Functional magnetic resonance imaging of the visual cortex performed in children under sedation to assist in presurgical planning

Clinical article

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Object

Advances in brain imaging have allowed for more sophisticated mapping of crucial neural structures. Functional MRI (fMRI) measures local changes in blood oxygenation associated with changes in neural activity and is useful in mapping cortical activation. Applications of this imaging modality have generally been restricted to cooperative patients; however, fMRI has proven successful in localizing the motor cortex for neurosurgical planning in uncooperative children under sedation. The authors demonstrate that the use of fMRI to localize the visual cortex in sedated children can be safely and effectively performed, allowing for more accurate presurgical planning to spare visual structures.

Methods

Between 2007 and 2009, 11 children (age range 1–11 years) underwent fMRI for neurosurgical planning while under sedation. Blood oxygen level–dependent fMRI was performed to detect visual cortex activation during stimulation through closed eyelids. Visual stimulation was presented in block design with periods of flashing light alternated with darkness.

Results

Functional MRI was successful in identifying visual cortex in each of the 11 children tested. There were no complications with propofol sedation or the fMRI. All children suffered from epilepsy, 5 had brain tumors, and 1 had tuberous sclerosis. After fMRI was performed, 6 patients underwent surgery. Frameless stereotactic guidance was synchronized with fMRI data to design an approach to spare visual structures during resection. There were no cases where a false negative led to unexpected visual field deficits or other side effects of surgery. In 2 cases, the fMRI results demonstrated that the tracts were already disrupted: in one case from a prior tumor operation and in another from dysplasia.

Conclusions

Functional MRI for evaluation of visual pathways can be safely and reproducibly performed in young or uncooperative children under light sedation. Identification of primary visual cortex aids in presurgical planning to avoid vision loss in appropriately selected patients.

Abbreviations used in this paper:BOLD = blood oxygen level–dependent; DTI = diffusion tensor imaging; fMRI = functional MRI.

Article Information

Address correspondence to: Frederick A. Boop, M.D., Semmes-Murphey Clinic, 6325 Humphreys Boulevard, Memphis, Tennessee 38120. email: faboop@aol.com.

Please include this information when citing this paper: published online March 8, 2013; DOI: 10.3171/2013.1.PEDS12401.

© AANS, except where prohibited by US copyright law.

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Figures

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    Case 1. Localization of the primary visual cortex in a 3-year-old boy with tuberous sclerosis and seizures. Functional MR images obtained in the sedated patient in sagittal (A), coronal (B), and axial (C) planes demonstrating multiple tubers (red arrows) around the visual cortex (red areas). Two separate transcortical approaches were performed to leave the visual cortex and pathways intact. The red areas indicate the areas of primary visual cortex activation that were identified with a negative BOLD signal change during visual stimulation.

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    Case 2. Images obtained in an 8-year-old boy with seizures and a right temporooccipital low-grade glioma demonstrating the localization (the image is reversed in our fMRI software). The crosshairs in all 3 planes—sagittal (A), coronal (B), and axial (C)—are centered on the tumor in the right parahippocampal gyrus. The overlays demonstrate primary visual cortex activation (blue areas indicate negative BOLD signal and red areas indicate positive BOLD signal). The patient underwent gross-total resection (D) and has normal visual fields postoperatively. Tractography (E) was performed utilizing the information gained by fMRI of his visual cortex and demonstrated that his tumor had displaced the geniculocalcarine tracts laterally, making an occipital interhemispheric approach the best choice for preservation of the patient's geniculocalcarine tract and occipital cortex.

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