Emboli arise from a variety of sources, including:
The heart from the left atrium in atrial fibrillation, the surface of an abnormal myocardium ( infarct, aneurysm, cardiomyopathy), bacterial or non-bacterial endocarditis, prosthetic or damaged valves (rheumatic fever, calcific aortic valve disease), malfunctioning valves (valve prolapse).
Cardiac neoplasm (atrial myxoma).
Paradoxical embolus in association with a congenital cardiac defect resulting in right to left shunt.
During cardiac surgery
Trauma causing fat emboli. This results in multiple petechial haemorrhages in the grey and white matter and can be demonstrated on frozen sections (Figure 19).
Foreign material such as cotton wool in drug abusers, therapeutic materials used in the treatment of vascular malformations
| Figure 19.|
Fat embolism. The section is a frozen section stained with oil-red O. There are early ischaemic changes in the adjacent white matter. This case followed trauma with fractured limb bones.
Gas - air (Figure 20) or nitrogen (decompression sickness).
| Figure 20.|
Air embolism. Note bubbles of air in veins on the surface of the brain.
The onset of embolic stroke is usually more rapid than thrombotic or haemorrhagic stroke.