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

Background Unresectable WHO grade II astrocytomas require continuous imaging surveillance. To evaluate whether sodium MRI ( 23 Na-MRI) adds diagnostic value to multiparametric MRI and helps predict progressive disease (PD), patients monitored under a “watchful waiting” strategy were repeatedly examined. Materials and methods 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 23 Na-MRI ( n = 9) at 3 T. At baseline, evaluable 23 Na-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 23 Na-MRI. Data were analyzed using the Cox regression model. Results 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 23 Na signal in tumor tissue at baseline, normalized to sodium phantoms, revealed an HR of 0.91. Conclusion Elevation of rrCBV and rrCBF in the tumor indicates poor prognosis, in line with the literature. 23 Na-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 23 Na-MRI in postoperative aftercare. However, due to the small cohort size with evaluable 23 Na-MRI at baseline, evidence is limited. In future, 23 Na-MRI may help selecting patients for a “watchful waiting” strategy.