The Role of Stereotactic Laser Amygdalohippocampotomy in Mesial Temporal Lobe Epilepsy

Abstract

Stereotactic laser amygdalohippocampotomy (SLAH) uses laser interstitial thermal therapy guided by magnetic resonance thermography. This novel intervention can achieve seizure freedom while minimizing collateral damage compared to traditional open surgery, in patients with mesial temporal lobe epilepsy. An algorithm is presented to guide treatment decisions for initial and repeat procedures in patients with and without mesial temporal sclerosis. SLAH may improve access by medication-refractory patients to effective surgical treatments and thereby decrease medical complications, increase productivity, and minimize socioeconomic consequences in patients with chronic epilepsy.

Keywords: Ablation; Anterior temporal lobectomy; Laser; Memory; Mesial temporal lobe epilepsy; Mesial temporal sclerosis; Neuropsychology; Selective amygdalohippocampectomy.

Fig. 1

Effects of temperature on tissues. Both laser ablation and RF ablation have effects on tissues as a function of temperature. Lower than 44ºC, tissue effects are absent irrespective of time. Damage is time dependent between 44ºC and 59ºC; damage occurs as a function of time and temperature as predicted by the Arrhenius equation. This is the important temperature range for controllable lesions using LITT. At 60ºC or greater, tissue coagulation is instantaneous; these temperature effects occur close to the laser fiber diffuser tip. Instant vaporization occurs greater than 100ºC; the system is generally set to turn off automatically if the temperature near the tip reaches 90ºC to prevent damage to the tip.

Fig. 2

Decision tree for SLAH in patients with MTLE. All patients undergo comprehensive diagnostic evaluation for epilepsy, including history, seizure semiology, MRI, fluorodeoxyglucose-PET, LTVM, and neuropsychological testing (NP). Other diagnostic tests are performed as indicated. Therapeutic decision making occurs during comprehensive epilepsy surgery conference. This decision tree is a general guide to determine surgical candidacy and may vary from case to case depending on individual patient information. ^a Depicted is the indication for Wada testing for the purpose of determining contralateral memory performance, that is, nondominant associated visual memory when the focus is on the dominant side, and vice versa. However, Wada testing is almost always performed with bilateral carotid amobarbital injections, to also determine ipsilateral memory performance that may factor into decision making as well.

Fig. 3

Hardware components for SLAH using Visualase laser thermal therapy system using different ste-reotactic methods. (A) Fifteen-Watt 980-nm diode laser energy is directed along a 400-μm core silica optical fiber that terminates in a circumferential diffusing tip (red). This fiber optic is housed within a 1.65-mmdiameter saline-cooled polycarbonate cooling cannula (bottom). A threaded plastic bone anchor (top right) and stiffening stylet (middle) are used to stereo-tactically deliver the device to brain structures. (B) Stab incisions and 3.2-mm twist drill holes are made using a stereotactic headframe. Anchor bolts are threaded into twist holes under stereotactic control; Visualase laser applicators are passed through bolts, secured, and flagged with sterile adhesive strips. (C) Alternative direct real-time MRI-guided placement of Visualase laser applicator via an MRI guidance miniframe (SmartFrame, MRI Interventions, Irvine, CA) within an MRI suite. ( From Willie JT, Tung JK, Gross RE. MRI-guided stereotactic laser ablation. Chapter 16. In: Golby AJ, editor. Image-guided neurosurgery. Boston: Academic Press; 2015. p. 380; with permission.)

Fig. 4

Imaging associated with a case of SLAH for right MTS. Preablation diagnostic MRI (coronal T2 and fluid-attenuated inversion recovery [FLAIR], first column) show typical features of right hippocampal atrophy and mildly increased T2 and FLAIR intensity. Coronal and axial T1 with NeuroQuant (CorTechs Laboratory, San Diego, CA) analysis (second column) with colorized mesial temporal structures (amygdala in blue, hippocampus in brown) further exhibit right MTS. Coronal and axial FDG-PET images (third column) emphasize reduced hypome-tabolism of right mesial temporal structures. Visualase workstation screenshots during SLAH procedure (fourth column) show real-time axial MR gradient-based T-map during LITT in amygdala region (above) and combined irreversible damage estimate encompassing mesial temporal structures at time of procedure completion (below). Immediate postablation MR images show features after LITT including T2 (coronal) and FLAIR (axial) hypointense rings (fifth column), and peripheral contrast enhancement surrounding T1 hypointensity (coronal/sagittal gadolinium [Gd]-contrasted T1 images, sixth column).

Fig. 5

Decision tree for further surgical treatment in non–seizure-free patients after SLAH. This is a guide to our decision making process in patients who are not seizure free after SLAH. Decision making may vary in a case-by-case manner depending on individual information and preferences.