Noninvasive evaluation of the malignant potential of intracranial meningiomas performed using proton magnetic resonance spectroscopy.

OBJECT

Controversy exists about correlations between histological tumor grade and magnetic resonance (MR) spectroscopy data. The authors studied single-voxel proton MR spectroscopy as a noninvasive way to evaluate grade of malignancy in intracranial meningiomas.

METHODS

The authors compared the results of MR spectroscopy with those derived by the MIB-1 staining index (SI) in 29 meningiomas. Proton MR spectroscopy was performed using stimulated echo acquisition and volume-localized solvent-attenuated proton nuclear MR sequences before surgery or other therapy. Twenty-four tumors were histologically benign (13 meningothelial, three fibrous, four transitional, three angiomatous, and one chordoid); four were atypical (Grade II), and one was papillary (Grade III). The mean MIB-1 SI in the benign group was significantly lower than those in the other groups (p = 0.0041). The mean choline-containing compound (Cho)/ creatine and phosphocreatine (Cr) ratios in the benign and nonbenign groups were 2.56+/-1.26 and 7.85+/-3.23, respectively (p = 0.0002). A significant linear correlation was observed between the Cho/Cr ratio and the MIB-1 SI (r0.05 = 0.74, p<0.001). Necrosis was present histologically in four of the five meningiomas classified either as atypical or papillary. Magnetic resonance spectroscopy revealed a methylene signal in these meningiomas that was not detected in benign meningiomas. Of the five meningiomas in which only a lactate signal was observed, two were benign and the MIB-1 SI in these two benign meningiomas was higher than the mean value for the benign group. Alanine, detected in 12 of 30 meningiomas, did not correlate with either tumor grade or Cho/Cr ratio.

CONCLUSIONS

Proton MR spectroscopy is a useful diagnostic method for determining the proliferative or malignant potential of meningiomas according to the Cho/Cr ratio. A lactate and/or methylene signal suggests a high-grade tumor.