Increased dimensions of the Virchow-Robin spaces (also known as perivascular spaces), which surround the walls of vessels as they course from the subarachnoid space through the brain parenchyma. Perivascular spaces are commonly microscopic, and not visible on conventional neuroimaging. This term refers to an increase of size of these spaces such that they are visible on neuroimaging (usually magnetic resonance imaging). The dilatations are regular cavities that always contain a patent artery. The phenotype is Dilation of Virchow-Robin spaces (HP_0012520, a Human Phenotype Ontology entry). Also known as: Dilated Virchow-Robin spaces, Perivascular spaces.