Maud Landers1, Stephan Meesters2, Wouter de Baene3, and Geert-Jan Rutten1
1Department of Neurosurgery, Elisabeth TweeSteden Hospital, Tilburg, Netherlands, 2Department of mathematics and Computer Science, University of Technology, Eindhoven, Netherlands, 3Department of Cognitive Neuropsychology, University of Tilburg, Tilburg, Netherlands
Synopsis
Currently there is insufficient knowledge about the right frontal aslant tract’s exact cognitive importance. The aim of this study was to investigate the role of the right frontal aslant tract in executive functions via a lesion-symptom approach. The results suggest that the right frontal aslant tract is involved in shifting attention and phonemic fluency. As a follow-up the main findings were tested and validated in an awake mapping study where stimulation of the right frontal aslant tract lead to deficits in executive functioning.
Methods: We retrospectively examined 72 patients with frontal glial tumors and correlated measures from tractography with cognitive test performances. The measures from tractography were distance between tract and tumor, and structural integrity (fractional anisotropy and mean diffusivity) of the tract.
Results: The results indicated that close proximity of a tumor to the right FAT, as measured with tractography, was related to poorer cognitive performance, in particular on tests of shifting attention and phonemic fluency. A disturbed microstructural integrity of the FAT, as measured by higher mean diffusivity (MD), was also related to impaired performance on these cognitive tests. This involvement was not found for the left tract.
Discussion: The results suggest that the right FAT is involved in executive functions. A better understanding of the functional frontal subcortical anatomy has important implications for neurosurgical practice. In brain tumor surgery, for each patient an optimal balance has to be found between maximal tumor removal (to optimize oncological outcome) and minimal damage to structures that are critical for normal functional performance (to optimize socioprofessional functioning and quality of life)11. Cognitive impairments are often present in glioma patients, and a high incidence is found when measured with neuropsychological tests12, 13. It is likely that patients who have difficulties with shifting attention and phonemic fluency on cognitive tests, as found in our study, also experience problems in daily life. Society is full of distractors, and most of our daily activities (e.g. cooking, planning, driving, working) rely on executive control processes.
Further research: Clinical introduction of new tasks for monitoring cognition during brain tumor surgery should follow a scientific plan. In fact, we believe it is of paramount importance that the neurosurgical team has an a priori hypothesis of the pathways that are tested during surgery. This was the rationale for our lesion-symptom study in 72 patients and provided us with arguments and hypotheses to test the frontal aslant tract in a patient with a right frontal low-grade glioma. In this case, direct electrical stimulation of the frontal aslant tract disrupted working memory and inhibitory functions, and assumptions from our retrospective study were validated. In conclusion, we provided converging evidence that the right frontal aslant tract is involved in executive functions. Further research is needed to assess whether or not damage to the right frontal aslant tract causes permanent deficits in executive functions, and consequently identifies this tract as a critical pathway that should be spared during neurosurgical procedures. Acknowledgements
No acknowledgement found.References
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