Figure 4.

fMRI vision mapping, diffusion tensor tractography, and FFMap for a patient with an occipitotemporal tumor. (A) Postcontrast T1-weighted, axial section through the occipital visual cortex showing fMRI activation in response to the expanding ring stimulus. Visually, active voxels (squares) are color coded (inset shows key) to indicate the eccentricity of the stimulus ring that maximally activated each voxel. Voxels representing the center of gaze are colored red or orange, with voxels representing increasingly eccentric portions of the field colored yellow, green, and blue. A tumor mass is evident in the left occipitotemporal region. (B) Diffusion tensor imaging tractography color coded by maximum diffusion direction for each voxel. Optic radiations (white dashed line), which have been displaced dorsally, arch over the tumor region to innervate visually responsive posterior cortex. An embedded 2D axial image shows the location of tumor visible in this single section below the arching optic radiations. Also shown is a lateral fMRI focus (red arrow) activated by a language task. Proximity of the language focus, the optic radiations, and the presumed visual word-form area (not shown) were key landmarks used to guide the subsequent surgical resection of the tumor. (C) Functional Field Map showing the fMRI pattern of visual response (circle symbols) computationally projected onto a diagram of the patient's visual field. Underlay is a visual perimetry chart showing locations of normal visual sensitivity (light gray squares) and impaired sensitivity (dark gray, black squares). It should be noted that visual sensitivity, as measured behaviorally, was impaired throughout much of the right visual field, especially in the upper quadrant. fMRI activation represented by the circle symbols was also sparse in the lateral portion of the right hemifield. However, normal levels of activation (circle symbol density) were observed closer to the vertical meridian, suggesting that the reduced visual sensitivity in the right upper quadrant was not solely due to impairment of the incoming retinal signals. This was consistent with the preserved yet displaced optic radiations evident in the tractography (B). (Color version of figure is available online.)