title: Oligodendroglial component complicates the prediction of tumour grading with metabolic imaging.
abstract: OBJECTIVE
  Previous radiological investigations have generally shown the superiority of metabolic imaging in distinguishing high-grade from low-grade glioma, but the presence of an oligodendroglial component may affect the diagnostic accuracy. We investigated the diagnostic accuracy of PET imaging using (11)C-methionine (MET) and (18)F-fluorodeoxyglucose (FDG) in distinguishing high-grade from low-grade glioma, in correlation with the oligodendroglial component.
  
  
  METHODS
  The study population comprised adult patients who underwent preoperative PET imaging using both MET and FDG within 1 week and successful excision of the tumour tissue, which confirmed WHO grade II-IV glioma. We examined the tumour metabolic activity in terms of lesion-to-normal uptake ratios (L/N ratio) in both MET PET and FDG PET images. We assessed the correlation between the imaging results and the histological findings to determine the diagnostic accuracy of receiver operating characteristics (ROC) analysis in detecting high-grade tumours.
  
  
  RESULTS
  We studied 46 patients with glioma (13 low-grade and 33 high-grade), including 26 with an oligodendroglial components. The L/N ratios of the PET images showed significantly higher metabolic activities in high-grade gliomas than in low-grade gliomas for both MET (4.29 ± 1.22 and 2.36 ± 0.72, respectively; p < 0.0001) and FDG (1.72 ± 0.91 and 0.77 ± 0.26, respectively; p = 0.0007) images, although significant overlaps in L/N ratio were observed between high-grade and low-grade gliomas. Excluding the 26 patents with an oligodendroglial component improved the separation for both MET (4.62 ± 1.14 vs. 2.16 ± 0.63; p < 0.001) and FDG (1.76 ± 0.87 vs. 0.71 ± 0.14; p < 0.05) images. The ROC analyses demonstrated the clinical utility of the metabolic radiotracers in distinguishing high-grade from low-grade gliomas, showing similar AUC values for MET (0.91) and FDG (0.92). Excluding the 26 patents with an oligodendroglial component also further improved the diagnostic accuracy for both MET (AUC 0.98), and FDG (AUC 1.00) images. The metabolic radiotracers were significantly correlated with the MIB-1 labelling index (R = 0.52, p < 0.05 for MET; R = 0.52, p < 0.05, for FDG) only in gliomas without an oligodendroglial component.
  
  
  CONCLUSIONS
  For better characterization of gliomas and for risk assessment, the results of metabolic PET imaging should be revised after obtaining the pathological report, because oligodendroglial differentiation may positively influence the substrate metabolism and thus complicated the preoperative evaluation.
authors: Department of Nuclear Medicine, Hokkaido University Graduate School of Medicine, N15 W7, Kita-Ku, Sapporo, 0608638, Hokkaido, Japan, osamumanabe817@med.hokudai.ac.jp.
authors: Osamu
authors: O
authors: Manabe
authors: Naoya
authors: N
authors: Hattori
authors: Shigeru
authors: S
authors: Yamaguchi
authors: Kenji
authors: K
authors: Hirata
authors: Kentaro
authors: K
authors: Kobayashi
authors: Shunsuke
authors: S
authors: Terasaka
authors: Hiroyuki
authors: H
authors: Kobayashi
authors: Hiroaki
authors: H
authors: Motegi
authors: Tohru
authors: T
authors: Shiga
authors: Keiichi
authors: K
authors: Magota
authors: Noriko
authors: N
authors: Oyama-Manabe
authors: Ken-ichi
authors: K
authors: Nishijima
authors: Yuji
authors: Y
authors: Kuge
authors: Nagara
authors: N
authors: Tamaki
mesh_terms: D000328:Adult; D001932:Brain Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology; D005260:Female; D019788:Fluorodeoxyglucose F18; D006801:Humans; D008297:Male; D008715:Methionine; D008875:Middle Aged; D064847:Multimodal Imaging; D009837:Oligodendroglioma / Q000000981:diagnostic imaging* / Q000473:pathology; D049268:Positron-Emission Tomography; D019275:Radiopharmaceuticals; D014057:Tomography, X-Ray Computed
chemical_list: D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18; D008715:Methionine
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