3. Aneurysms & Dissection

Question 1

Definition of aneurysm

Answer 1

Localized abnormal dilation of a blood vessel or heart.

• True aneurysms involve an intact attenuated vessel/heart wall & may take on saccular (focal outward bulge) or fusiform (circumferential dilation) shapes.
• False aneurysms form in the case of a defect in the vessel wall leading to an extravascular hematoma bound by extravascular connective tissue which communicates with the intravascular space.

Question 2

Causes of aneurysms

Answer 2

1. Hypertension (mainly thoracic aortic aneurysms)
2. Atherosclerosis (mainly abdominal aortic aneurysms)
3. Tertiary syphilis
4. Polyarteritis nodosa
5. Trauma
6. Congenital defects (berry aneurysm)
7. Infections (mycotic aneurysms)
   - Embolization of a septic emboli (typically from infective endocarditis)
   - Extension of adjacent suppurative processes
   - Circulating organisms directly infecting arterial wall
   (e. g. bacteraemia from Salmonella gastroenteritis)

Question 3

Pathogenesis of aneurysms

Answer 3

1. Collagen degradation by local inflammation
   - Increased MMP, decreased TIMP
   - Occurs in atherosclerosis & vasculitis
2. Ischemia of media
   - Results in degenerative changes collectively called cystic medial degeneration (loss of smooth muscle cells & elastic fibres with increased production of amorphous ground substance)
   - Occurs in atherosclerosis (specifically inner medial ischemia due to thickening of intima which increases distances across which nutrients must diffuse to inner media) & hypertension (specifically outer medial ischemia due to narrowing of vasa vasorum)
3. Poor intrinsic quality of vascular wall connective tissue
   - Marfan Syndrome: fibrillin defect (a scaffolding protein), leading to aberrant TGF-beta activity with progressive weakening of elastic tissue
   - Loeys-Dietz Syndrome: TGF-beta receptor mutation
   which leads to abnormal elastin & collagen I & III
   - Ehlers-Danlos Syndrome: defective collagen III
   - Vitamin C deficiency

Question 4

Pathological effects & complications of aneurysms

Answer 4

1. Pressure on surrounding structures
   - [TAA] lungs, esophagus, recurrent laryngeal nerves, erode ribs & vertebrae
   - [AAA] ureter, erode vertebrae
2. Thromboembolism (due to disruption of laminar flow)
3. Occlusion of branch vessels
   - [TAA]: narrowing of coronary ostia
   - [AAA]: iliac, mesenteric, renal arteries
4. Rupture with hemorrhage
   - [TAA]: bleed into thoracic cavity
   - [AAA]: bleed into retroperitoneum or peritoneal
   cavity
   - [BA]: subarachnoid hemorrhage
5. Cardiac disease
   - [TAA]: dilation of aortic valve → aortic insufficiency

Question 5

Definition of dissection

Answer 5

Blood splaying apart laminar planes of the media to form a blood filled channel within the vessel wall, also known as the misnomer ‘Dissecting Aneurysm’

Question 6

Occurrence of aortic dissection

Answer 6

1. Hypertension (typically men aged 40-60)
2. Connective tissue abnormalities like Marfan Syndrome (younger patients)
3. Iatrogenic (catheterization, surgery)

Question 7

Classification of aortic dissection

Answer 7

1. Type A (more common & dangerous)
   - DeBakey I: ascending + descending aorta
   - DeBakey II: ascending aorta only
2. Type B
   - DeBakey III: occur after left subclavian artery root

Question 8

Pathogenesis of aortic dissection

Answer 8

1. Initiating event: intimal tear or rupture of vasa vasorum
2. Hemorrhage occurs in between middle & outer third of media
3. May dissect retrograde towards heart or distally
4. May rupture internally (through a second intimal tear,
   forming a double barreled aorta) or externally (bleeding into thorarcic/abdominal cavities or into pericardial sac)

Question 9

Pathological effects & consequences of dissection

Answer 9

1. Bleeding into pericardial (causing cardiac tamponade), pleural or peritoneal cavities
2. Aortic valve insufficiency (due to retrograde dissection)
3. Extension into aortic branches causing vascular
   obstruction & ischemic consequences (e.g. myocardial infarction with coronary artery occlusion)
4. Classic clinical symptoms: sudden onset of excruciating pain, usually beginning in anterior chest (may be confused with angina), radiating to the back between the scapulae, moves downwards as the dissection progresses