Impact of a pediatric posterior fossa tumor and its treatments on motor procedural learning

Exploring Memory Systems After Pediatric Posterior Fossa Tumor: From Memory Profile Comparisons in Nonirradiated Versus Irradiated Patients to Episodic Memory Tests Capable of Detecting Radiation-induced Hippocampal Damage

AIMS

Pediatric posterior fossa tumor (PFT) survivors experience long-term cognitive sequelae, including memory disorders, for which irradiation is one of the main risk factors. The aims of the present study were to (1) explore the profile of impairment in episodic, semantic, working and procedural memory systems in irradiated versus nonirradiated PFT survivors, and (2) test whether an autobiographical questionnaire and a two-phase ecological test (Epireal) assessing episodic memory are more sensitive to radiation-induced hippocampal damage than commonly used tests.

MATERIALS AND METHODS

A total of 60 participants (22 irradiated PFT survivors, 17 nonirradiated PFT survivors, and 21 controls) were included in the prospective IMPALA study. They all underwent a broad battery of tests assessing the different memory systems in two 2-day sessions 3 weeks apart. We performed between-groups comparisons and analyzed impairment profiles, using -1.65 SDs as a cut-off. For irradiated patients, correlations were calculated between mean radiation doses to key brain structures involved in memory (hippocampus, cerebellum, and striatum) and corresponding memory scores.

RESULTS

PBT survivors performed significantly more poorly than controls (p < 0.001) on conventional tests of episodic, semantic and working memory: 64% of irradiated patients and 35% of nonirradiated patients had a deficit in at least two memory systems, with episodic memory impairment being more specific to the irradiated group. Epireal had a larger effect size than the other episodic memory tests, allowing us to detect deficits in a further 18% of irradiated patients. These deficits were correlated with the mean radiation dose to the left hippocampus.

CONCLUSION

Memory impairment is a frequent long-term cognitive sequela in PFT survivors, especially after radiation therapy. New ecological tests of episodic memory that are more sensitive to radiation-induced deficits than conventional tests could yield specific markers of the toxicity of medial temporal lobe irradiation.

The long-term impact of irradiation on functional connectivity in brain circuits involved in memory processes after pediatric posterior fossa tumor

PURPOSE

Memory is one of the main specific cognitive domains impaired with attention and processing speed after a pediatric brain tumor. This work explored the long-term impact of radiotherapy in children with posterior fossa tumor (PFT) on brain connectivity in neural circuits involved in memory using resting-state functional magnetic resonance imaging (rs-fMRI).

METHODS

A total of 20 irradiated and 15 non-irradiated PFT survivors, and 21 healthy controls, prospectively included in the IMPALA study (NCT04324450), performed memory tests assessing episodic, procedural, and working memories and were subjected to an rs-fMRI. We manually contoured main structures involved in memory to explore connectivity at rest in a seed-to-voxel analysis. The groups were compared and differences in connectivity were correlated with behavioral scores and irradiation doses.

RESULTS

The performance of all mnesic tasks was lower in PFT survivors with a greater alteration in working and episodic memory in irradiated patients. Irradiated survivors had atypical connectivities in all memory circuits compared to controls and in cortico-caudate and cortico-cerebellar circuits compared to non-irradiated survivors. Non-irradiated survivors had only atypical connectivities in the cortico-cerebellar circuits compared to controls. In irradiated survivors, atypical connectivities in cortico-hippocampal circuits were linked with episodic memory scores and dose of irradiation to the left hippocampus and in cortico-striatal circuits with procedural memory scores and dose of irradiation to the striatum.

CONCLUSION

The results of this study highlight that irradiation has a long-term impact on brain connectivity in brain circuits involved in memory after pediatric PFT with a specific radiation-dose effect in supratentorial structures.

A Prospective Study of Arterial Spin Labelling in Paediatric Posterior Fossa Tumour Survivors: A Correlation with Neurocognitive Impairment

AIMS

Posterior fossa tumours (PFTs), which account for two-thirds of paediatric brain tumours, are successfully treated in about 70% of patients, but most survivors experience long-term cognitive impairment. We evaluated arterial spin labelling (ASL), a common, non-invasive magnetic resonance imaging (MRI) technique, as a biomarker of cognitive impairment in a paediatric PFT survivor population.

MATERIALS AND METHODS

Sixty participants were prospectively analysed. PFT survivors were at least 5 years post-treatment and had been treated as appropriate for their age and type of tumour. Group 1 had received radiotherapy and Group 2 had not. Group 3 were healthy controls matched to Group 1 for age, sex and handedness. All participants underwent cognitive assessment and multimodal MRI, including an ASL perfusion sequence. We used semi-quantitative ASL methods to assess differences in mean perfusion in the thalamus, caudate, putamen and hippocampus.

RESULTS

Statistically, no significant associations between cognitive data and radiation doses were identified. Compared with healthy controls, Group 1 patients had significantly lower overall mean perfusion values (20-30% lower, depending on the cerebral structure) and Group 2 had slightly lower mean perfusion values (5-10% lower). Perfusion values did not correlate with total prescribed irradiation doses nor with doses received by different cerebral structures. Episodic and semantic memory test scores were significantly lower in Group 1 and correlated with lower mean absolute perfusion values in the hippocampus (P < 0.04).

CONCLUSIONS

These preliminary results indicate that radiotherapy affects the perfusion of specific cerebral structures and identify perfusion as a potential biomarker of hippocampus-dependent memory deficit.