Posttraumatic leptomeningeal cysts are very rare, occurring in 0.05–0.6% of skull fractures 1) 2). Usually requires both a widely separated fracture AND a dural tear.
Mean age at injury: < 1 year; over 90% occur before age 3 years 3) (formation may require the presence of a rapidly growing brain 4)), although rare adult cases have been described 5), 6) 7) (a total of 5 cases in the literature as of 1998 8)).