leptomeningeal cystA commonly used synonym for a growing skull fracture, see there.
Patient discussion about leptomeningeal cyst
Q. What is the treatment for an arachnoid cyst? My 15 year old son has just been diagnosed with an arachnoid cyst. What is the treatment? Is an operation necessary?
Q. Is there any problem, if an arachnoid cyst ,2cmx1.5cm size, rostral to cerebellar region left untreated? symptoms: repeated headaches, twitching of muscles, tiredness
Q. info on arachnoid cyst in the right posterior fossa
It's usually congenital (i.e. develops during pregnancy), and even when it cause symptoms they develop slowly.
YOu can read more here (http://en.wikipedia.org/wiki/Arachnoid_cyst)