Preoperative and postoperative¹H-MR spectroscopy changes in frontal deep white matter and the thalamus in idiopathic normal pressure hydrocephalus

Background

In a previous study we found significantly decreased N-acetyl aspartate (NAA) and total N-acetyl (tNA) groups in the thalamus of patients with idiopathic normal pressure hydrocephalus (iNPH) compared with healthy individuals (HI). No significant difference between the groups could be found in the frontal deep white matter (FDWM).

Objective

The primary aim of this study was to investigate if these metabolites in the thalamus were normalised after shunt surgery. The secondary aim was to investigate postoperative metabolic changes in FDWM.

Subjects and methods

Fourteen patients with iNPH, mean age 74 years, and 15 HI, also mean age 74 years, were examined. Assessment of a motor score (MOSs) was performed before and after shunt surgery. Absolute quantitative ¹H-MR spectroscopy (1.5 T, volumes of interest 2.5–3 ml) was performed on the patients in the FDWM and in the thalamus, before and 3 months after shunt surgery, and also once on the HI. The following metabolites were analysed: tNA, NAA, total creatine, total choline (tCho), myo-inositol (mIns), glutamate and lactate concentrations. MRI volumetric calculations of the lateral ventricles were also performed.

Results

At 3 months postoperatively, we found no significant changes of tNA or NAA in the thalamus. In contrast, in the FDWM, there was a significant increase of tCho (p=0.01) and a borderline significant decrease of mIns (p=0.06). 12/14 patients were shunt responders (motor function). Median reduction of the lateral ventricle was 16%. A weak correlation between MOS and ventricular reduction was seen.

Conclusions

Normalisation of thalamic tNA and NAA could not be detected postoperatively. The increased tCho and decreased mIns in the FDWM postoperatively might relate to clinical improvement.