A neurosurgical apparatus includes a guide device and a neurosurgical instrument is disclosed. The guide device includes a tube for insertion into the brain and a head attached to the proximal end of the tube for affixing the guide device to a hole formed in the skull. The head has a passageway therethrough in communication with the bore of the tube such that the bore of the tube and the passageway through the head define an internal channel through which a neurosurgical instrument can be passed into the brain of the subject. The neurosurgical instrument is for insertion to a desired brain target through the internal channel of the guide device. The apparatus includes one or more sealing elements for providing a fluid tight seal between the internal channel of the guide device and the exterior of the neurosurgical instrument to prevent fluid leakage from guide tube.
