gms | German Medical Science

Objective: Functional brain mapping during surgery in awake patients minimizes the consequences of tumour removal on behaviour. Beyond the identification of the so-called “motor strip”, mapping should also identify association areas, that represent the largest part of the cerebral cortex. Lesions in these regions and in their subcortical systems do not determine obvious neurological defects, but complex disorders that severely affect daily life.

Methods: We have implemented a number of neuropsychological tests to asses the patients’ cognitive functions, preoperatively, during surgery, and postoperatively. Testing is tailored to brain region which is target of surgery, based on knowledge of its role on behaviour, as it emerges from neuroanatomical and neurophysiolocal studies in non-human primates, as well as from neuropsychological studies. Testing cognitive function during surgery in awake patients requires the presentation of a battery of tests and the assessment of patients’ behaviour after inactivation of the brain tissue that is around or even inside a tumour lesion.

Results: We have used this approach on two subjects suffering from high-grade gliomas, the first localized in the right Superior Parietal Lobule (BA 5/7), the second in the posterior part of the left Superior Frontal Gyrus (BA 6). Both patients were tested for Optic Ataxia (OA) and Hemispatial Neglect, and in several visuomotor tasks requiring coordinated eye-hand movement. Preoperatively, in the parietal patient we only found a severe OA when he reached to peripheral visual target with the left hand. During surgery, the inactivation of a region located posterior to the tumoral mass resulted in misreaching also with the right hand, and this was a clear indication for sparing this region. After surgery, a mild OA persisted with the left arm. In the frontal patient no obvious impairment was found under all testing condition. The main defect observed consisted in arrest of language production in a reading task, after inactivation of a medial fibres bundle underlying the Supplementary Motor Area.

Conclusions: The consequences of surgery on patients’ behaviour will strongly depend on the depth of neuropsychological assessment at all stages of treatment. The relatively “slow” growth of tumours, as compared to stroke, might favour reorganization of cortical function, due to brain plasticity, and makes preoperative cognitive disorders often elusive and difficult to detect on qualitative grounds.