Infarction& embolism

Question 1

What is the difference between thrombosis & embolism?

Answer 1

• Thrombosis refers to the formation of blood clots ( blocking an artery/vein)
• Embolism refers to the transfer of abnormal material by the blood stream & its impaction in a vessel

Question 2

Define infarction

Answer 2

An infarct is an area of ischaemic necrosis within a tissue or organ, produced by occlusion of either its arterial supply or its venous drainage

Question 3

What is the common cause of infarcts?

Answer 3

Acute arterial occlusion

1. ) Thrombosis e.g coronary arteries —> myocardial infarct
2. ) Embolism e.g lung,kidney, spleen
3. ) Either thrombosis or embolism e,g brain (but also hypotension)

Question 4

Why is venous infarction less common?

Answer 4

-Most tissues have numerous venous anastomoses so arrest of blood due to venous obstruction is unusual

Question 5

When can venous infarction occur?

Answer 5

1. )Thrombosis of the mesenteric veins= intestinal infarction
2. ) Thrombosis in the superior sagittal (longitudinal) sinus= infarction in the brain
3. ) occurs in the testis/ovary following torsion

Question 6

Outline the two types of myocardial infarction

Answer 6

1. ) Transmural infarct (commonest): the ischaemic necrosis involves the full or nearly full thickness of the ventricular wall in the distribution of a single coronary artery
   - Usually associated with coronary atherosclerosis, plaque rupture& super-imposed thrombosis
2. ) Subendocardial infarct: constitutes an area of ischaemic necrosis limited to the inner one-third, or at most one-half, of the ventricular wall
   - There is diffuse stenosing coronary atherosclerosis and global reduction of coronary flow (e.g due to shock) but no plaque rupture and no thrombosis

Question 7

Outline the different types of infarction in terms of classification by colour and bacteria

Answer 7

• Infarcts are divided on their colour ( red or haemorrhagic vs white/pale/anaemic) and the presence ( septic infarcts) or absence( bland infarcts) of bacteria
• White infarcts occur:
  1. ) With arterial occlusion
  2. ) In solid tissues e.g heart, spleen, kidneys

Question 8

Explain the morphological complications that may arise following MI

Answer 8

1. ) CARDIAC RUPTURE: Due to the mechanical weakening that occurs in nephrotic & inflammed myocardium
   - Commonest at 4-7days post-infarct
   - Most commonly involves the ventricular free wall resulting in haemopericardium& cardiac tamponade
   - Rupture of interventricular setptum results in left-to-right shunt
   - Rupture of papillary muscle results in severe acute mitral incompetence
2. ) PERICARDITIS: usually develops about the 2nd/3rd day. It’s fibrinous or fibrinohaemorrhagic & is usually localised to the region overlying the necrotic area
3. )MURAL THROMBOSIS: the combo of a local myocardial abnormality in contractility( causing stasis) & endocardial damage ( causing a thrombogenic surface) leads to mural thrombosis& thromboembolism
4. )VENTRICULAR ANEURYSM: A late complication that most commonly results from a large anteroseptal, transmural infarct that heals into a large area of thin scar tissue that paradoxically bulges during systole

Question 9

Define embolism

Answer 9

The transfer of abnormal material by the blood stream and its impaction in a vessel
-The impacted material= the embolus

Question 10

List the different types of emboli

Answer 10

• Fragments of thrombus (commonest)
• Material from ulcerating atheromatous plaques (common in distal leg arteries)
• septic emboli
• fragment of tumour growing into a vein
• Fat globules
• Air emboli
• Parenchymal cells

Question 11

Outline DVT & PE

Answer 11

• PE= very common
• PE results from detachment of a thrombus in a systemic vein, usually in the deep venous plexus in the leg ( hence DVT)
• PE= commonest around the 10th post-operative day
• may cause sudden death
• Large thrombi may be detached as a group going to the right side of the heart. This causes sudden blockage of the pulmonary trunk or a major division. Death is either immediate or after a short period of respiratory distress
• Fatal emboli are usually derived from the femoral and iliac veins. Form a cylinder about 1cm diameter & up to 30cm long. At autopsy they are found coiled like a snake in pulmonary artery & right ventricle
• Less gross fragments impact in major or minor pulmonary arteries