Atheroma, thrombosis, embolism and infarction Flashcards
What is an atheroma?
Fibro-fatty plaques
(porridge-like tumour)
Refers to plaques found particularly in elastic and medium-to-large muscular arteries
What is atherosclerosis?
Porridge-like hardness
The consequence of atheroma
What is arteriosclerosis?
Hardening of the arteries
Atheroma is one cause
Other causes include age-related sclerosis an calcification
Risk factors of atheroma
Age Male sex Genetics Hyperlipidaemia Hypertension Smoking Diabetes mellitus
Describe the pathogenesis of atheroma
Chronic endothelial injury/dysfunction
Accumulation of intimal lipid and foamy macrophages
Smooth muscle proliferation
Fibrosis forming a fibro-lipid plaque
Plaque injury- thrombosis and haemorrhage
What is the difference between a complicated and uncomplicated plaque?
Uncomplicated= thin fibrous cap Complicated= superimposed thrombi due to ulceration of thin cap= haemorrhage
Where do atheroma’s occur?
Elastic and medium-to-large muscular arteries
- Abdominal aorta
- Coronary arteries
- Popliteal arteries
- Descending thoracic aorta
- Internal carotid arteries
- Vessels of the circle of Willis (base of the brain)
What are the complications of atheroma?
Calcification Ulceration Plaque rupture Haemorrhage Thrombosis Aneurysmal dilation
What do the complications of atheroma lead to?
Vessel obstruction and downstream ischaemia
External vessel rupture may also occur, particularly with abdominal aortic aneurysms
What are the clinical implications of atheroma?
Cerebral infarction
Emboli in carotid arteries= TIA/ cerebral infarction
Myocardial infarction, cardiac failure
Aneurysm rupture causes sudden death
Peripheral vascular disease with intermittent claudication- thigh (impairment of walking)
Gangrene
What is a thrombus?
Solidification of blood constituents that forms within the vascular system during life
What is the difference between thrombus and blood clot?
Pathological process- denotes formation of thrombus within uninterrupted vascular system
Solidification of blood constituents outside the vascular system or after death is termed blood clot or haematoma (particularly if formed within tissues)
What are the risk factors for thrombosis?
Endothelial injury
Abnormal blood flow
Hypercoagulability
(Virchow’s Triad)
Describe endothelial injury
Ulcerated atheromatous plaques (aorta, carotid arteries, iliac and femoral arteries, coronary arteries)
Left ventricular endocardium after myocardial infarction
Abnormal cardiac valves (rheumatic fever, infective endocarditis, prosthetic valves)
Describe abnormal blood flow
Disrupts laminar flow
Prevents dilution of clotting factors
Retards the inflow of inhibitors of clotting factors
Promotes endothelial cell activation
What is turbulence?
Contributes to the development of arterial and cardiac thrombi
What is stasis?
Important in the formation of venous thrombi
Describe hypercoagulability
Alteration of the blood coagulation mechanism (particularly platelets and the clotting cascade) that in some way predisposes to thrombosis
May be a genetic predisposition (protein S/C deficiency)
May be acquired (after surgical procedures)
What are the types of thrombi?
Mural
Arterial
Venous
Describe a mural thrombi
Applied to one wall of the underlying structure
Occur in the capacious cavities of the cardiac chambers and the aorta
Describe arterial thrombi
Usually occlusive
May be mural
Frequent in coronary, carotid, cerebral and femoral arteries
Describe venous thrombosis
Also termed phlebothrombosis (not to be confused with thrombophlebitis)
Occurs typically in pelvic and leg veins in association with stasis
Describe the morphology of thrombi
Histological appearance typically shows alternating pale (band of fibrin and platelets) and dark (red band of red blood cells) ‘lines of Zahn’
What direct complications occur due to thrombosis in artery or vein?
Occlusion
Embolism- arterial= distal, venous= proximal
Arterial occlusion
What is arterial occlusion?
loss of pulses distal to thrombosis, area becomes cold, pale, painful, eventually tissue dies and gangrene results
What are the types of venous thrombosis?
Superficial (saphenous system)
Deep
Symptoms of superficial venous thrombosis
Congestion Swelling Pain Tenderness Rarely embolise
Symptoms of deep venous thrombosis
Foot and ankle oedema
May be asymptomatic and recognised only when they have embolised (to the lung)
What are the outcomes of venous thrombosis?
Resolution
Embolization to the lungs
Organised and incorporated into wall
Organised and recanalized
What is an embolus?
Detached intravascular solid, liquid or gaseous mass that is carried by the blood to a site distant from its point of origin
99% all emboli arise from thrombi (thromboembolism)
Implied unless otherwise qualified
What are the less common. rare forma of emboli fragments?
Bone or bone marrow Atheromatous debris Droplets of fat Tumour cells Foreign bodies (such as bullets) Bubbles of air or nitrogen
What are the types of embolism?
Pulmonary Systemic Amniotic fluid Air Fat
Describe pulmonary embolism
Embolism to pulmonary arteries
Occlusion of large or medium-sized pulmonary artery is embolic in origin until proved otherwise
Most arise in thrombi within the large deep veins of the lower leg
The next most common origin is pelvic veins, in association with pelvic masses
What is a ‘saddle’ pulmonary embolism?
Large emboli may impact in the main pulmonary artery or lodge at the bifurcation as a saddle embolus
Associated with collapse and sudden death- circulatory obstruction
What happens to smaller pulmonary emboli?
Travel out into the more periphery pulmonary arteries
If of intermediate size- cause pulmonary infarction (especially with cardiac failure)
If very small and recurrent- pulmonary hypertension
What is a paradoxical embolism?
In the presence of an interatrial or interventricular defect, they may gain access to the systemic circulation
Describe a pulmonary infarction
Typically haemorrhagic
The base of the infract faces the pleural surface
Patients present with haemoptysis- coughing up blood and/or pleuritic chest pain (pain on inspiration)
What is systemic embolism?
Emboli that travel through the systemic arterial circulation
80-85% arise through thrombi within the heart
What are the less common sources of thrombi developing from in systemic embolism?
Ulcerated atherosclerotic plaques
Aortic aneurysms
Infective endocarditis
Artificial heart valves and aortic grafts
What are the major sites for systemic emboli to lodge at?
Lower extremities (commonest)
Brain
Viscera (mesenteric, renal, splenic arteries)
Upper limbs (much less common)
What is an infarct?
Area of ischaemic necrosis caused by occlusion of arterial supply or venous drainage in a particular tissue
What is necrosis?
Refers to spectrum of morphological changes that follow cell death in living tissue largely resulting from the progressive action of enzymes on the lethally injured cells
Causes of infarction
Thrombosis/ thromboembolism Vasospasm Expansion of atheroma Compression of a vessel Twisting of the vessels through torsion Traumatic rupture
What are the factors that influence the development of an infarct?
- Nature of the vascular supply (single= spleen, dual= lung, small bowel)
- Rate of development of occlusion (rapid more likely to cause infarction)
- Vulnerability of affect tissue to hypoxia (more metabolically active tissues more vulnerable= heart)
- Oxygen content of blood (hypoxia increases risk)
What are the types of infarct?
- Red (haemorrhagic)= venous occlusion (torsion)/ loose tissues/ tissues with a dual circulation (lung)
- White (anaemic)= arterial occlusions/ solid organs (heart/ spleen)
- Septic (infected infarcts)
Describe a haemorrhagic infarct
Ovarian infarct
Venous occlusion as a result of torsion
Dark blue and haemorrhagic
Describe the types of anaemic infracts
- Splenic= wedge-shaped, white
- Renal infarct= wedge-shaped, white, rim of hyperaemia (an excess of blood in the vessels supplying an organ)
Describe the histopathology of infarction
- Ischaemic coagulative necrosis (mins-days)= CNS
- Inflammatory response (hrs- 7 days)
- Reparative response (1-2 wees)
- Scarring (2 weeks- 2 months)
