Intraoperative High-field MRI Combined With Fiber Tract Neuronavigation Guided Resection Of Cerebral Lesions Involving Optic Radiation

Background:intraoperative magnetic resonance imaging (iMRI) combined with optic radiation neuronavigation may be safer for resection of cerebral lesions involving the optic radiationObjective:to investigate whether iMRI combined with optic radiation neuronavigation can help to maximize tumor resection while protecting the patient's visual field.Methods:44 patients with cerebral tumors adjacent to the optic radiation were enrolled in the; study. Both conventional MRI and DTI were performed on a 1.5T scanner (Siemens Espree, Erlangen, Germany) using the same protocol. We used the "Fiber Tracking" module of the neuronavigation planning software iPlan 2.6 (BrainLab, Feldkirchen, Germany) to reconstruct the optic radiation.The reconstructed optic radiations were observed to design a reasonable surgical plan. During the surgery, microscope-based fiber tract neuronavigation was routinely implemented.Intra-operative scans were performed immediately when the operator believed that the:lesion has been totally removed or when intra-operative scanning was necessary for "brain shift" correction. The patients underwent visual field examination both preoperatively and postoperatively. Visual field analysis was performed with a. Humphrey Field AnalyserⅡ(Carl Zeiss, Meditec, Japan) by an experienced ophthalmologist who was blinded to the results of the neuroimaging findings. All of the postoperative visual field examinations were carried out at 3 months after the surgery. The pathological diagnosis, the distance between the lesion and optic radiation, the lesion location (lateral or not to the optic radiation) and the course of the optic radiation (stretched or not) were categorized and their relationship to the visual field defect were discussed.Results:Analysis of the visible relationship between the optic radiation and the lesion led to a change in the surgical approach in six patients (14%). There was a discrepancy between the surgeon's estimation regarding the extent of the resection prior to iMRI scanning, and the actual results of surgery assessed after the first iMRI. Of the total discrepant patients, Gap≥10% in nine cases. The mean tumor residual rate for glioma patients was 5.3%(n=36) and 0% for non-glioma lesions (n=8). iMRI and fiber tract neuronavigation increased the average size of resection (first and last iMRI scanning; 88.3% versus 95.7%, P<0.01). Visual fields after surgery improved in five cases (11.4%), exhibited no change in 36 cases (81.8%), and aggravated in three cases (6.8%). Spearman rank correlation analysis showed that the deterioration of visual field were also related to tract stretching (rs=0.446, P<0.01) and that lateral localization (rs=0.415, P<0.01).Conclusion:Preoperative surgical planning based on DTI findings facilitated optimization of the surgical approach. For improved protection of the optic radiation, an iMRI scan should be performed and the neuronavigation updated in a timely manner. Additionally, the manipulation should be carried out lightly and softly. Intraoperative MRI combined with neuronavigation can help improve tumor removal while preserving the integrity of the optic radiation in most cases.