Asymptomatic supratentorial arachnoid cyst and symptomatic demyelination plaques: which one needs treatment?

Intracranial arachnoid cysts are rare but the widespread use of brain imaging has disclosed many asymptomatic cysts. The authors report the case of a 37-year-old woman who presented with features suggestive of relapsing-remitting multiple sclerosis (MS). Her brain MRI revealed a moderately large arachnoid cyst in the right frontal area in addition to the periventricular plaques of MS. The cyst was an incidental imaging finding and the patient was asymptomatic prior to the development of MS.