I Can't See Straight

Perivascular spaces, otherwise known as Virchow-Robin spaces are normal anatomic structures typically less than 5mm in diameter. Small enlargements of the spaces are not at all infrequent, being detectable on MRI in up to 60% of healthy individuals. They are in direct communication with the subpial space, separated from the subarachnoid space by a single layer of pia mater. There has been postulated to be a communication with the lymphatic system, draining the head and neck. The teleologic purpose of the Virchow-Robin spaces has been debated, including suggestion of involvement in immune modulation, providing an entry route for macrophages. Pathologically they may be a potential route of dissemination for intracranial pyogenic infection. Characteristically on MRI scan they are iso-intense to CSF without enhancement, and the small typical ones follow the path of penetrating cerebral arteries, particularly in the area of the basal ganglion. When grossly dilated they tend to most frequently involve the mesencephalon, as in our patient. They most commonly follow the paramedian mesocephalo-thalamic artery. While the majority of these are asymptomatic, when they enlarge sufficiently, they may produce mass effect. Most of the surgical approaches to these depend on relieving that mass effect. The recent introduction of endoscopic surgery can easily decompress some of the cystic spaces if they appear to be producing compression. In this particular case, it was unclear that any surgical intervention was likely to improve the patient's findings.