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, 49 (8), 1377-94

Use of Preoperative Functional MRI to Predict Verbal Memory Decline After Temporal Lobe Epilepsy Surgery

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Use of Preoperative Functional MRI to Predict Verbal Memory Decline After Temporal Lobe Epilepsy Surgery

Jeffrey R Binder et al. Epilepsia.

Abstract

Purpose: Verbal memory decline is a frequent complication of left anterior temporal lobectomy (L-ATL). The goal of this study was to determine whether preoperative language mapping using functional magnetic resonance imaging (fMRI) is useful for predicting which patients are likely to experience verbal memory decline after L-ATL.

Methods: Sixty L-ATL patients underwent preoperative language mapping with fMRI, preoperative intracarotid amobarbital (Wada) testing for language and memory lateralization, and pre- and postoperative neuropsychological testing. Demographic, historical, neuropsychological, and imaging variables were examined for their ability to predict pre- to postoperative memory change.

Results: Verbal memory decline occurred in over 30% of patients. Good preoperative performance, late age at onset of epilepsy, left dominance on fMRI, and left dominance on the Wada test were each predictive of memory decline. Preoperative performance and age at onset together accounted for roughly 50% of the variance in memory outcome (p < 0.001), and fMRI explained an additional 10% of this variance (p <or= 0.003). Neither Wada memory asymmetry nor Wada language asymmetry added additional predictive power beyond these noninvasive measures.

Discussion: Preoperative fMRI is useful for identifying patients at high risk for verbal memory decline prior to L-ATL surgery. Lateralization of language is correlated with lateralization of verbal memory, whereas Wada memory testing is either insufficiently reliable or insufficiently material-specific to accurately localize verbal memory processes.

Figures

Figure 1
Figure 1
Relationships between fMRI lateralization indexes and individual memory change scores (CLTR, LTS, Delayed Recall) in the L-ATL patients.
Figure 2
Figure 2
Relationships between Wada memory asymmetries and individual memory change scores (CLTR, LTS, Delayed Recall) in the L-ATL patients.
Figure 3
Figure 3
Predicted vs. observed individual memory change scores (CLTR, LTS, Delayed Recall) in the L-ATL patients.
Figure 4
Figure 4
Example fMRI activation maps are shown in serial sagittal sections through the left (L) and right (R) hemispheres at 10-mm intervals through standard stereotaxic space. All maps are thresholded at map-wise corrected p < 0.05 using a voxel-wise p < 0.001 and minimal cluster size of 300 μl. The top panel shows the average activation pattern for this task contrast obtained from 30 healthy adults (see (Binder et al., 1997) for details). The remaining panels show selected individuals described in Table 5, indicated by case number.
Figure 5
Figure 5
FMRI activation maps for four additional patients described in Table 5.
Figure 6
Figure 6
Schematic diagram of a hypothetical model of memory and language representation in temporal lobe epilepsy (TLE). The yellow ovals represent language systems, red rectangles represent verbal episodic memory encoding systems in the medial temporal lobe (MTL), and blue rectangles represent non-verbal episodic memory encoding systems in the MTL. (A) Typical state in healthy subjects and patients with late-onset epilepsy. Language and verbal memory processes are strongly left-lateralized, placing the patient at high risk for verbal memory decline. (B) Chronic left TLE without shift. The left MTL is dysfunctional, causing Wada memory lateralization to the right, but verbal memory has not shifted, leaving the patient at high risk for verbal memory decline. (C) Chronic left TLE with shift. Both language and verbal memory functions have shifted partially to the right, lowering the risk for verbal memory decline. Note the relative lack of correspondence, across patient types, between Wada memory asymmetry and level of risk.

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