gms | German Medical Science

Objective: Intraoperative MRI (iMRI) plays an increasing role for resection-control of supratentorial gliomas. Because of technical constraints and limitations of patient positioning (e.g. narrow gantry-gap, ante-flexion of the head), iMRI of the posterior fossa remains a challenge. This study evaluates the feasibility and limitations of iMRI-supported surgery of the occipital lobe and the posterior fossa and proposes a new concept of semi-sitting positioning of patients by utilizing an intraoperative 0.15 Tesla MR-scanner.

Methods: In the period from 2004–2008, 187 patients were operated with support of a mobile.15 Tesla MR-scanner. 12 were operated in the prone position via an occipital (n=6), via a parietooccipital (n=3) and via a sub-occipital (n=1) approach.

All relevant parameters concerning intraoperative imaging were collected and analyzed. In addition, early postoperative 1.5 Tesla MRI validated the intraoperatively acquired data. Because of procedural constraints, the prone position is restricted to patients with an average physiognomy. As prone positioning has further specific disadvantages, we conceived a MRI-compatible semi-sitting position, which until now was generally deemed unachievable in combination with iMRI. Preliminary results of this novel procedure are presented as well.

Results: In 11 of the 12 cases ultra-low-field iMRI generated valuable information about the extent of the resection. Image quality was influenced only slightly by skull-base related susceptibility artifacts. For tumor visualization, T1-weighted contrast enhanced sequences (7 minutes acquisition-time, 4mm slice thickness) proved the most favorable.

A total resection was achieved in ten and an intended partial resection in two cases. In one case (oligoastrocytoma III) iMRI prompted further resection. In another case resection control failed due to technical malfunction of the system. On the average, iMRI in prone position extended surgery time by 28 minutes (min: 15, max: 50). The concept of combining the semi-sitting position and iMRI proved to be safe, feasible and advantageous.

Conclusions: Intraoperative MRI of the occipital lobe and the posterior fossa in a prone position is feasible and delivers valuable information despite the fact that it is more complex than supine positioning. Furthermore, our preliminary data suggests that the novel iMRI-compatible semi-sitting position presented here makes it possible to combine the accustomed approach to the posterior fossa with intraoperative MRI.