# Added value of sodium MRI in multiparametric MRI for WHO grade II astrocytoma surveillance during “watchful waiting”: initial experience

## TL;DR

This study explores whether sodium MRI adds value to standard imaging for monitoring low-grade brain tumors during watchful waiting.

## Contribution

The study is among the first to evaluate sodium MRI's role in predicting tumor progression in WHO grade II astrocytomas.

## Key findings

- Elevated cerebral blood volume and flow in tumors correlate with poor prognosis.
- Higher baseline sodium MRI signal in some tumors was associated with better outcomes.
- Sodium MRI shows potential for aiding surveillance in treatment-naïve astrocytomas.

## Abstract

Unresectable WHO grade II astrocytomas require continuous imaging surveillance. To evaluate whether sodium MRI (23Na-MRI) adds diagnostic value to multiparametric MRI and helps predict progressive disease (PD), patients monitored under a “watchful waiting” strategy were repeatedly examined.

Overall, 18 patients with biopsy-proven WHO grade II astrocytoma (10 female, mean age 42 ± 15 years) were prospectively included after baseline imaging. The imaging protocol comprised morphological MRI (T2 TSE, T2 FLAIR, pre- and post-contrast T1 SE), DSC perfusion MRI (n = 17), and 23Na-MRI (n = 9) at 3 T. At baseline, evaluable 23Na-MRI was available for six patients. The Response Assessment in Neuro-Oncology criteria were used to define PD. Semiquantitative ROI analysis was performed on DSC- and 23Na-MRI. Data were analyzed using the Cox regression model.

In 14 patients (78%), PD was found after a mean of 420 ± 354 days. For the endpoint time to progression, univariate Cox regression revealed a hazard ratio (HR) of 1.39 for relative regional cerebral blood volume (rrCBV) in the tumor at baseline, and an HR of 1.29 for relative regional cerebral blood flow (rrCBF) at baseline. The 23Na signal in tumor tissue at baseline, normalized to sodium phantoms, revealed an HR of 0.91.

Elevation of rrCBV and rrCBF in the tumor indicates poor prognosis, in line with the literature. 23Na-MRI can be used for WHO grade II astrocytoma surveillance. In some treatment-naïve WHO grade II astrocytomas, an initially high sodium signal seems to be prognostically favorable, contrary to the literature on 23Na-MRI in postoperative aftercare. However, due to the small cohort size with evaluable 23Na-MRI at baseline, evidence is limited. In future, 23Na-MRI may help selecting patients for a “watchful waiting” strategy.