gms | German Medical Science

Objective: Space-occupying brain lesions as brain tumors or vessel malformations in the area of the occipital lobe have only been sparsely investigated so far, as this localization is extremely rare with only 1% of cases. It is still unclear how this affects the overall organization of the visual system. To address this issue, we wanted to investigate functional connectivity of functional networks associated with higher visual processing between patients with occipital space-occupying lesion in the occipital cortex and healthy controls.

Methods: 12 patients with brain tumors and 7 patients with vascular lesions in the occipital cortex as well as 19 healthy subjects matched for age and sex were included. During functional MRI patients and subjects were instructed to strictly fixate a blue spot in the center of a grey screen while a flickering checker board spreads from the inner to the outer visual field. Data preprocessing including motion correction of functional data, a registration of functional data on the cortical surface of the anatomical image as well as functional connectivity analysis to assess temporal correlation of brain areas was done using the Statistical Parametric Mapping 12 software and CONN toolbox both based on Matlab. We used 23 Regions of Interest (ROIs) implemented in the CONN toolbox assigned to the Default Mode, Visual, Salience, Dorsal Attention, and Fronto Parietal networks. For each subject, connectivity was calculated using Fischer transformed pairwise correlations. These correlations were first considered separately for each group in one-sample analyses and then compared between the groups.

Results: Compared to their assigned control subjects, the tumor patients and patients with vascular lesion showed reduced intra-network connectivity in the visual and frontoparietal network. Increased connectivity was observed within the salience network in both patient groups compared to controls. In the vascular lesion group there was additional increased connectivity within the default mode network compared to controls.

Conclusion: The results indicate that in the course of the disease, compensatory countermeasures take place in the brain against a brain tumor or a space-occupying brain lesion with the aim of maintaining the performance level and cognitive processes for as long as possible. However, more research is needed in this area to understand the mechanisms and effects of brain tumors and space-consuming brain lesions on surrounding tissue.