A sterile implantable device intended to be used with a cerebrospinal fluid (CSF) shunt assembly (e.g., ventriculoperitoneal shunt, lumboperitoneal shunt) for in-line shunt placement to filter particles by size to prevent transmission of cells when draining CSF from the brain. It typically includes a cellulose membrane supported in a stainless steel mesh encased in, e.g., silicone, and has ports for connection to the shunt. It is used when neoplasms are present or suspected in patients who need treatment using a CSF shunt. It may be implanted behind the mastoid air cells to expose its content to radiation when applied.