A new neuroimaging study at the Montreal Neurological Institute and Hospital at McGill University aims to ensure the highest quality of life for patients by assessing their cognitive skills before, during, and after brain tumour surgery. This is done by mapping the important functional brain areas surrounding the tumour in order to decrease the risks during surgery.
Brain tumour surgery requires a delicate balance between removing as much of a tumour as possible in order to ensure a patients' survival and extend life expectancy, while striving to preserve motor, sensory, and cognitive abilities (functional areas of the brain), and thus quality of life. This new study by researchers at the Montreal Neurological Institute and Hospital, published recently in the Journal of Neurosurgery, looks at functional neuroimaging in patients undergoing surgery for the removal of brain tumours. This is done in order to localize important functional areas of the brain so that these can be preserved during the surgical procedure. Functional magnetic resonance imaging (fMRI) has been used extensively to map sensory and motor functions, as well as to define brain regions involved in language processes but, until now, has not been applied to higher-order cognitive functions such as memory. Patients with brain tumours can lead active lives for extended periods following surgery and it is therefore important to consider the preservation of cognitive functions that depend on brain regions close to the tumour in order to maintain the patients' autonomy, and a good postoperative quality of life.
"To the best of our knowledge, this is the first published report applying fMRI to higher cortical processing for the pre-operative evaluation of patients with brain tumours," says Dr. Rolando Del Maestro, Director of the Montreal Neurological Institute's Brain Tumour Research Centre and a lead investigator in the study. Cognitive functions are essential for daily life. For instance, a correct response at a traffic light depends on the selection of possible actions based on previously acquired information and rules. In this situation, for example, green means go and red means stop. Damage to brain areas responsible for this cognitive ability can have a profound affect on the ability of the patient to lead a normal life. Other higher-order cognitive functions include keeping track of information in working memory, or selectively retrieving information from memory - these abilities are associated with the frontal cortex, and are incredibly important for normal functioning in many activities in basic life.
While in the fMRI scanner, pre-operative brain tumour patients are asked to complete a task which assesses the function of the dorsal premotor cortex by requiring them to select between competing actions based on conditional rules. This preoperative fMRI data is then integrated into an image-guided neuronavigation system, which guides neurosurgeons during surgery optimizing the approach for tumour removal in patients and preserving relevant functional regions in the premotor cortical region of the brain.
Patients then undergo post-operative structural MR imaging to show that the resection of the tumour was optimal and that the functional region within the brain's premotor cortex that was involved in the performance of the cognitive task was preserved. Patients in this study showed no deficits in their performance of the task postoperatively, further demonstrating that this specific cognitive function was not altered.
"These preliminary results are promising and suggest that preoperative fMRI is an important tool to assist neurosurgeons in preserving cognitive function in patients who are undergoing brain tumour surgery", stated Dr. Del Maestro. Dr. Del Maestro and his colleagues have also begun intraoperative testing in certain patients, allowing the surgical team to continually monitor and preserve cognitive function at risk during the operation.
This study introduces a new fMRI paradigm to reliably localize and evaluate the cognitive selection of actions in patients with tumours near the dorsal premotor cortex. These techniques are now being applied to assess a broader range of cognitive functions in order to benefit patients with tumours in other brain regions.