small blood vessel disease of the brain is concerned with blockage or cessation of blood flow through the smaller arteries of the brain. If it results in temporary blockage of the blood flow to the brain tissue, it is called TIA or Transient Ischemic Attack that usually resolves within 24hours. it is also called mini stroke.
If this blockage persists for more than 24 hours, it is called stroke. it leads to permanent damage to the effected brain tissue resulting in los of function assigned to that area of the brain.
If repeated mini strokes or TIAs occur, this lead to multiinfarct dementia.
Uncontrolled high blood pressure and diabetes are two major risk factors apart from high cholesterol, genetics etc
Once arae of the brain is damaged by stroke, it is not possibe to reverse it.
But such attacks can be prevented by having good controll over the blood pressure, good control of the diabetes, by taking aspirin or aggrenox etc if not contraindicated.
Here is a nice link from where you can get good enough information in simple terms.