Improving Outcomes in Anteromesial Temporal Lobe Resections - A Demonstration of Resecting the Temporal Piriform Cortex

Summary

Here, we demonstrate an approach to intraoperative neurosurgical guidance in anteromesial temporal lobe resections, specifically highlighting the use of tractography and anatomical masks to aid safe resection of the temporal portion of the piriform cortex - an area increasingly regarded as a crucial surgical target in drug-resistant mesial temporal lobe epilepsy.

Abstract

Anteromesial temporal lobe resection (ATLR) is a useful treatment option for drug-resistant mesial temporal lobe epilepsy (DRmTLE). Growing evidence suggests the piriform cortex plays a crucial role in the generation and propagation of seizures in DRmTLE - and that the resection of the temporal portion of the piriform cortex is associated with significantly improved rates of seizure freedom.

Here, we present the resection of the temporal portion of the piriform cortex in ATLR, using high-resolution preoperative probabilistic tractography algorithms and fused anatomical masks of the structures of interest into the intraoperative neuronavigation and microscope head-up display (HUD).

All patients undergoing comprehensive preoperative assessment and investigations for DRmTLE provided informed, written consent to record an intraoperative video of the procedure. Patients were identified by an expert multidisciplinary team of epileptologists, epilepsy neurosurgeons, neuropsychologists, neuropsychiatrists, and electrophysiologists at a large epilepsy surgery center. The preoperative imaging pipeline included the delineation of critical structures. This included the temporal piriform cortex, and high-resolution probabilistic tractography for essential tracts at risk (e.g., optic radiation and inferior fronto-occipital fasciculus). These were co-registered to the preoperative volumetric neuronavigation scan and uploaded to the intra-operative neuronavigation system.

Presented here is a step-by-step procedure of ATLR, including the resection of the temporal portion of the piriform cortex. The protocol combines Advanced structural and diffusion MR imaging and intraoperative visual aids to integrate anatomical masks of critical grey matter structures and white matter tracts into the surgical workflow in the operating room.

Introduction

Anteromesial temporal lobe resection (ATLR) is the most effective treatment for drug-resistant mesial temporal lobe epilepsy (DRmTLE)^1,2, with 50%-70% seizure freedom rates and relatively low morbidity^3,4,5. The procedure has also been shown to improve quality of life^6,7,8, employment rates⁵, and psychosocial wellbeing⁹.

The canonical ATLR, described ....

Protocol

These methods and protocols are part of an ongoing prospective surgical trial that was approved by the Health Research Authority on 10/09/2020, Research Ethics Committee (REC) London reference: 20/LO/0966. The protocol was prospectively registered: ISRCTN72646265, on 25/09/2020, is available online³⁹, and has been presented at a national conference⁴¹.

The following protocol is applied to all patients undergoing ATLR for DRmTLE in patients 18-70 years old (the age group of patients operated upon for this indication at our specialist adult epilepsy surgery center), all operated upon by the same ....

Results

This protocol and the surgical techniques have been applied within an ongoing study, interrogating the effects of temporal piriform cortex resection and its impact on seizure freedom following ATLR for DRmTLE. The aim of this study is to prospectively determine whether seizure freedom after removal of the temporal piriform cortex does indeed improve seizure freedom in DRmTLE, as the growing body of retrospective data in the literature suggests.

To date, we have employed the described protocol .......

Discussion

This protocol provides a reliable, targeted resection of the temporal portion of the piriform cortex - posited to be a crucial structure in the epileptogenesis and propagation of the mesial temporal lobe epilepsy network^{16,17,24,25,30}.

Components of the standard ATLR technique we perform at our center are adapted from Spencer et al<.......

Materials

Name	Company	Catalog Number	Comments
Brainlab Neuronavigation System	Brianlab, Westchester, IL	https://www.brainlab.com/surgery-products/overview-neurosurgery-products/cranial-navigation/	Intraoperative neuronavigation system
EpiNav Planning Software	N/A	N/A	Clinical Decision Support Tool, for research use, developed in academia at King's College London and University College London
Mayfield clamp	Integra	A1059	Any 3 pin head immobilisation device can be used
Microsurgical instruments			As per local neurosurgical unit
MRI Scanner	GE, Milwaukee, WI, USA	3T MRI GE MR750	Any alternative 3T MRI scanner can be used
MRTrix3	N/A	Reference 47 in the manuscript	MRtrix3 provides a set of tools to perform various advanced diffusion MRI analyses, including constrained spherical deconvolution (CSD), probabilistic tractography, track-density imaging, and apparent fibre density
NORAS coil	NORAS MRI Products	https://www.noras.de/en/mri-produkte/lucy-or-head-holder-8-ch-coil/#infos	Any MRI-safe head immobilisation device can be used
Perforator drill	Stryker	https://neurosurgical.stryker.com/products/elite/	Any alternative neurosurgical perforator drill driver and bit can be used
Sutures - Vicryl Plus 2/-	Ethicon	ETVCP684H	Any alternative suture that the surgeon prefers can be used
Titanium bone plates and screws			As per local neurosurgical unit
Ultrasonic Aspirator	Integra	https://products.integralife.com/cusa-tissue-ablation/category/cusa-tissue-ablation	Any alternative that the surgeon prefers can be used