In this study, the investigators will prospectively investigate if ultrasound guidance may raise the number of well placed ventricular catheters and may reduce the number of undesirable side effects. In this study the correct catheter position is defined when the catheter tip is located in the ipsilateral lateral ventricle (to the burrhole) anterior of the foramen of monroi and will be assessed by cranial computer tomography after operation. The CT Scans will be evaluated by an independent expert rater, blinded for the procedure type.