Q: Please explain what is meant by multiple cystic lesion in within an area of demyelination involving bilateral periventricular white matter in brain?

A:Cystic lesion: a diseased area in the brain containing an abnormal collection of fluid within tissue. This fluid collection may be surrounded by a membranous wall. Demyelination: loss of myelin - a fatty sheath surrounding nerve fibres. Myelin insulates nerve fibres and permits them to conduct their electrical messages without cross-talk. Loss of myelin is followed by loss of function in the nerve fibres. Periventricular white matter: The white fibres (nerve fibres together with their insulating myelin sheaths) that surround the normal fluid containing cavities (ventricles) within the brain. Thus the sentence referred to by you above means that the individual has abnormal fluid containing cavities in a part of the brain where the nerve fibres have lost their insulating myelin sheaths. The nervous tissue surrounding the normal fluid containing cavities of the brain have been particularly involved by such disease in this patient.