18F-FDG PET of common enhancing malignant brain tumors.

OBJECTIVE: The purpose of our study was to determine whether (18)F-FDG PET can be used to differentiate among common enhancing brain tumors such as lymphoma, high-grade glioma, and metastatic brain tumor.

MATERIALS AND METHODS: We evaluated 34 patients with an enhancing brain tumor on MRI, including seven lymphomas, nine high-grade gliomas, and 18 metastatic tumors. All patients also underwent FDG PET. For PET image analysis, regions of interest were placed over the tumor (T), contralateral cortex (C), and white matter (WM). Average and maximum pixel values were determined at each site. On the basis of these measurements, average and maximum standard uptake values (SUV(avg) and SUV(max)) were calculated, along with activity ratios (T/C(avg), T/WM(avg), T/WM(max), and T/C(max)), and comparisons among lesions were then made.

RESULTS: All parameters were significantly higher for lymphoma than for other tumors (p < 0.01). High-grade gliomas showed significantly higher SUV(avg) and SUV(max) than metastatic tumors (p < 0.05). Other parameters did not differ between lesion types. SUV(max) was the most accurate parameter for distinguishing lymphomas. Using an SUV(max) of 15.0 as a cutoff for diagnosing CNS lymphoma, only one high-grade glioma was found as a false-positive (SUV(max), 18.8).

CONCLUSION: FDG PET may be useful for differentiating common enhancing malignant brain tumors, particularly lymphoma versus high-grade glioma and metastatic tumor. FDG PET can provide useful information for distinguishing between lymphoma and other malignant enhancing brain tumors and is recommended when differential diagnoses are difficult to narrow using MRI alone.