gms | German Medical Science

The preservation of eloquent cortex during a neurosurgical intervention is essential for the functional outcome. Functional MRI represents an established concept to map functional units. However, fMRI paradigms are generally active in nature, limiting the method to awake and cooperative patients and to the preoperative period. However, a novel passive fMRI paradigm for localisation analysis of the sensorimotor cortex allows functional analysis of neurologically impaired or anaesthetised patients. The paradigm is based on peripheral electrical nerve stimulation during echo-planar image acquisition. Preceding studies have already established clinical applications of this fMRI-paradigm. The present prospective study evaluates the feasibility of true intraoperative fMRI utilising this paradigm in anaesthetised patients undergoing brain tumor resection. The study focused as well on the technical setup and the intraoperative management.

In 4 anaesthetised patients with centrally localised lesions intraoperative fMRI scans were acquired at 3 distinct stages of the surgical procedure employing an intraoperative 1.5 Tesla MR scanner. The data were analysed statistically and co-registered with the Talairach space. Additionally the data were validated by electrophysiology.

Utilising this passive fMRI paradigm, the sensorimotor cortex could be identified intraoperatively in all patients. We observed a significant change in signal intensity in the course of the operation and detected regularly an inverted BOLD-signal response, which may be caused by an inhibition of cerebrovascular autoregulation under total intravenous anaesthesia (TIVA). Susceptibility artefacts influenced image quality marginally.

We could demonstrate the feasibility of this method to identify the sensorimotor cortex in anaesthetised patients in the surgical setup. Further studies will have to evaluate the BOLD-signal characteristics under anaesthesia and the clinical impact of intraoperative fMRI.