Intimal hyperplasia is an exaggerated type of healing that occurs in the lining of blood vessels. It is a problem because it causes thickening of the blood vessel lining, which can narrow the interior of the vessel and obstruct normal blood flow. Intimal hyperplasia typically occurs in association with some forms of blood vessel surgery, procedures where vessels are widened using balloons and techniques where tubes are inserted to hold vessels open. Sometimes a bypass graft, where a blood vessel from another place is used to reroute flow past a blockage, can be affected by hyperplasia. There is no truly effective treatment, and research is ongoing into a solution for this problem.
The changes seen in intimal hyperplasia take place in the innermost layer of the blood vessel lining, known as the tunica intima. Usually, the hyperplasia process is triggered by damage to the lining. This may be caused by a procedure such as endarterectomy, where the buildup that causes narrowed arteries is cleaned out. White blood cells, platelets and other substances move into the damaged area, and special substances are released which influence muscle cells in the blood vessel wall. The muscle cells grow into the tunica intima, forming a firm scar that thickens the lining and narrows the blood vessel.
Although intimal hyperplasia causes problems, it is really an extreme form of a normal process that happens inside blood vessels all the time. The development of intimal hyperplasia is a particular problem in the treatment of coronary artery disease, where balloons are inflated inside narrowed arteries to widen them, and tubes called stents are inserted to hold the widened arteries open. Both the balloon inflation procedure and the insertion of a stent have the potential to damage the arterial lining and trigger intimal hyperplasia. If hyperplasia occurs, it usually develops around three months to a year after the procedure has taken place.
Doctors try to prevent intimal hyperplasia by ensuring as much as possible that they do not damage blood vessel linings during balloon inflations or stent insertions. Specially coated stents have been produced to prevent hyperplasia from extending inside the stent opening, but thickening can still occur at each end of the tube. Various drugs have been developed, and more options continue to be researched, to inhibit the onset of intimal hyperplasia. Traditional blood-thinning medications have also been used to try and combat the problem.