# Cerebral blood flow, autoregulation and vascular reactivity in normal pressure hydrocephalus: a systematic review

## TL;DR

This review examines how blood flow and vascular reactivity in the brain relate to normal pressure hydrocephalus and its treatment outcomes.

## Contribution

The study updates a prior review and evaluates the predictive value of cerebrovascular reactivity over baseline blood flow in NPH.

## Key findings

- Reduced global and regional cerebral blood flow is common in NPH but does not predict shunt response.
- Cerebrovascular reactivity shows greater promise as a predictor of clinical improvement after CSF drainage.
- Combining assessments of haemodynamic reserve and CSF dynamics may improve outcome prediction in NPH.

## Abstract

Normal pressure hydrocephalus (NPH) is one of the few remediable causes of decline in gait and cognitive function in the ageing population. The roles of the cerebral circulation including haemodynamic reserve and cardiovascular co-morbidity in the pathogenesis, management and prognostication of NPH remain ill-defined. In this systematic review, we have updated Owler & Pickard’s review of 2001 to examine whether:

global/regional Cerebral Blood Flow (CBF) changes are specific to NPH, appropriately coupled to cerebral metabolism and/or reflect cerebral ischaemia; changes in global/regional CBF are predictive of outcome after CSF drainage; global and regional cerebrovascular autoregulation and reactivity are more sensitive predictors of outcome after CSF drainage than baseline regional CBF (rCBF); changes in global or regional CBF a cause or effect (‘chicken and the egg’) of NPH; a trial is warranted that combines assessments of haemodynamic reserve, CSF outflow resistance and response to temporary CSF drainage.

We have systematically reviewed studies from 2000–2024 assessing CBF, autoregulation, and cerebrovascular reactivity (CVR) in adult NPH. Global and regional CBF were consistently reduced in NPH, particularly in periventricular white matter and deep grey matter, but these reductions were not predictive of shunt response. CVR varied from impaired to preserved and showed greater promise as a predictor of clinical improvement after CSF drainage or shunting. Methodological heterogeneity and small sample sizes limited meta-analysis. The interplay between CBF, CSF dynamics, and brain biomechanics remains complex, with evidence suggesting that impaired haemodynamic reserve may precede irreversible tissue damage.

Baseline rCBF and borderline ischaemia reflect NPH networks but do not predict shunt response. CVR impairment does. It is suggested that randomised controlled trials be used to assess the predictive accuracy of combining the response of temporary CSF drainage with changes in CVR.