The perivascular spaces are normally microscopic. Even in normal brain some Robin-Virchow spaces are usually seen in the area of substantia innominata at the level of anterior commissure. Many pathologic states result in abnormal dilatation with an increased number of spaces visible on MRI imaging. Dilatation is most commonly associated with anterior abnormalities that arise due to aging, diabetes, hypercholesterolemia, smoking, hypertension and other vascular risk factors. The precise etiology of dilatation is currently unknown.