Metabolic characterization of brainstem glioma in children according to 11C-methionine PET/CT data: a retrospective study

INTRODUCTION : One of the main difficulties in prognosis and treatment planning in children with brainstem glioma is rare histological verification of the diagnosis, which prompts increased attention to non-invasive diagnostics using neuroimaging. OBJECTIVE : To study the metabolic characteristics of brainstem and thalamic tumors in children using PET/CT with 11 Cmethionine (Met) in association with MRI results. MATERIALS AND METHODS : The study included the results of Met PET/CT in 63 children aged 3 to 18 with brainstem gliomas who underwent contrast-enhanced MRI (CE) and 11 C-methionine PET/CT before treatment. The analysis was performed on fused PET and MRI images and consisted of visual assessment and calculation of Met tumor-to-brain ratio (TBR) and the metabolic tumor volume. RESULTS : Tumors were divided into two groups: diffuse intrinsic pontine gliomas (DIPG) and other gliomas (OG). Significant differences between DIPG and OG were found in lesion size and initial tumor bed. No differences were found in the frequency of tumor contrast enhancement (p=0.21). Met high uptake was observed in 72% of DIPG and in 58% of other gliomas without significant differences (p=0.25), but TBR depended on the reference structure: cerebellum or frontal cortex (p=0.00001). Positive or negative Met tumor uptake, as well as TBR, were not associated with either the tumor type or its localization. The relationship between tumor enhancement and Met uptake pattern was found in DIPG. DISCUSSION : Variability in amino acid transport and metabolism in brainstem tumors did not allow a reliable discrimination between tumor types, which may be due to the similar phenotypic features in DIPG and OG affecting Met uptake. The data obtained are consistent with the results of studies by other groups of authors, which showed that the greatest prognostic value for brainstem tumors is not the histological structure, but the glioma genotype. CONCLUSION : The absence of a specific pattern of methionine transport and metabolism disorders for diffuse midline glioma limits the significance of metabolic biomarkers in the diagnosis and differential diagnosis of brainstem tumors.