Increased free interstitial fluid in the normal appearing brain in idiopathic normal pressure and post-hemorrhagic hydrocephalus despite unchanged choroid plexus size.

Authors

Marc Hohenhaus, Horst Urbach, Nils Schröter, Marco Reisert, Theo Demerath, Mukesch J Shah, Jonas A Hosp, Jürgen Beck, Alexander Rau

Published in

Neuroradiology. Jul 07, 2026. Epub Jul 07, 2026.

Abstract

Adult hydrocephalus entities that require shunting may share downstream tissue-level consequences through disturbed CSF dynamics. We compared choroid plexus (ChP) size and diffusion-derived free interstitial fluid fraction (V-CSF) in normal-appearing white matter (NAWM) and gray matter among patients with idiopathic normal pressure hydrocephalus (iNPH), post-subarachnoid hemorrhage (SAH) communicating hydrocephalus, and healthy controls.
We retrospectively identified patients who underwent CSF shunting and high-resolution 3D T1-weighted MRI and multishell diffusion MRI. Diffusion data were processed using a three-compartment Bayesian model to estimate V-CSF. T1-weighted images were segmented into tissue classes and white matter lesions were manually delineated and excluded to derive NAWM masks. Group differences in V-CSF (NAWM, gray matter) and ChP volume were tested using ANCOVA with age as covariate and Tukey post-hoc testing.
The cohort included 22 iNPH patients, 7 post-SAH hydrocephalus patients, and 31 healthy controls. V-CSF was higher in iNPH (0.12 ± 0.01) and post-SAH (0.11 ± 0.01) compared with controls (0.10 ± 0.01; p < 0.001 and p = 0.002), with no difference between iNPH and post-SAH (p = 0.76). Gray matter V-CSF was higher in iNPH (0.21 ± 0.04) than controls (0.11 ± 0.02; p = 0.045), while post-SAH did not differ from iNPH (p = 0.54) or controls (p = 0.76). ChP size did not differ across all groups after age adjustment (p = 0.29).
Shunt-requiring iNPH and post-SAH communicating hydrocephalus show increased free interstitial fluid in NAWM, with additional gray matter involvement in iNPH, while ChP size is unchanged. This pattern supports impaired clearance and widespread free interstitial fluid accumulation while no ChP enlargement as indirect marker of CSF overproduction was found.

PMID:
42412189
Bibliographic data and abstract were imported from PubMed on 07 Jul 2026.

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