Diagnostic Accuracy of Neuroimaging to Delineate Diffuse Gliomas within the Brain: A Meta-Analysis

BACKGROUND:Brain imaging in diffuse glioma is used for diagnosis, treatment planning, and follow-up.PURPOSE:In this meta-analysis, we address the diagnostic accuracy of imaging to delineate diffuse glioma.DATA SOURCES:We systematically searched studies of adults with diffuse gliomas and correlation of imaging with histopathology.STUDY SELECTION:Study inclusion was based on quality criteria. Individual patient data were used, if available.DATA ANALYSIS:A hierarchic summary receiver operating characteristic method was applied. Low- and high-grade gliomas were analyzed in subgroups.DATA SYNTHESIS:Sixty-one studies described 3532 samples in 1309 patients. The mean Standard for Reporting of Diagnostic Accuracy score (13/25) indicated suboptimal reporting quality. For diffuse gliomas as a whole, the diagnostic accuracy was best with T2-weighted imaging, measured as area under the curve, false-positive rate, true-positive rate, and diagnostic odds ratio of 95.6%, 3.3%, 82%, and 152. For low-grade gliomas, the diagnostic accuracy of T2-weighted imaging as a reference was 89.0%, 0.4%, 44.7%, and 205; and for high-grade gliomas, with T1-weighted gadolinium-enhanced MR imaging as a reference, it was 80.7%, 16.8%, 73.3%, and 14.8. In high-grade gliomas, MR spectroscopy (85.7%, 35.0%, 85.7%, and 12.4) and ¹¹C methionine–PET (85.1%, 38.7%, 93.7%, and 26.6) performed better than the reference imaging.LIMITATIONS:True-negative samples were underrepresented in these data, so false-positive rates are probably less reliable than true-positive rates. Multimodality imaging data were unavailable.CONCLUSIONS:The diagnostic accuracy of commonly used imaging is better for delineation of low-grade gliomas than high-grade gliomas on the basis of limited evidence. Improvement is indicated from advanced techniques, such as MR spectroscopy and PET.

Diffuse gliomas are the most common primary brain tumors in adults, with an annual incidence of approximately 6 per 100,000. Despite advances in neurosurgery, radiation therapy, and chemotherapy, gliomas are fatal.¹ Brain imaging is indispensable for diagnosis, treatment planning, evaluation, and follow-up. Although imaging standards to plan resection and radiation therapy vary between institutions and specialists, conventional imaging is in common use, typically consisting of T1-weighted MR imaging before and after gadolinium and T2/FLAIR-weighted imaging for gliomas. Of these conventional sequences, T2/FLAIR-weighted imaging is often considered as a reference for low-grade gliomas, and T1-weighted gadolinium-enhanced imaging, for high-grade gliomas in neurosurgical planning, combined with T2-weighted imaging in radiation therapy planning.^2,3Compared with other cancer types, accurate delineation of gliomas within the brain for treatment planning is particularly important due to the proximity of eloquent brain structures, which are vulnerable to surgery and radiation therapy.⁴ Conversely, more extensive resections and boosted radiation therapy correlate with longer survival.^5–7 At the same time, clinical observations challenge the diagnostic accuracy of current imaging protocols: Gliomas recur even after a radiologically complete resection,^8,9 and glioma cells have been detected outside MR imaging abnormalities.^10,11 Brain imaging techniques, such as multivoxel spectroscopy and PET, were developed to improve tumor grading and delineation.^12,13Inherent in any regional treatment, such as surgery and radiation therapy, is the need to delineate a target volume, which mandates a dichotomous classification into tumor and normal tissue. Low- and high-grade gliomas have different treatment strategies and prognosis, while both are characterized by diffuse tumor infiltration. This supports our pooled analysis for diffuse glioma in addition to subgroup analysis by glioma grade. More accurate glioma delineation may improve the consistency between treatment results and survival. For instance, more accurate delineation may serve to identify patients eligible for more aggressive surgery than would have been considered on the basis of conventional imaging and may identify patients with glioma infiltration beyond meaningful surgical therapy so that useless and possibly harmful resections can be avoided.The diagnostic accuracy of imaging techniques to delineate gliomas has not been systematically addressed, to our knowledge. In this meta-analysis, we estimate and compare the diagnostic accuracies of conventional imaging techniques and advanced MR imaging and PET to delineate newly diagnosed diffuse gliomas within brain tissue in adults.