A catheter assembly for intracranial treatment of a patient is provided having both outer and inner catheters. The outer catheter has at least one element and defines a lumen in communication with at least one aperture and an opening. The inner catheter is sized to be received within the lumen and includes a passageway in communication with at least one port. The element can be in the form of a contact or sensor. The outer catheter can include an inflatable balloon distal to an element. The balloon is adapted to seal upon inflation the tract created by the outer catheter when inserted into the brain. The outer catheter may have a flexible channel extending outward from the body of the catheter that permits the inner catheter to be inserted into the body through the channel. The inner catheter is preferably configured for removable engagement to a tapered fitting on the outer catheter.