PROTON MAGNETIC-RESONANCE SPECTROSCOPIC IMAGING OF PEDIATRIC LOW-GRADE ASTROCYTOMAS

Despite their uniform histologic appearance, pediatric low-grade astro cytomas (LGA) often exhibit a rather unpredictable clinical course. It is presently unclear whether certain specific genetic, immunologic an d/or metabolic features underlie these observed variations. In order t o address this question we examined the tumor distribution of choline compounds (Cho), creatine (Cr) and N-acetyl aspartate (NAA) in seven c hildren with midline LCA by means of proton magnetic resonance spectro scopy imaging (H-MRSI). Studies were performed with a 1.5 T GE Signa S canner equipped with the standard head coil; nominal voxel size was 7. 5 x 7.5 x 15 mm. This spatial resolution allowed us to select and inde pendently evaluate multiple regions of interest (ROI) in the tumor as well as in areas of normal brain from the same individual. Normalized values of the observed signal intensities demonstrated a lower NAA and Cr content in the tumors than in the surrounding normal brain. Intrat umoral Cho signals were also below normal values in all but one patien t. The average Cho:NAA ratio was consistently higher in the tumor than in the normal brain. However, there was a wide variation (up to fourf old) in the Cho:NAA ratios of different ROIs, even within the same tum or. Our results clearly indicate that pediatric LGAs are metabolically heterogeneous, a feature that may be relevant to the understanding of their variable biologic behavior. Inasmuch as unique metabolic patter ns were observed in some LGAs, we believe that systematic HMRSI studie s of these patients may help define subsets within the group with spec ific therapeutic requirements.