Functional brain mapping defines visual cortex plasticity and guides microsurgical resection in occipital arteriovenous malformations. A prospective study.
Functional Brain Mapping Defines Visual Cortex Plasticity and Guides Microsurgical Resection in Occipital Arteriovenous Malformations. a Prospective Study
Resident University of Toronto Toronto, Ontario, Canada
Introduction: Occipital arteriovenous malformations (AVMs) are challenging lesions for neurosurgical management due to their close proximity to the visual cortex and the optic tract pathways. Given that these are developmental lesions we hypothesize that there is plasticity in the brain architecture and physiology enabling preservation of normal conscious vision in patient with visual cortex AVMs.
Methods: Five patients with unruptured AVM on the occipital cortex were prospectively recruited in this study. Formal visual field testing and visual evoked potential recordings were performed. Neuronavigated transmagnetic stimulation (nTMS) was used to induce phosphenes and map the visual cortex in the affected and non affected hemispheres. nTMS-based DTI was used to reconstruct the axonal pathways of the visual system in both hemispheres. After this battery of investigations, all patients were discussed in our multidisciplinary AVM conference and underwent microsurgical resection.
Results: Visual field testing in all patients revealed normal conscious vision. Moreover, visual evoked potential recordings demonstrated no difference between the affected and unaffected hemisphere in all patients. However, retinotopic mapping using neuronavigated-transcranial magnetic stimulation did not reveal phosphene perception in the early and dorsal visual cortex of the affected hemisphere compared to control. Ectopic phosphenes were mapped in a small area lateral and caudal to the lesions in all patients; indicating ectopic displacement of the visual cortex. nTMS based DTI showed that the visual pathway tracts were wrapped around the AVM in all cases. All patients retained normal vision after surgical resection of AVM. Post-operative DSA used to confirm complete obliteration.
Conclusion : Our findings demonstrate that visual cortex is displaced in patients with unruptured occipital AVMs. Our battery of test was able to map these plastic changes in the brain architecture and physiology. This pre-operative functional mapping served as an important adjunct in decision making and enabled complete AVM resection, with no post-operative visual field deficits.
