Only complications leading to reoperation were counted and grouped into (1) mechanical: most commonly, shunt obstruction or displacement; (2) infections: intraabdominal, skin or CNS infections; (3) subdural hematomas (evacuation of hematoma and/or ligation of shunt), and (4) other or not specified. All reoperations were registered separately even if they referred to the same complication; for instance, management of an intraabdominal infection, first by externalization of the distal catheter and later by removal of the whole shunt, would count as two operations. However, shunt insertions performed after ventriculostomy, reinsertions after earlier shunt removals, and reopening of temporarily ligated shunts were not considered related to new complications and, therefore, not registered in this study.