“…3,7,11) Subdural hygromas caused by arachnoid cyst are not always unilateral, and bilateral hygromas can transform into bilateral CSDH. 11,14,16) The pathogenesis of evolution of subdural hygromas into CSDH 9,16,19) and the mechanism of hematoma enlargement has been discussed, mostly in adult cases without arachnoid cyst. 4,6,11,12,[20][21][22] CSF in the subdural space forms a fibrous outer membrane under the dura mater.…”