Background
Normal pressure hydrocephalus (NPH) occurs when the brain ventricles expand, causing a triad of gait, cognitive, and urinary impairment. It can occur after a clear brain injury such as trauma, but can also occur without a clear cause (termed idiopathic, or iNPH). Non‐randomised studies have shown a benefit from surgically diverting ventricular fluid to an area of lower pressure by cerebrospinal fluid (CSF)‐shunting in iNPH, but historically there have been limited randomised controlled trial (RCT) data to confirm this.

Objectives
To determine the effect of CSF‐shunting versus no CSF‐shunting in people with iNPH and the frequency of adverse effects of CSF‐shunting in iNPH.

Search methods
We searched the Cochrane Dementia and Cognitive Improvement Group's register, Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE (Ovid SP), Embase (Ovid SP), PsycINFO (Ovid SP), CINAHL (EBSCOhost), Web of Science Core Collection (Clarivate), LILACS (BIREME), ClinicalTrials.gov, and the World Health Organization International Clinical Trials Registry Platform on 15 February 2023.

Selection criteria
We included only RCTs of people who had symptoms of gait, cognitive, or urinary impairment with communicating hydrocephalus (Evans index of > 0.3) and normal CSF pressure. Control groups included those with no CSF shunts or those with CSF shunts that were in 'inactive' mode.

Data collection and analysis
We used standard Cochrane methodological procedures. Where necessary, we contacted study authors requesting data not provided in the papers. We assessed the overall certainty of the evidence using GRADE.

Main results
We included four RCTs, of which three were combined in a meta‐analysis. The four RCTs included 140 participants (73 with immediate CSF‐shunting and 67 controls who had delayed CSF‐shunting) with an average age of 75 years. Risk of bias was low in all parallel‐group outcomes evaluated apart from gait speed, cognitive function (general cognition and Symbol Digit Test) (some concerns) and adverse events, which were not blind‐assessed. CSF‐shunting probably improves gait speed at less than six months post‐surgery (standardised mean difference (SMD) 0.62, 95% confidence interval (CI) 0.24 to 0.99; 3 studies, 116 participants; moderate‐certainty evidence). CSF‐shunting may improve qualitative gait function at less than six months post‐surgery by an uncertain amount (1 study, 88 participants; low‐certainty evidence). CSF‐shunting probably results in a large reduction of disability at less than six months post‐surgery (risk ratio 2.08, 95% CI 1.31 to 3.31; 3 studies, 118 participants; moderate‐certainty evidence). The evidence is very uncertain about the effect of CSF‐shunting on cognitive function at less than six months post‐CSF‐shunt surgery (SMD 0.35, 95% CI −0.04 to 0.74; 2 studies, 104 participants; very low‐certainty evidence). The evidence is also very uncertain about the effect of CSF‐shunt surgery on adverse events (1 study, 88 participants; very low‐certainty evidence). There were no data regarding the effect of CSF‐shunting on quality of life.

Authors' conclusions
We found moderate‐certainty evidence that CSF‐shunting likely improves gait speed and disability in iNPH in the relative short term. The evidence is very uncertain regarding cognition and adverse events. There were no longer‐term RCT data for any of our prespecified outcomes. More studies are required to improve the certainty of these findings. In addition, more information is required regarding patient ethnicity and the effect of CSF‐shunting on quality of life.