Abstract: A catheter assembly comprising a catheter having a lumen and characterized by a flexible distal extremity. The assembly further comprises a bolt having a threaded distal extremity for threading into an opening in the skull in sterile relation. The bolt includes an elongated chamber extending between its distal extremity and a threaded proximal extremity of the bolt. The catheter is disposed through the bolt chamber, and includes an opening from the lumen to the exterior of its flexible distal extremity. A clamp is threaded onto the catheter proximal extremity and is operative to forcibly engage the catheter and constrain it against movement relative to the bolt to thereby maintain a predetermined depth of insertion of the catheter into the skull.