Functional MRI predicts post-surgical memory following temporal lobectomy

Abstract

Temporal lobectomy is an effective therapy for medically refractory temporal lobe epilepsy (TLE), but may be complicated by amnestic syndromes. Therefore, pre-surgical evaluation to assess the risk/benefit ratio for surgery is required. Intracarotid amobarbital testing (IAT) is currently the most widely used method for assessing pre-surgical memory lateralization, but is relatively invasive. Over the past decade functional MRI (fMRI) has been shown to correlate with IAT for language lateralization, and also for memory lateralization in a small number of patients. This study was carried out to compare fMRI during memory encoding with IAT testing for memory lateralization, and to assess the predictive value of fMRI during memory encoding for post-surgical memory outcome. Thirty-five patients with refractory TLE undergoing pre-surgical evaluation for temporal lobectomy and 30 normal subjects performed a complex visual scene-encoding task during fMRI scanning at 1.5 T using a 10-min protocol. Encoding performance was evaluated with subsequent recognition testing. Twenty-three patients also completed the same task again outside the scanner, an average of 6.9 months following surgery. A region of interest (ROI) analysis was used to quantify activation within hippocampal and a larger mesial temporal lobe ROI consisting of hippocampus, parahippocampus and fusiform gyrus (HPF) as defined by a published template. Normal subjects showed almost symmetrical activation within these ROI. TLE patients showed greater asymmetry. Asymmetry ratios (ARs) from the HPF ROI correlated significantly with memory lateralization by intracarotid amobarbital testing. HPF ARs also correlated significantly with memory outcome, as determined by a change in scene recognition between pre-surgical and post-surgical trials. When absolute activation within the HPF ROI was considered, a significant inverse correlation between activation ipsilateral to temporal lobectomy and memory outcome was observed, with no significant correlation in the contralateral HPF ROI. Although further technical improvements and prospective clinical validation are required, these results suggest that mesial temporal memory activation detected by fMRI during complex visual scene encoding correlates with post-surgical memory outcome and supports the notion that this approach will ultimately contribute to patient management.

Magnetic source imaging versus intracranial electroencephalogram in epilepsy surgery: A prospective study

“…Electrocortical stimulation and the intraarterial amobarbital tests, however, remain the standard of care for brain mapping in epilepsy. Although not an aim of this project, all cases in our population who required primary motor and sensory mapping had confirmation of [25][26][27] Clinical and Technical Validity To discuss validity of results produced by this study, we must address some limitations. The first issue is that of technical validity.…”

The Evolution of Clinical Functional Imaging during the Past 2 Decades and Its Current Impact on Neurosurgical Planning

“…[28][29][30] For example, Janszky et al 28 in their study of 16 patients with right mesial TLE who performed the Roland hometown walking test found a high correlation (r ϭ 0.71) between the preoperative fMRI memory lateralization and individual postoperative memory outcome following right anterior TL resection. Similarly, Richardson et al 30 noted high correlations between preoperative fMRI hippocampal encoding asymmetry and postoperative memory outcome in their study of 10 patients with left TLE who underwent a verbal-encoding task.…”

“…Preoperative fMRI activation asymmetry ratios from the regions of interest correlated significantly with both memory lateralization by preoperative Wada testing and postoperative memory outcome, as determined by a change in scene recognition between presurgical and postsurgical evaluations. 29 …”

Investigations of Brain Network Alterations in Epilepsy Using Functional Magnetic Resonance Imaging

“…Thus, memory paradigms have shown mixed success in lateralizing memory function in TLE compared to the Wada test (Deblaere, et al 2005, Golby, et al 2002, Jokeit, et al 2001. Some fMRI memory paradigms designed to activate the mesial temporal structures have been used with varying levels of success to predict post-surgical memory declines (Frings, et al 2008b, Rabin, et al 2004, Richardson, et al 2006, Wagner, et al 2007). Their general finding was that increased fMRI activation in the mesial temporal lobe ipsilateral to the surgical resection was correlated with increased post-surgical declines, thus supporting the "functional adequacy model" of hippocampal function.…”