Thrombosis: formation of blood clots
When there is a high level of fat in the blood, excess lipids will adhere to the surface of the arterial wall, accumulate and eventually result in arteriosclerosis (hardening of the arteries). As the blood cannot run through these narrowed arteries smoothly, the heart will need to exert a higher pressure to push blood through, causing a rise in blood pressure.
Thrombosis at the brain is called Cerebrovascular Thrombosis.
Another possible cause of arteriosclerosis is the aggregation of platelets. When injuries occur in the blood vessels, platelets gather at the site of injury and begin the repair process. The walls of the blood vessels then become thicker and narrower, thus blood flow become slower, causing high blood pressure.