall.

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Morphology

• Usually(about 90%) positioned below the renal artery and above the bifurcation of the aorta.

• AAA saccular or fusiform– As large as 15cm in dm and as long as 25 cm

• Aneurysm and nearby aorta often contain atheromatous ulcers covered by granular mural thrombi.– Prime site for atheroemboli that lodge in the vessels

of the kidneys or lower extremities

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• A thrombus frequently fills the part of the distal segment.

Two variant of AAA• Inflammatory AAA consist of dense periaortic

fibrosis containing an abundant lymphoplasmacytic inflammatory reaction– With many MP and often giant cells

• Mycotic AAAs– Atheromatous lesions become infected by circulating

organism in the wall– Destroy the media – rapid dilation and rupture

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Clinical features• Rupture into the peritoneal cavity- fatal

haemorrhage• Obstruction of a branch vessel – down stream

tissue ischaemic injury– Iliac- leg– Renal –kidney– Mesenteric- GIT– Vertibral branches- spinal cord

• Embolism from atheroma or thrombi• Impingment on an adjacent structure• Abdominal mass

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• Risk of rupture directly related to the size of the aneurysm

• If find any aneurysms refer to follow up• >5cm diameter –increased chance of rupture• <5cm –decreased chance of rupture

• Symptomatic aneurysms of any size = Emergency!!– Operative mortality of unruptured aneurysm is 5%– Operative mortality of ruptured aneurysm is >50%

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Syphilitic aneurysm

• Occurs in 3rd stage syphilis– Obliterative endarteritis

• Involvement of vasa vasorum of the aorta– Results in ischaemic medial injury– Leading to aneurysmal dilation of the aorta and

aortic annulus- eventually valvular insufficiency

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Morphology

• Home work

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Aortic Dissection (Dissecting haematoma)

• It is a catastrophic illness characterized by dissection of blood between and along the laminar planes of the media–With the formation of a blood- filled channel

within the aortic wall• that often ruptures outwards, causing massive

haemorrhage / cardiac tamponade

• May or may not associated with marked dilatation of the aorta

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Aortic Dissection– Prominent cause of sudden death– Violation of intima that allows blood to enter

media and dissect b/w intimal and adventitial layers

– Common site is ascending aorta at ligamentum arteriosum

• Unusual in the presence of substantial AS, syphilis ( medial scarring obstruct the advancement of dissection)

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Common presenting groups

• Occurs mainly in 2 groups of patients1. Men 40-60 years of age with antecedent HT

( 90% of cases)

2. Usually younger• Systemic or localized abnormality of connective

tissue that affect the aorta.• Eg: Marfan syndrome

3. Iatrogenic- complication of arterial cannulation

4. Congenital heart disease

5. Pregnancy

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Pathogenesis • HT is the major risk factor for aortic dissection–Medial hypertrophy of the vasa vasoum– Pressure related mechanical injury and / or

ischaemic injury

• Other rare causes include– Inherited or acquired CT disorders causing

abnormalvascular ECM• Marfan syndrome ( elongated axial bones, lens

subluxation, cardiovascular manifestations)• Vit C deficiency• Copper metabolic defects

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• Once the tear has occurred, blood flow under systemic pressure dissects through the media

• Fostering progression of the medial haematoma

• In some cases, disruption of the vaso vasorum can give rise to an intramural haematoma without an intimal tear

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Clinical Features

• The risk and nature of serious complications depend strongly on the level of the aorta affected

• Most serious complications with the involvment of aorta from the aortic valve to the arch

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– >85% abrupt, severe pain in chest or b/w scapula– 50% ripping or tearing– Pain in anterior chest –ascending aorta (70%)– Back pain (less common) –descending aorta (63%)– If dissection into carotid classic neurological

symptoms– 40% with neurologic sequelae (ex. paraplegia)– Nausea, vomiting, diaphoresis–Most have sense of impending doom

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Classification

Stanford Classification• Type A ( proximal and dangerous) -involves – Ascending aorta only or – ascending aorta, arch & descending aorta

• Type B –involves descending aorta

DeBakey Classification– Type I –ascending only– Type II –ascending, arch & descending aorta– Type III –descending only

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• Most common cause of death is rupture of the dissection outwards into the body cavity

• Retrograde dissection into the aortic root causes disruption of the aortic valvular apparatus– Cardiac tamponade– Aortic insufficiency–MI– Transverse myelitis (compression of spinal artery)– Critical vascular obstruction( extension of the

dissection into the great arteries)

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• The right carotid artery is compressed by blood dissecting upward from a tear with aortic dissection.

• Blood may also dissect to coronary arteries.• Thus patients with aortic dissection may have symptoms of

– severe chest pain (for distal dissection) or– may present with findings that suggest a stroke (with carotid dissection)

or– myocardial ischemia (with coronary dissection).

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• An aortic dissection may lead to hemopericardium when blood dissects through the media proximally.

• Such a massive amount of hemorrhage can lead to cardiac tamponade

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Morphology

In spontaneous dissection

• Intimal tear marking the point of origin( found in the ascending aorta within 10cm of the aortic valve)

• The dissection can extend along the aorta proximally towards the heart and distally

• Haematoma spreads characteristically along the laminar planes of the aorta between the middle and the outer thirds

• It often ruptures out causing massive haemorrhage

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• There is a tear (arrow) located 7 cm above the aortic valve and proximal to the great vessels in this aorta with marked atherosclerosis.

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• Some times rupture into the lumen creating a second or distal intimal tear– New vascular channel within the media of the

aorta ( double – barreled aorta with false channel).

–With time false channel become endothelialized- chronic dissection.

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• This aorta has been opened longitudinally to reveal an area of fairly limited dissection that is organizing.

• The red-brown thrombus can be seen in on both sides of the section as it extends around the aorta.

• The intimal tear would have been at the left. • This creates a "double lumen" to the aorta.• This aorta shows severe atherosclerosis which, along with

cystic medial necrosis and hypertension, is a risk factor for dissection.

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• Microscopically, • the tear (arrow) in this aorta extends through the media,• but blood also dissects along the media (asterisk).

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• In most cases, no specific causual pathology can be identified in the aortic wall

• Most pre-existing histologically detectable lesion is cystic medial degeneration – will be seen in Marfans and HT

• Elastic tissue fragmentation• Separation of elastic and fibromuscular

elements of the tunica media by small cleft like or cystic spaces filled with amorphous extracellular materials• Inflammation is characteristically absent.

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