gms | German Medical Science

Objective: The areas surrounding the calcarine sulcus of the occipital cortex exhibit a retinotopic organization by representing a spatial map of the retinal surface. Therefore, lesions in the occipital cortex may lead to visual field deficits. To avoid those in patients with space-occupying lesions of the occipital cortex we applied retinotopic mapping in presurgical functional imaging. We looked for feasibility of retinotopic mapping in presence of a lesion. Additionally, we compared brain activation of patients with occipital lesions with healthy subjects.

Methods: 15 patients with lesions on the occipital cortex (8 brain tumors, 2 metastatic lesions, 5 vascular malformations) and 15 healthy subjects matched for age and sex were included. To asses retinotopic organization of the visual field a visual eccentricity paradigm was applied during functional MRI. Patients were instructed to strictly fixate a blue spot in the center of a gray screen while a flickering checker board spreads from the inner to the outer visual field. To achieve an exact cortical retinotopy representation data analysis was done using Freesurfer version 6.0 including motion correction, skull stripping, normalization, white matter segmentation and smoothing. Statistical analysis on single a group level as well as group differences were conducted on the basis of the general linear model. To address lesion size effects the patient group was stratified using a median split according to lesion size.

Results: Retinotopic organization of visual eccentricity in presence of a space occupying lesion in the occipital cortex could be reconstructed in all patients of this study sample independently of lesion entity. The retinotopic organization of the inner, middle and outer visual field could be shown in patients and healthy subjects. However, patients showed lower activation in primary visual areas belonging to those retinotopic association areas compared to healthy controls. Additionally, patients with smaller lesions exhibited more activation associated with stimulation of the visual field in the precuneus and the inferior parietal and temporal cortex.

Conclusion: These results show the feasibility of retinotopy mapping in patients with occipital lesions. But, those patients showed similar reduced activation of the visual cortex due to retinotopic stimulation which negatively correlates with lesion size.