LAUSR

BACKGROUND Perivascular spaces (PVS), also known as Virchow-Robin spaces, are pial-lined, interstitial fluid-filled structures in the brain that accompany cerebral vessels as they penetrate the cerebral substance. In healthy individuals, a PVS diameter of <2 mm is considered normal and can typically be seen within the white matter on magnetic resonance imaging (MRI). When PVS dilate, they are considered benign lesions and are associated with aging and other risk factors. These dilated PVS can cause neurologic symptoms, depending on their size and location. Symptomatic, massive enlargement of PVS are referred to as "giant" or "tumefactive" PVS; these are extremely rare and require neurosurgical intervention. CASE DESCRIPTION We present a rare case of giant tumefactive PVS (GTPVS) associated with hydrocephalus in a female patient who presented with progressive headache for 6 months. The patient was found to have giant tumefactive dilatation of PVS involving the right midbrain, with extension to the pons and thalamus, and with supratentorial moderate hydrocephalus. She was treated with cerebrospinal fluid diversion alone. CONCLUSIONS PVS are found on MRI in healthy people; rarely, they may dilate and cause neurologic symptoms. GTPVS are rare and can be misdiagnosed as central nervous system tumors; however, their imaging characteristics facilitate diagnosis. It has been postulated that these expanding PVS are due to defects in the drainage of interstitial fluid, where it enters into the ventricular system, and they are not the result of increased intraventricular pressure. We hypothesize that this may have been the case for the patient in our study, as the GTPVS collapsed following the insertion of a ventriculoperitoneal shunt. However, more recent literature provides evidence to support the idea that hydrocephalus is the consequence, and not the cause, of aqueduct compression by the lesion.