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M. Necmettin Pamir, Koray Özduman, Erdem Yıldız, Aydın Sav and Alp Dinçer

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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Koray Özduman, Erdem Yıldız, Alp Dinçer, Aydın Sav and M. Necmettin Pamir

Object

The goal of surgery in high-grade gliomas is to maximize the resection of contrast-enhancing tumor without causing additional neurological deficits. Intraoperative MRI improves surgical results. However, when using contrast material intraoperatively, it may be difficult to differentiate between surgically induced enhancement and residual tumor. The purpose of this study was to assess the usefulness of intraoperative dynamic contrast-enhanced T1-weighted MRI to guide this differential diagnosis and test it against tissue histopathology.

Methods

Preoperative and intraoperative dynamic contrast-enhanced MRI was performed in 21 patients with histopathologically confirmed WHO Grade IV gliomas using intraoperative 3-T MRI. Standardized regions of interest (ROIs) were placed manually at 2 separate contrast-enhancing areas at the resection border for each patient. Time-intensity curves (TICs) were generated for each ROI. All ROIs were biopsied and the TIC types were compared with histopathological results. Pharmacokinetic modeling was performed in the last 10 patients to confirm nonparametric TIC analysis findings.

Results

Of the 42 manually selected ROIs in 21 patients, 25 (59.5%) contained solid tumor tissue and 17 (40.5%) retained the brain parenchymal architecture but contained infiltrating tumor cells. Time-intensity curves generated from residual contrast-enhancing tumor and their preoperative counterparts were comparable and showed a quick and persistently increasing slope (“climbing type”). All 17 TICs obtained from regions that did not contain solid tumor tissue were undulating and low in amplitude, compared with those obtained from residual tumors (“low-amplitude type”). Pharmacokinetic findings using the transfer constant, extravascular extracellular volume fraction, rate constant, and initial area under the curve parameters were significantly different for the tumor mass, nontumoral regions, and surgically induced contrast-enhancing areas.

Conclusions

Intraoperative dynamic contrast-enhanced MRI provides quick, reproducible, high-quality, and simply interpreted dynamic MR images in the intraoperative setting and can aid in differentiating surgically induced enhancement from residual tumor.

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Volkan Etus, Ozlem Kurtkaya, Kenan Koc, Ercument Ciftci, Aydin Sav and Savas Ceylan

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Kaya Kiliç, Deniz Konya, Özlem Kurtkaya, Aydin Sav, M. Necmettin Pamir and Türker Kiliç

Object

The authors studied the effect of Gamma Knife irradiation on angiogenesis induced by cerebral arteriovenous malformation (AVM) tissues implanted in the corneas of rats.

Methods

Ten AVM specimens obtained from tissue resections performed at Marmara University between 1998 and 2004 were used. A uniform amount of tissue was implanted into the micropocket between the two epithelial layers of the cornea. Gamma Knife irradiation was applied with dose prescriptions of 15 or 30 Gy to one cornea at 100% iso-dose. Dosing was adjusted so that the implanted cornea of one eye received 1.5 Gy when 15 Gy was applied to the other cornea. Similarly, one cornea received 3 Gy when 30 Gy was applied to the other cornea. Angiogenic activity was graded daily by biomicroscopic observations. Forty-eight other rats were used for microvessel counting and vascularendothelial growth factor (VEGF) staining portions of the experiment. Micropieces of the specimens were again used for corneal implantation. Rats from each group were killed on Days 5, 10, 15, and 20, and four corneas from each group were examined.

Gamma Knife irradiation dose dependently decreased AVM-induced neovascularization in the rat cornea as determined by biomicroscopic grading of angiogenesis, microvessel count, and VEGF expression.

Conclusions

The results suggest that Gamma Knife irradiation inhibits angiogenesis induced by AVM tissue in the cornea angiogenesis model. The data are not directly related to understanding how Gamma Knife irradiation occludes existing AVM vasculature, but to understanding why properly treated AVMs do not recur and do not show neovascularization after Gamma Knife irradiation.

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Cemaliye B. Akyerli, Şirin Yüksel, Özge Can, E. Zeynep Erson-Omay, Yavuz Oktay, Erdal Coşgun, Ege Ülgen, Yiğit Erdemgil, Aydın Sav, Andreas von Deimling, Murat Günel, M. Cengiz Yakıcıer, M. Necmettin Pamir and Koray Özduman

OBJECTIVE

Recent studies have established that hemispheric diffuse gliomas may be grouped into subsets on the basis of molecular markers; these subsets are loosely correlated with the histopathological diagnosis but are strong predictors of clinical tumor behavior. Based on an analysis of molecular and clinical parameters, the authors hypothesized that mutations of the telomerase promoter (TERTp-mut) mark separate oncogenic programs among isocitrate dehydrogenase 1 and/or 2 (IDH) mutant (IDH-mut) and IDH wild-type (IDH-wt) diffuse gliomas independent of histopathology or WHO grade.

METHODS

Four molecular subsets of the combined statuses of IDH and TERT-promoter mutations (double mutant, IDH only, TERT only, and double negative) were defined. Differences in age, anatomical location, molecular genetics, and survival rates in a surgical cohort of 299 patients with a total of 356 hemispheric diffuse gliomas (WHO Grade II, III, or IV) were analyzed.

RESULTS

TERTp-mut were present in 38.8% of IDH-mut and 70.2% of IDH-wt gliomas. The mutational status was stable in each patient at 57 recurrence events over a 2645-month cumulative follow-up period. Among patients with IDH-mut gliomas, those in the double-mutant subset had better survival and a lower incidence of malignant degeneration than those in the IDH-only subset. Of patients in the double-mutant subset, 96.3% were also positive for 1p/19q codeletions. All patients with 1p/19q codeletions had TERTp-mut. In patients with IDH-mut glioma, epidermal growth factor receptor or phosphatase and tensin homolog mutations were not observed, and copy-number variations were uncommon. Among IDH-wt gliomas, the TERT-only subset was associated with significantly higher age, higher Ki-67 labeling index, primary glioblastoma-specific oncogenic changes, and poor survival. The double-negative subset was genetically and biologically heterogeneous. Survival analyses (Kaplan-Meier, multivariate, and regression-tree analyses) confirmed that patients in the 4 molecular subsets had distinct prognoses.

CONCLUSIONS

Molecular subsets result in different tumor biology and clinical behaviors in hemispheric diffuse gliomas.