Transcranial doppler ultrasonography in normal pressure hydrocephalus: a systematic review and exploratory meta-analysis of diagnostic, prognostic, and monitoring roles.

Transcranial Doppler (TCD) ultrasonography provides noninvasive measurements of cerebral hemodynamics, but its clinical role in normal pressure hydrocephalus (NPH) remains uncertain. We reviewed its diagnostic, prognostic, and monitoring applications. Five databases were searched through June 10, 2025 for quantitative TCD studies in adults with suspected or confirmed NPH. Study-level eligibility and denominators were reconciled against full reports. Design-specific critical appraisal distinguished physiological association, treatment response, and diagnostic discrimination. Exploratory meta-analyses assessed paired three-month post-shunt changes using restricted maximum likelihood and modified Hartung-Knapp confidence intervals (CIs) for all outcomes. Sixteen direct TCD reports were retained. Potentially overlapping cohorts precluded a reliable total of unique patients. Two shunt studies contributed 21 paired participants. Pooled changes were - 0.14 for pulsatility index (PI; 95% CI - 0.49 to 0.21), - 2.29 cm/s for mean flow velocity (95% CI - 40.37 to 35.79), and 0.75 for Hedges-corrected standardized reactivity change (95% CI - 2.39 to 3.88). The conventional PI interval excluded zero ( - 0.20 to - 0.09), illustrating sensitivity to inference. Physiological associations, small response subgroups, and apparent waveform discrimination did not establish independent clinical utility. TCD can characterize cerebral hemodynamics in NPH, but current evidence does not establish diagnostic thresholds, independent prediction of shunt response, or validated surveillance criteria. Post-shunt physiological changes remain exploratory and do not demonstrate clinical benefit.