Background: The presence of residual tumor is crucial in decision-making for low-grade gliomas (LGGs), because patients older than 40 years of age with residual tumor are considered for adjuvant treatment. There are hints that early postoperative fluid-attenuated inversion recovery (FLAIR) and T2 (within 48 hours) may overestimate residual tumor volume in LGG. Intraoperative magnetic resonance imaging (MRI) without subsequent resection or ultra-early postoperative MRI may assess the amount of residual tumor more adequately. To evaluate the utility of postoperative imaging in LGG, we volumetrically analyzed intraoperative, early, and late (3-4 months after surgery) postoperative MRIs of LGGs.
Patients and methods: A total of 33 patients with LGG were assessed retrospectively. Residual tumor was defined as signal-enhanced tissue in T2 and FLAIR. Volumetric assessment was performed with intraoperative, early, and late postoperative T2/FLAIR via Brainlab-iPlan 3.0. Wilcoxon and χ(2) tests were used for statistical analysis.
Results: A significant difference of FLAIR/T2 abnormalities was found in intraoperative and early postoperative MRIs (FLAIR mean volume = 5.433 cm(3), T2 mean volume = 3.374 cm(3) vs. FLAIR mean volume = 14.090 cm(3), P = 0.002, T2 mean volume = 7.597 cm(3), P = 0.006). There was no significant difference between intraoperative and late postoperative FLAIR/T2 abnormalities (late postoperative FLAIR/T2 mean volume = 5.560 cm(3) and 2.370 cm(3), P = 0.520, P = 0.398), whereas a significant difference was detected between early and late postoperative images (FLAIR, P < 0.0001; T2, P < 0.00001).
Conclusion: Intraoperative MRI without further resection or ultra-early postoperative MRI seems to reflect the actual volume of residual tumor in LGG more precisely compared with early postoperative MRI and therefore seems to be more useful regarding decisions for adjuvant therapy.
Keywords: FLAIR; Intraoperative MRI; Low-grade glioma; T2.
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