Metabolic and hemodynamic evaluation of gliomas using positron emission tomography

Positron emission tomography (PET) was used on 16 patients with untreated cerebral gliomas to measure cerebral glucose and oxygen metabolism, oxygen extraction, blood flow, and blood volume. In addition, pH values were obtained for seven cases. Gliomas were later proven by biopsy; two patients had tumors with degrees of malignancy of grade II, two patients had grade III, and 12 patients had grade IV tumors. Compared with homologous gray matter regions in the opposite hemisphere, tumor tissue showed increased blood volume, but decreased oxygen extraction and oxygen metabolism. Compared with grade II tumors, grade IV tumors demonstrated higher blood volumes, but lower relative oxygen extraction and utilization. Tumor blood flow was variable, but was lower in the higher grade tumors. Rates of glucose utilization in tumor, calculated by using individually determined rate constants, were variable, and did not correlate with tumor size or tumor grade. Parietal tumors (n = 6) tended to have higher relative glucose utilization and blood flow, and lower relative oxygen extraction, when compared with frontal tumors (n = 4). Tumor pH differed significantly from the pH in contralateral brain (p less than 0.005); alkalotic pH values were consistently seen. These findings in and around cerebral gliomas studied before intervention differ from the results found in gliomas after exposure to radiation or chemotherapy.