C-11 METHIONINE PET FOR DIFFERENTIAL-DIAGNOSIS OF LOW-GRADE GLIOMAS

Management of low-grade gliomas continues to be a challenging task, be cause CT and MRI do not always differentiate from nontumoral lesions. Furthermore, tumor extent; and aggressiveness often remain unclear bec ause of a lack of contrast enhancement. Previous studies indicated tha t large neutral amino acid tracers accumulate in most brain tumors, in cluding low-grade gliomas, probably because of changes of endothelial and blood-brain barrier function. We describe C-11-methionine uptake m easured with PET in a series of 196 consecutive patients, most of whom were studied because of suspected low-grade gliomas. Uptake in the mo st active lesion area, relative to contralateral side, was significant ly different among high-grade gliomas, low-grade gliomas, and chronic or subacute nontumoral lesions, and this difference was independent fr om contrast enhancement in CT or MRI. Corticosteroids had no significa nt effect on methionine uptake in low-grade gliomas but reduced uptake moderately in high-grade gliomas. Differentiation between gliomas and nontumoral lesions by a simple threshold was correct in 79%. Recurren t or residual tumors had a higher uptake than primary gliomas. In conc lusion, the high sensitivity of C-11-methionine uptake for functional endothelial or blood-brain barrier changes suggests that this tracer i s particularly useful for evaluation and follow-up of low-grade glioma s.