PMC4922734_01
Functional MRI activity plotted with a threshold of t(150) > 3.91, puncorrected < 0.0001.
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Magnetic resonance (MR) imaging revealed a nonenhancing left frontal mass (Fig. 1, left), and MR spectroscopy characteristics supported a low-to-medium grade tumor. The fMRI confirmed the close relationship of the tumor to Broca's area (within 3-5 mm) with verb generation and object naming tasks (p < 0.05, family-wise error correction) (Fig. 1, right).
(Left) Preoperative axial T2-weighted FLAIR MR image on 1.5 T magnet demonstrating a tumor in the anterior left frontal lobe. (Right) Preoperative fMRI on 3 T magnet indicating proximity of tumor to Broca's area, within 3-5 mm on postprocessed images.
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Chanhassen, MN] (Fig. 2, panels A and B). Once the previous craniotomy flap was reopened and the cortical surface was exposed with good hemostasis, the standard subdural grid was replaced with a high-density 64-contact silicon grid (PMT Corp., Chanhassen, MN), measuring 2.5 x 2.5 cm embedded with platinum iridium electrodes of 2 mm diameter (1 mm exposed) and with an interelectrode distance of 3 mm (Fig. 2, panels C and D).
(A) Intraoperative photograph of left frontal lobe exposure with standard 64-contact subdural grid. (B) Example of subdural grid used during the case, courtesy of PMT Corporation. (C) Intraoperative photograph of high-density grid placed over eloquent cortex previously identified by the standard grid. (D) High-density 64-contact silicon grid used during the case.
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Contacts 1, 2, and 9 were removed for better contour along the cortical surface. Contact 57 was located most anteriorly, contact 64 most superiorly, and contact 8 most posteriorly (Fig. 3). This ECoG paradigm identified electrode contacts 11 and 12 (Fig. 3) as expressive language nodes within a few minutes.
Numbers represent electrode contacts of the standard subdural grid coverage. The tumor margins are displayed as light blue. Electrical stimulation of contacts 11 and 12 (dark blue) caused speech arrest in Broca's area. Electrical stimulation of contacts 23 and 41 (red) caused an electrographic seizure; contacts 1, 2 and 9 (light gray) were removed for better contour along the cortical surface.
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Fig. 4. Functional MRI results were rendered on the surface of the cortex (Fig. 4, left) in similar manner as before, plotting any activation up to 8 mm below the surface. The electrode locations were then projected onto a three-dimensional brain model and custom NeuralAct software (Fig. 4, right) to render activation maps of corresponding ECoG activity.