Do arachnoid cysts grow? A retrospective volumetric study

Objective Arachnoid cysts (ACs) are frequent incidental findings and may be associated with neuropsychiatric symptoms. Usually growth of the ACs with pressure on adjacent brain tissue is regarded as cause of the symptoms. This study was undertaken to identify if and which ACs grow with time. Methods We used a large database of cranial MRIs for a retrospective analysis. Results During a period of 10 years, we collected 166 ACs of 50 persons, mean observational period was 2.5 years. Among these, only larger cysts at the temporal pole, i.e., Galassi II ACs, grew with a rate of 0.3 ml a year ( β = 0.32, SE 0.07, p = 0.003); all other ACs remained constant in size or became smaller. All cysts were clinically silent. Conclusions Most ACs remain constant in size or become smaller. Classification of evidence This study provides Class III evidence that the majority of arachnoid cysts does not grow.