ventriculocisternostomy

noun

ven·​tric·​u·​lo·​cis·​ter·​nos·​to·​my -ˌsis-tər-ˈnäs-tə-mē 

plural ventriculocisternostomies

: the surgical establishment of a communication between a ventricle of the brain and the subarachnoid space and especially the cisterna magna to drain cerebrospinal fluid especially in hydrocephalus