Can proton MR spectroscopic and perfusion imaging differentiate between neoplastic and nonneoplastic brain lesions in adults?

Abstract

Background and purpose: Noninvasive diagnosis of brain lesions is important for the correct choice of treatment. Our aims were to investigate whether 1) proton MR spectroscopic imaging ((1)H-MRSI) can aid in differentiating between tumors and nonneoplastic brain lesions, and 2) perfusion MR imaging can improve the classification.

Materials and methods: We retrospectively examined 69 adults with untreated primary brain lesions (brain tumors, n = 36; benign lesions, n = 10; stroke, n = 4; demyelination, n = 10; and stable lesions not confirmed on pathologic examination, n = 9). MR imaging and (1)H-MRSI were performed at 1.5T before biopsy or treatment. Concentrations of N-acetylaspartate (NAA), creatine (Cr), and choline (Cho) in the lesion were expressed as metabolite ratios and were normalized to the contralateral hemisphere. Dynamic susceptibility contrast-enhanced perfusion MR imaging was performed in a subset of patients (n = 32); relative cerebral blood volume (rCBV) was evaluated. Discriminant function analysis was used to identify variables that can predict inclusion in the neoplastic or nonneoplastic lesion groups. Receiver operator characteristic (ROC) analysis was used to compare the discriminatory capability of (1)H-MRSI and perfusion MR imaging.

Results: The discriminant function analysis correctly classified 84.2% of original grouped cases (P < .0001), on the basis of NAA/Cho, Cho(norm), NAA(norm), and NAA/Cr ratios. MRSI and perfusion MR imaging had similar discriminatory capabilities in differentiating tumors from nonneoplastic lesions. With cutoff points of NAA/Cho < or =0.61 and rCBV > or =1.50 (corresponding to diagnosis of the tumors), a sensitivity of 72.2% and specificity of 91.7% in differentiating tumors from nonneoplastic lesions were achieved.

Conclusion: These results suggest a promising role for (1)H-MRSI and perfusion MR imaging in the distinction between brain tumors and nonneoplastic lesions in adults.

Fig 1.

Axial FLAIR image, T2-weighted FSE MR image, axial contrast-enhanced T1-weighted SE MR image, and axial CBV map in a 38-year-old woman with primary CNS lymphoma. There is T2 hyperintensity involving the left temporoparietal lobe. There is minimal mass effect; the lesion exhibits patchy heterogeneous enhancement on the postgadolinium images. The CBV map demonstrates a moderately increased blood volume in the lesion compared with the normal contralateral side (rCBV, 1.66, which is higher than the cutoff point of 1.5). A, B, The abnormal signal intensity of the lesion extended over 8 FLAIR sections (5-mm section thickness, no gap; with 5 sections showing the bulk of the lesion). Images shown of the Cho, Cr, NAA, and lactate metabolites were reconstructed from the MRSI section exhibiting the largest metabolic abnormalities (MRSI, section 2). Axial T1-weighted SE localizer image with proton MR spectra of the lesion (voxel 2) and the corresponding control spectrum (voxel 1) are shown. Compared with the contralateral side, the metabolite images and spectra of the lesion show elevated Cho and Cr, and decreased NAA signals, with an NAA/Cho ratio of 0.58 (below the cutoff point of 0.61). Slight contamination of spectra with lipid signals, most likely because of the patient’s head motion, was noted in this examination.

Fig 2.

Axial FLAIR, T2-weighted FSE, contrast-enhanced T1-weighted SE MR images and axial CBV map in a 27-year-old woman with meningoencephalitis. There is an abnormal high T2 signal intensity in the left frontal lobe with minimal enhancement on the postgadolinium image. The CBV map shows slightly elevated levels of blood volume in the lesion compared with the normal contralateral side, with a rCBV of 1.35. The original diagnosis on the basis of conventional MR imaging favored a neoplasm over an inflammatory cause. At 3 weeks of follow-up (MR spectroscopy was not performed), an overall improved appearance with a decrease in the size of the frontal subcortical and deep white matter T2 signal intensity abnormality was noted. A, B, The abnormal signal intensity of the lesion extended over 5 FSE sections (5-mm section thickness, no gap; with 2 sections showing the bulk of the lesion). One MRSI section (the bottom section shown in the figure) covered the lesion. Images of the Cho, Cr, NAA, and lactate metabolites and proton MR spectra of the lesion (voxel 2) and control region (voxel 1) are shown. The NAA/Cho ratio of 1.15 was above the cutoff point of 0.61, Cho_norm was 0.8, and rCBV was slightly below the cutoff point of 1.5. On the basis of MRSI and perfusion MR imaging, the presence of a nonneoplastic lesion was favored. Discriminant function analysis classified this lesion as nonneoplastic on the basis of MRSI data alone and MRSI and perfusion MR imaging data.

Fig 3.

ROC curves representing discriminatory capability of perfusion MR imaging, ¹H-MRSI and combination of ¹H-MRSI and perfusion MR imaging to differentiate between tumors and nonneoplastic lesions. We constructed the curves using data on 30 subjects evaluated with both perfusion MR imaging and MRSI. The calculated areas under the ROC curves were 0.92 for MRSI, 0.89 for perfusion MR imaging, and 0.96 for the analysis on the basis of MRSI and perfusion MR imaging. We found no significant differences when comparing the areas under the curves, indicating that each procedure had similar discriminatory capability for these subjects.