Preoperative 11 C-Methionine PET-MRI in Pediatric Infratentorial Tumors.

Purpose MRI is the main imaging modality for pediatric brain tumors, but amino acid PET can provide additional information. Simultaneous PET-MRI acquisition allows to fully assess the tumor and lower the radiation exposure. Although symptomatic posterior fossa tumors are typically resected, the patient management is evolving and will benefit from an improved preoperative tumor characterization. We aimed to explore, in children with newly diagnosed posterior fossa tumor, the complementarity of the information provided by amino acid PET and MRI parameters and the correlation to histopathological results. Patients and Methods Children with a newly diagnosed posterior fossa tumor prospectively underwent a preoperative 11C-methionine (MET) PET-MRI. Images were assessed visually and semiquantitatively. Using correlation, minimum apparent diffusion coefficient (ADCmin) and contrast enhancement were compared with MET SUVmax. The diameter of the enhancing lesions was compared with metabolic tumoral volume. Lesions were classified according to the 2021 World Health Organization (WHO) classification. Results Ten children were included 4 pilocytic astrocytomas, 2 medulloblastomas, 1 ganglioglioma, 1 central nervous system embryonal tumor, and 1 schwannoma. All lesions showed visually increased MET uptake. A negative moderate correlation was found between ADCmin and SUVmax values (r = −0.39). Mean SUVmax was 3.8 (range, 3.3–4.2) in WHO grade 4 versus 2.5 (range, 1.7–3.0) in WHO grade 1 lesions. A positive moderate correlation was found between metabolic tumoral volume and diameter values (r = 0.34). There was no correlation between SUVmax and contrast enhancement intensity (r = −0.15). Conclusions Preoperative 11C-MET PET and MRI could provide complementary information to characterize pediatric infratentorial tumors.