Preoperative correlation of anatomical and functional imaging and combined use of a neuronavigation system and intraoperative direct cortical and subcortical stimulation techniques for preserving motor function

Improvement of the prognosis for patients with gliomas near the motor strip requires maximum tumor resection with preservation of the motor function. Preoperative functional and anatomical imaging was used to correlate the anatomical relationship between the tumor, the motor strip, and the descending motor pathways. A magnetic resonance (MR) imaging-linked whole head magnetoencephalography system was used to localize the somatosensory evoked magnetic fields caused by stimuli of the lip, the thumb, the median nerve, and the ulnar nerve. Functional MR imaging was performed with a 1.5 Tesla scanner during repetitive opening and closing of each hand and lip protrusion. The hand-digit motor cortices were located in the so-called "precentral knob" inside the characteristic inverted-omega shape on axial MR images of the brain on the basis of the pattern of the sulcus. The hand-digit somatosensory cortices were localized at the lateral shoulder of the inverted-omega shape. The operative field was simulated by superimposing the superficial venous image obtained by MR imaging using a three-dimensional phase contrast technique on the surface anatomy scan (SAS) of the brain obtained by the multiple-slice SAS method. The hand-digit motor cortices were located in the so-called "middle knee" or "Broca's middle bend". The SAS superimposed on the superficial venous image revealed the surface anatomical relationship between the tumor and the hand-digit motor cortices. Fiber mapping images using diffusion-weighted MR imaging are useful for evaluating the white matter neuronal tracts including the descending motor pathways. Combination of these preoperative anatomical and functional imaging methods allowed projection of the best surgical approach and extent of resection of tumors around the motor strip without causing additional motor deficit. Maximum tumor resection with minimal morbidity is possible using intraoperative neurophysiological mapping methods such as direct cortical and subcortical simulation techniques to localize the motor pathways with a neuronavigation system.