Structural Changes in the Contralateral following Laser Interstitial Therapy for Selective Amygdalohippocampectomy Allen Ho MD; Michael Zeineh MD, PhD; Eric S Sussman MD; Robert M. Lober MD PhD; Gerald A. Grant MD; Max Wintermark MD; Casey H. Halpern MD Department of and Department of Radiology, Stanford School of Medicine

Introduction ROIs for these structures were selected as Learning Objectives depicted in Figures 1 and 2 and their tensor Table Diffusion tensor imaging (DTI) By the conclusion of this session, metrics were normalized to the corpus callosum changes are indicative of white matter for each specific exam in order to correct for participants should be able to: tract and axonal changes to neural theoretical acquisition discrepancies between studies. structures in the . Degeneration Patient Clinical Information 1) Interpret and analyze MRI DTI of ipsilateral limbic system structures sequences to assess white matter has been demonstrated in temporal tracks lobe , and reorganization of The most significant changes to the Figure 1 contralateral limbic system structures contralateral limbic system white 2) Describe DTI and white matter has been observed following anterior matter structures were an 18 and changes seen in epilepsy and following temporal lobectomy. These post- 16% increase in mean diffusivity (MD) epilepsy surgery operative changes in mesial temporal seen in the and lobe structures have been shown to , respectively. There was 3) Understand changes in contralateral correlate with continued post- also a 9% increase in the MD of the limbic system white matter structures operative seizures and cognitive parahippocampal gyrus. Finally, there following following laser interstitial function. To date, no study has was a 16% increase in the fractional ROI in coronal and axial planes for therapy for selective examined the changes seen in white anisotropy of the white matter tracts Amygdala amygdalohippocampectomy matter structures following laser running through the parahippocampal gyrus. interstitial therapy for selective Figure 2 amygdalohippocampectomy.

Conclusions References Methods Post-operative diffusion MR imaging DTI evaluation was performed in 7 following laser interstitial therapy for Gross DW. Epilepsia. Jul 2011;52 Suppl 4:32-34. patients (median age, 53; age range, selective amygdalohippocampectomy 17-69 years) who underwent pre- and demonstrated increased MD in Concha L, Beaulieu C, Wheatley BM, Gross DW. Epilepsia. May 2007;48(5):931-940. serial post-operative MR imaging as contralateral limbic structures and increased FA in the white matter part of routine follow-up after MR ROI in coronal and axial planes for Nguyen D, Vargas MI, Khaw N, et al. Epilepsy laser guided thermal ablation for tracts of the parahippocampal gyrus. Hippocampus (red) and Parahippocampal Res. May 2011;94(3):189-197. selective amygdalohippocampectomy These changes are indicative of Gyrus (green) for epilepsy. Tensor metrics were structural reorganization of contralateral limbic system structures Winston GP, Stretton J, Sidhu MK, Symms MR, obtain in the subacute period (<3 Duncan JS. Neuroimage Clin. 2014;4:190-200. Results following laser interstitial therapy for months, 36 days median follow-up) after surgery. We evaluated the Preoperative seizure frequency for our selective amygdalohippocampectomy. following limbic system structures on cohort ranged anywhere from 1-2 events/day to 1-2 events/year. the side contralateral to the surgical side: hippocampus, amygdala, Median follow-up was 5 months with a parahippocampal gyrus. range of 4-8 months, and 5 of the 7 patients remained seizure free at time

of follow-up.