Patients with chronic white matter abnormalities that are not confined to the area supplied by a single penetrating vessel are frequently encountered in clinical practice. The mechanisms leading to this condition are not fully understood and the following are possible: 1. Simultaneous ischemia in multiple parallel penetrating arteries. 2. Increased vascular permeability When the blood pressure in the penetrating artery is very high, leakage or exudation of fluid occurs. The acute onset of this condition is called hypertensive encephalopathy. The disease is characterized by leakage of fluid from the small arteries leading to cerebral edema and petechiae in the brain, sometimes with larger cerebral hemorrhages. When the process is chronic, fluid leakage can lead to gliosis and damage to the white matter and basal ganglia of the brain. Some believe that white matter lesions are due to chronic or recurrent hypertensive disease. This shows the importance of keeping blood pressure stable. 3, Some patients with chronic white matter lesions do not have severe hypertension. In these patients, the intima and intima may be abnormal such that fluid may leak out of the damaged artery even if the blood pressure in the artery is normal. 4. Significantly elevated levels of matrix metalloprotein-9 can disrupt the blood-brain barrier by degrading intravascular tight junction proteins. Elevated levels of metalloprotein in the penetrating vessels may facilitate fluid leakage from these vessels.