Increased fluorine-18 2-fluoro-2-deoxy-D-glucose (FDG) uptake in childhood CNS tumors is correlated with malignancy grade: A study with FDG positron emission tomography/magnetic resonance imaging coregistration and image fusion

Purpose: Positron emission tomography (PET) has been used in grading of CNS tumors in adults, whereas studies of children have been limited. Patients and Methods: Nineteen boys and 19 girls (median age, 8 years) with primary CNS tumors were studied prospectively by fluorine-18 2-fluoro-2-deoxy-D-glucose (FDG) PET with (n = 16) or without (n = 22) H₂¹⁵O-PET before therapy. Image processing included coregistration to magnetic resonance imaging (MRI) in all patients. The FDG uptake in tumors was semiquantitatively calculated by a region-of-interest-based tumor hotspot/brain index. Eight tumors without histologic confirmation were classified as WHO grade 1 based on location, MRI, and clinical course (22 to 42 months). Results: Four grade 4 tumors had a mean index of 4.27 ± 0.5, four grade 3 tumors had a mean index of 2.47 ± 1.07, 10 grade 2 tumors had a mean index of 1.34 ± 0.73, and eight of 12 grade 1 tumors had a mean index of -0.31 ± 0.59. Eight patients with no histologic confirmation had a mean index of 1.04. For these 34 tumors, FDG uptake was positively correlated with malignancy grading (n = 34; r = 0.72; P < .01), as for the 26 histologically classified tumors (n = 26; r = 0.89; P < .01). The choroid plexus papilloma (n = 1) and the pilocytic astrocytomas (n = 3) had a mean index of 3.26 (n = 38; r = 0.57; P < .01). H₂¹⁵O-uptake showed no correlation with malignancy. Digitally performed PET/MRI coregistration increased information on tumor characterization in 90% of cases. Conclusion: FDG PET of the brain with MRI coregistration can be used to obtain a more specific diagnosis with respect to malignancy grading. Improved PET/MRI imaging of the benign hypermetabolic tumors is needed to optimize clinical use.