Investigators at the Massachusetts General Hospital, Boston, MA, and Universitat Autonoma de Barcelona, Spain, assessed the prevalence and characteristics of arachnoid cysts in a cohort of 220 patients with tuberous sclerosis complex (TSC). A review of brain MRIs found arachnoid cysts in 12 (5.5%) TSC patients compared to 0.5% in the general population. Ten (83.3%) were males. Four patients (33.3%) had also autosomal dominant polycystic kidney disease (ADPKD) due to a contiguous deletion of the TSC2-PKD1 genes. Three patients (25%) had 2 or more arachnoid cysts, of whom 2 also had ADPKD. One patient with an arachnoid cyst did not have tubers, subependymal nodules or white matter migration lines. 
COMMENTARY. Arachnoid cysts may be part of the clinical spectrum of TSC. They originate from the cranial leptomeninges and dysfunction of the neural crest. Most are sporadic but some are familial, suggesting a genetic factor. The location is predominantly in the left temporal fossa but some are bilateral. Arachnoid cysts are also reported in neurofibromatosis type 1 , and Sturge-Weber syndrome .