Objectives: White matter changes as measured by diffusion tensor imaging (DTI) typically reflect the functionality of individual tracts. The aim of this study was to investigate the changes of DTI parameters in the most significant tracts and regions before and after implantation of the shunt system in idiopathic normal pressure hydrocephalus (iNPH) patients along with the evaluation of the relationship between DTI parameters and clinical improvement.

Methods: Between 2017 and 2022, patients with probable iNPH underwent prospective preoperative magnetic resonance imaging (MRI) and comprehensive clinical workup. Patients with clinical symptoms of iNPH, positive result on lumbar infusion test (LIT) and/or gait improvement after 120-hour lumbar drainage (LD) were diagnosed with iNPH and underwent shunt-placement surgery. Fractional anisotropy (FA) and mean diffusivity () values for individual regions of interest were extracted from preoperative and postoperative MRI. These FA and values were correlated with the clinical picture of individual patients and preoperative DTI predictors of LIT response were studied.

Results: A total of 32 patients (73.59 ± 4.59 years) with definite iNPH were analyzed. Preoperative DTI characteristics of internal capsule and corona radiata correlated with the long-term improvement in the Dutch Gait Scale postoperatively (all p<0.036). Cognitive domain improvement after surgery in memory and psychomotor speed correlated with preoperative DTI values of cingulate gyrus (p=0.050), uncinate fasciculus (p=0.029), superior longitudinal fasciculus (p=0.020) or corpus callosum (all p<0.045). All patients with negative LIT (10%) clinically and radiologically improved after surgery. FA value of the posterior limb of the internal capsule with AUC of 0.90 (95% confidence interval, CI, 0.78–1.00) was the best predictor of the LIT result.

Conclusion: DTI characteristics of white matter regions reflect clinical improvement after shunt surgery in iNPH patients in terms of both gait and cognitive impairments. Negative LIT should not directly exclude patients from shunting without additional testing. iNPH patients tend to improve towards physiological FA and values, thus further accentuating the benefit of shunt surgery in both clinical and radiological pictures.