an operation in which a *shunt is created between the lateral *ventricle of the brain and the *cisterna magna to bypass a block of the cerebral *aqueduct and thus relieve *hydrocephalus. Originally this was achieved by means of an external indwelling catheter, but later techniques use an internal catheter, which reduces the risk of septic complications. [A. Torkildsen (20th century), Norwegian neurosurgeon]