Session Item

Posterior fossa tumors (PFT) represent two thirds of brain tumors in children. Although progress in treatment has improved survival rates over the past few years, long-term impairments in memory are frequent. The hippocampi, cerebellum and striatum play a role respectively in episodic and semantic, working and procedural memory. They are affected not only by the location of the tumor itself and the surgery, but also by the complementary treatments, particularly radiotherapy (RT). The aim of this work was to investigate new MRI biomarkers of cognition decline using perfusion MRI with arterial spin labelling (ASL) and 3D MRI spectroscopy (MRSI).

Sixty participants, divided into 3 groups, were included in this prospective IMPALA study (NCT04324450): the first 2 groups included patients considered to be cured and completed treatment at least 5 years earlier, either with RT (G1: 22 patients) or without RT (G2: 17 patients), G3 included healthy subjects matched with G1 for age, sex, and handedness. All participants performed neuropsychological tests, including an assessment of the main memory systems and undergo multimodal MRI (Philips Achieva dStream 3.0 T). After image post-processing, metabolite values (choline (Cho), N-acetylaspartate (NAA), creatine (Cr)) were extracted in cerebellum and mean perfusion values were extracted from ASL perfusion weighted maps. Mean and maximum doses at hippocampus, caudate nucleus, putamen, thalamus and cerebellum were collected from the initial dosimetry plan. The comparisons between groups were made with the Chi-square, Fisher's exact, or Kruskal Wallis tests. Correlations were evaluated using Spearman's rank coefficient.

Median values of Cho, Cr, NAA and ratio of NAA to the sum of metabolites were significantly lower in G1 &G2 compared to healthy subjects (P<0.05). Scores of working and procedural memories tests were significantly lower in G1& G2 (P<0.004) and correlated to median and maximum values of Cho and NAA (0.28< r <0.49, p<0.04).
For others brain structures, statistically significant differences in perfusion values were found between G1 & G3 (P<0.05). Scores of episodic and semantic memories tests were significantly lower in G1 and correlated with mean absolute values of perfusion in hippocampi (0.30< r <0.35, p<0.04).

No significant differences were found between G1 & G2 (MRSI or ASL values) or between G2 & G3 (ASL values).

Neither MRSI nor perfusion values were correlated to total dose or doses in structures.

In this study, we showed changes in cerebellar metabolic values in PFT survivors and in perfusion values in other brain structures in the RT group. These values have been correlated with memory deficits suggesting that it could be used as a biomarker of cognitive decline, but this will require validation on a larger sample . Further statistical analysis, including structural, diffusion (DTI), and functional (rs-fMRI) imaging results, is ongoing.