An atheroma, plural atheromata, is a fatty, fibrous thickening in the wall of an artery that occurs as part of the process known as atherosclerosis, commonly referred to as hardening or narrowing of the arteries. Atheroma formation, or atherogenesis, is very widespread, affecting most people to some degree. The process begins in childhood and is found especially in populations eating a diet high in cholesterol. From middle age onwards, atherosclerosis frequently causes heart disease, strokes and circulation problems affecting the lower limbs, which can lead to gangrene in extreme cases.
Research is still going on to determine exactly how an atheroma is created, but the current theory is that the structures seem to arise at sites where there is injury to the artery wall. Certain points in the circulation, such as where branches occur, are subject to extra stress from blood flow and are more susceptible to damage, especially in people with high blood pressure. It is thought that substances from cigarette smoke, high levels of cholesterol in the blood, and possibly infection, could also cause injury to artery walls.
As well as causing damage, cholesterol can build up inside blood vessel walls, forming what are known as "fatty streaks," which may begin to appear in childhood. It is thought that the thickening often develops from the site of a fatty streak. Platelets, which are involved in blood clotting and blood vessel repair, move into the injured area and trigger the growth of muscle cells and a fibrous substance known as collagen, so that the atheroma becomes larger and more complex, forming what is called an atheromatous plaque. White blood cells, which have picked up cholesterol from the blood, move into the atheroma where they later die, causing a buildup of fat.
When the structure continues to grow, it makes an artery progressively narrower, with the result that the part of the body it supplies does not receive enough blood to function normally. If this happens in the heart, due to atheromatous plaques in the coronary circulation, it may cause a disease known as angina. Symptoms of angina typically include chest pain during exertion and breathlessness. The pain usually goes away with rest and can be treated with medication to relax the arteries, effectively widening them.
If the top of the structure breaks off to expose the interior, this can encourage a blood clot to form, and if this happens suddenly, the artery may block completely. When this takes place in the brain it can cause a stroke, while in the heart it may lead to a heart attack, both conditions requiring urgent treatment in the hospital. Lifestyle changes can help prevent atheromata, and giving up smoking, eating healthily and taking regular exercise have all been found to be effective.