Proton MR spectroscopy and preoperative diagnostic accuracy: an evaluation of intracranial mass lesions characterized by stereotactic biopsy findings

Abstract

Background and purpose: MR imaging has made it easier to distinguish among the different types of intracranial mass lesions. Nevertheless, it is sometimes impossible to base a diagnosis solely on clinical and neuroradiologic findings, and, in these cases, biopsy must be performed. The purpose of this study was to evaluate the hypothesis that proton MR spectroscopy is able to improve preoperative diagnostic accuracy in cases of intracranial tumors and may therefore obviate stereotactic biopsy.

Methods: Twenty-six patients with intracranial tumors underwent MR imaging, proton MR spectroscopy, and stereotactic biopsy. MR spectroscopic findings were evaluated for the distribution pattern of pathologic spectra (NAA/Cho ratio < 1) across the lesion and neighboring tissue, for signal ratios in different tumor types, and for their potential to improve preoperative diagnostic accuracy.

Results: Gliomas and lymphomas showed pathologic spectra outside the area of contrast enhancement while four nonastrocytic circumscribed tumors (meningioma, pineocytoma, metastasis, and germinoma) showed no pathologic spectra outside the region of enhancement. No significant correlation was found between different tumor types and signal ratios. MR spectroscopy improved diagnostic accuracy by differentiating infiltrative from circumscribed tumors; however, diagnostic accuracy was not improved in terms of differentiating the types of infiltrative or circumscribed lesions.

Conclusion: MR spectroscopy can improve diagnostic accuracy by differentiating circumscribed brain lesions from histologically infiltrating processes, which may be difficult or impossible solely on the basis of clinical or neuroradiologic findings.

fig 1.

A–G, Patient with a pineocytoma: six MR spectra (A–F) represent voxels outlined on the axial, contrast-enhanced T1-weighted MR image (G). Only voxels covering contrast-enhancing parts of the lesion showed pathologic MR spectra.

fig 2.

←A–Q, Patient with a cystic high-grade glioma: the images show the heterogeneity of spectra across the lesion. A is an axial, contrast-enhanced T1-weighted MR image with the measurement area and voxels represented by the MR spectra in B–Q outlined; B–I represent voxels in the vertical row (top to bottom) and (J–Q) represent voxels in the horizontal row (left to right). The spectrum representing the intersection of the vertical and horizontal rows is shown twice (H and P)

fig 2.

fig 3.

Scattergram of signal ratios in stereotactic biopsy target points for different tumor types. LA = low-grade astrocytoma (n = 4), HA = high-grade astrocytoma (n = 11), LY = lymphoma (n = 3)

fig 4.

MR spectroscopic scout images and corresponding spectra represent the stereotactic biopsy target points in a high-grade (A and B) and a low-grade (C and D) astrocytoma. The two spectra are almost identical, and signal ratios could not be used to grade the tumors