3. Aneurysms & Dissection Flashcards
1
Q
Definition of aneurysm
A
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.
2
Q
Causes of aneurysms
A
- Hypertension (mainly thoracic aortic aneurysms)
- Atherosclerosis (mainly abdominal aortic aneurysms)
- Tertiary syphilis
- Polyarteritis nodosa
- Trauma
- Congenital defects (berry aneurysm)
- 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)
3
Q
Pathogenesis of aneurysms
A
- Collagen degradation by local inflammation
- Increased MMP, decreased TIMP
- Occurs in atherosclerosis & vasculitis - 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) - 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
4
Q
Pathological effects & complications of aneurysms
A
- Pressure on surrounding structures
- [TAA] lungs, esophagus, recurrent laryngeal nerves, erode ribs & vertebrae
- [AAA] ureter, erode vertebrae - Thromboembolism (due to disruption of laminar flow)
- Occlusion of branch vessels
- [TAA]: narrowing of coronary ostia
- [AAA]: iliac, mesenteric, renal arteries - Rupture with hemorrhage
- [TAA]: bleed into thoracic cavity
- [AAA]: bleed into retroperitoneum or peritoneal
cavity
- [BA]: subarachnoid hemorrhage - Cardiac disease
- [TAA]: dilation of aortic valve → aortic insufficiency
5
Q
Definition of dissection
A
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’
6
Q
Occurrence of aortic dissection
A
- Hypertension (typically men aged 40-60)
- Connective tissue abnormalities like Marfan Syndrome (younger patients)
- Iatrogenic (catheterization, surgery)
7
Q
Classification of aortic dissection
A
- Type A (more common & dangerous)
- DeBakey I: ascending + descending aorta
- DeBakey II: ascending aorta only - Type B
- DeBakey III: occur after left subclavian artery root
8
Q
Pathogenesis of aortic dissection
A
- Initiating event: intimal tear or rupture of vasa vasorum
- Hemorrhage occurs in between middle & outer third of media
- May dissect retrograde towards heart or distally
- May rupture internally (through a second intimal tear,
forming a double barreled aorta) or externally (bleeding into thorarcic/abdominal cavities or into pericardial sac)
9
Q
Pathological effects & consequences of dissection
A
- Bleeding into pericardial (causing cardiac tamponade), pleural or peritoneal cavities
- Aortic valve insufficiency (due to retrograde dissection)
- Extension into aortic branches causing vascular
obstruction & ischemic consequences (e.g. myocardial infarction with coronary artery occlusion) - 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
