Intraoperative magnetic resonance spectroscopy for identification of residual tumor during low-grade glioma surgery

Abstract

M axiMal safe resection is currently the most effective form of therapy for hemispheric LGGs and patients benefit from the extent of resection. 1,7,16,20 Intraoperative MRI has been used with success in LGG surgery, and the technique has been shown to both increase the extent of resection 2,[10][11][12]21,22,25 and significantly decrease recurrence and death rate in patients with LGGs. 2During LGG surgery, ioMRI can detect residual tumor tissue that cannot be identified by visual inspection or intraoperative ultrasonography. 8,15,25 The tumor mass is defined as the T2-hyperintense area and the extent of resection is based on comparison of intraoperatively acquired T2-weighted images with preoperative ones. However, especially after resection of large LGGs with mass effect, intraoperative images may show T2-hyperintense areas at the resection border, and a differential diagnosis between tumoral and nontumoral tissue may be difficult.15 The difficulty lies in that both tumor and nontumoral changes such as infarction, edema, or iatrogenic contusion or other surgically induced changes can appear similarly as T2 hyperintensities on MRI. This is a potential limiting factor for an optimum resection in certain Object. The authors had previously shown that 3-T intraoperative MRI (ioMRI) detects residual tumor tissue during low-grade glioma and that it helps to increase the extent of resection. In a proportion of their cases, however, the ioMRI disclosed T2-hyperintense areas at the tumor resection border after the initial resection attempt and prompted a differential diagnosis between residual tumor and nontumoral changes. To guide this differential diagnosis the authors used intraoperative long-TE single-voxel proton MR spectroscopy (ioMRS) and tested the correlation of these findings with findings from pathological examination of resected tissue.Methods. Patients who were undergoing surgery for hemispheric or insular WHO Grade II gliomas and were found to have T2 changes around the resection cavity at the initial ioMRI were prospectively examined with ioMRS and biopsies were taken from corresponding localizations. In 14 consecutive patients, the ioMRS diagnosis in 20 voxels of interest was tested against the histopathological diagnosis. Intraoperative diffusion-weighted imaging (ioDWI) was also performed, as a part of the routine imaging, to rule out surgically induced changes, which could also appear as T2 hyperintensity.Results. Presence of tumor was documented in 14 (70%) of the 20 T2-hyperintense areas by histopathological examination. The sensitivity of ioMRS for identifying residual tumor was 85.7%, the specificity was 100%, the positive predictive value was 100%, and the negative predictive value was 75%. The specificity of ioDWI for surgically induced changes was high (100%), but the sensitivity was only 60%.Conclusions. This is the first clinical series to indicate that ioMRS can be used to differentiate residual tumor from nontumoral changes around the resection cavity, with high sensitivity and specificity. ...

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