Differential diagnosis between radiation necrosis and glioma progression using sequential proton magnetic resonance spectroscopy and methionine positron emission tomography

Differential diagnosis between radiation necrosis and tumor recurrence is important in the clinical management of glioma. Multi-modality imaging including proton magnetic resonance spectroscopy (¹H-MRS) and positron emission tomography (PET) with L-[methyl-¹¹C]methionine (MET) was evaluated. Eighteen patients underwent sequential ¹H-MRS and MET-PET. The expressions of metabolites including choline-containing compounds (Cho), creatine phosphate (Cre), and lactate (Lac) were calculated as the ratios of Cho to Cre (Cho/Cre) and Lac to Cho (Lac/Cho). The uptake of MET was determined as the ratio of the lesion to the contralateral reference region (L/R). The final diagnoses were determined by histological examination and/or follow-up MR imaging and clinical course. The Lac/Cho ratio was 0.63 ± 0.25 (mean ± standard deviation) in recurrence (7 cases) and 2.35 ± 1.81 in necrosis (11 cases). The Lac/Cho ratio was significantly different between the two groups (p < 0.01). Consecutive investigation of ¹H-MRS revealed temporary elevation of Cho in 4 of 9 cases of necrosis, which could be identified as false positive findings for recurrence. Including those cases, MET-PET demonstrated significant difference in the L/R ratio between the two groups (2.18 ± 0.42 vs. 1.49 ± 0.35, p < 0.01). According to a 2 x 2 factorial table analysis, the borderline values of Lac/Cho and L/R to differentiate recurrence from necrosis were 1.05 and 2.00, respectively. ¹H-MRS is reliable and accessible for the differentiation of recurrence and necrosis, although the temporary elevation of Cho in the course of necrosis should be recognized. Additional MET-PET imaging can establish the diagnosis.