gms | German Medical Science

Objective: In surgical treatment of low-grade gliomas differentiation between pathological and normal tissue is challenging. Intraoperative MRI (ioMRI) and conventional low frequency intraoperative ultrasound (lfioUS) are the most commonly used intraoperative imaging modalities. The impact of high-frequency intraoperative ultrasound (hfioUS), even though highly beneficial e.g. in peripheral nerve surgery, is unknown for intracranial use. Aim of the study is to evaluate ideal application and typical interactions of ioMRI, lfioUS and the new hfioUS in order to optimize surgical workflow.

Method: Prospectively, we included twelve patients suffering from a non contrast-enhancing axial lesion. Typical procedural workflow in the ioMRI suite was recorded. Main focus was duration, frequency, timing and rational of application of lfioUS, hfioUS and ioMRI. In addition, a standardized questionnaire using Likert scales (1=excellent, 6=poor), was applied to assess surgeons subjective rating concerning image quality, benefit from usage, estimated brainshift and residual tumor mass.

Results: HfioUS was used more often (63%) than lfioUS (37%) and was rated to be helpful in 79% vs. 67% of applications. Single scan time of lfioUS and hfioUS showed no difference. Preparation time for registration in neuronavigation was shorter in lfioUS. Image quality for tumor detection was rated with 1.8 in hfioUS and with 3.3 in lfioUS. Mayor aim of hfioUS application was resection control. Surgeons rated hfioUS to be helpful in this regard in 89% vs. 43% for lfioUS. Most common goal of application of lfioUS was orientation which was rated to beneficial in 100% vs. 25% in hfioUS. For tissue differentiation and brainshift control only hfioUS was rated to be helpful. Using hfioUS surgeons estimated residual tumor volume before ioMRI, with a deviation of 5% only. Mean ioMRI duration including preparation and post processing was 54 minutes. In 80% of surgeries, a single ioMRI was conducted. Altogether further resection was performed in 60%. Average residual volume was 3.9cc.

Conclusions: The new hfioUS has proved to be helpful as an adjunct to ioMRI. Ideal application was tumor detection during and after resection. Except for orientation, hfioUS was rated to be more beneficial than lfioUS for all other aspects. Especially brainshift and residual tumor were assessed mainly with hfioUS. The application of hfioUS as a quickly applicable, high quality imaging tool, increased tumor control and prevented multiple MRI scans.