1. Patient undergoing elective craniotomy/craniectomy for pathological processes (such as benign and malignant tumors, vascular malformation) in the posterior fossa or in the supratentorial region and who are demonstrated to have persistent CSF leakage following suture closure of the dural incision. CSF leakage will be evaluated during a period of Valsalva of 10-20 cm of H20 for 5-10 seconds. If a spontaneous leak is apparent immediately after dural closure, no Valsalva will be performed.