Noninvasive histologic grading of solid astrocytomas using proton magnetic resonance spectroscopy

Proton magnetic resonance spectroscopy (1H MRS) constitutes a promising modality to assess intracranial pathology. We present our experience using this method in grading solid brain astrocytomas.

Using a 1.5-Tesla MRI unit, 71 patients with the radiographic diagnosis of astrocytoma were examined. Water-suppressed single-voxel 1H MRS was employed in all of our patients. The concentrations of choline (Cho), N-acetyl-aspartate (NAA), phosphocreatine-creatine (Pcr-Cr), myo-inositol (MI), lactate (Lac), lipids (Lip) as well as the metabolite ratios of Cho/Pcr-Cr, NAA/PCr-Cr and NAA/Cho were calculated. An appropriate surgical biopsy was performed. Standard pathology examination was employed in a double-blinded fashion.

An increased concentration of Cho and decreased concentrations of Pcr-Cr and NAA were detected. The concentrations of Lac, Lip and MI varied inconsistently, even among tumors of the same histologic grade. The Cho/Pcr-Cr ratio was calculated. This ratio was found to be 2.15 +/- 0.26 in 27 patients with astrocytomas grade I and II, 2.78 +/- 0.09 in 18 patients with grade III, and 5.40 +/- 0.16 in 26 patients with grade IV.

The increased concentration of Cho is due to the increased cellularity and a relatively increased number of membranous structures in highly malignant tumors. In abnormal anaerobic metabolic tumor states there is relatively less phosphorylization of creatine. By using the Cho/Pcr-Cr ratio the concomitant effects of structural and metabolic alteration can thereby be emphasized for diagnostic advantage.

The Cho/Pcr-Cr is a very important and statistically significant marker (p = 0.043) determining the degree of intracranial astrocytoma malignancy.