Low-grade gliomas and focal cortical developmental malformations: differentiation with proton MR spectroscopy

PURPOSE: To assess proton magnetic resonance (MR) spectroscopy in differentiating between low-grade gliomas and focal cortical developmental malformations (FCDMs). MATERIALS AND METHODS: Eighteen patients with seizures and a cortical brain lesion on MR images were studied with proton MR spectroscopy. A metabolite ratio analysis was performed, and the metabolite signals in the lesion core were compared with those in the contralateral centrum semiovale and in the corresponding brain sites in 18 control subjects to separately obtain the changes in N-acetylaspartate (NAA), choline-containing compounds (Cho), and creatine-phosphocreatine (Cr). Ten patients had a low-grade glioma (three, oligodendrogliomas; three, oligoastrocytomas; three, astrocytomas; and one, pilocytic astrocytoma), and eight had FCDM (five, focal cortical dysplasias and three, dysembryoplastic neuroepithelial tumors). Linear discriminant analysis and Student t test were used for statistical comparisons. RESULTS: Loss of NAA and increase of Cho were more pronounced in low-grade gliomas than in FCDMs (NAA, -72% +/- 15 +/- SD] vs -29% +/- 22, P <.001; Cho, 117% +/- 56 vs 21% +/- 66, P <.01). Changes in NAA and Cho helped differentiate low-grade gliomas from FCDMs, and changes in Cho and Cr helped differentiate astrocytomas from oligodendrogliomas and oligoastrocytomas. Metabolite NAA/Cho and NAA/Cr ratios helped differentiate low-grade gliomas from FCDMs but did not differentiate glioma subtypes. CONCLUSION: MR spectroscopy allows distinction between low-grade gliomas and FCDMs and between low-grade glioma subtypes. Metabolite changes are more informative than are metabolite ratios.