Minimally invasive surgical approaches for temporal lobe epilepsy

Abstract

Surgery can be a highly effective treatment for medically refractory temporal lobe epilepsy (TLE). The emergence of minimally invasive resective and nonresective treatment options has led to interest in epilepsy surgery among patients and providers. Nevertheless, not all procedures are appropriate for all patients, and it is critical to consider seizure outcomes with each of these approaches, as seizure freedom is the greatest predictor of patient quality of life. Standard anterior temporal lobectomy (ATL) remains the gold standard in the treatment of TLE, with seizure freedom resulting in 60-80% of patients. It is currently the only resective epilepsy surgery supported by randomized controlled trials and offers the best protection against lateral temporal seizure onset. Selective amygdalohippocampectomy techniques preserve the lateral cortex and temporal stem to varying degrees and can result in favorable rates of seizure freedom but the risk of recurrent seizures appears slightly greater than with ATL, and it is not clear whether neuropsychological outcomes are improved with selective approaches. Stereotactic radiosurgery presents an opportunity to avoid surgery altogether, with seizure outcomes now under investigation. Stereotactic laser thermo-ablation allows destruction of the mesial temporal structures with low complication rates and minimal recovery time, and outcomes are also under study. Finally, while neuromodulatory devices such as responsive neurostimulation, vagus nerve stimulation, and deep brain stimulation have a role in the treatment of certain patients, these remain palliative procedures for those who are not candidates for resection or ablation, as complete seizure freedom rates are low. Further development and investigation of both established and novel strategies for the surgical treatment of TLE will be critical moving forward, given the significant burden of this disease.

Keywords: Gamma knife; Laser ablation; Responsive neurostimulation; Selective amygdalohippocampectomy; Temporal lobectomy.

Copyright © 2015 Elsevier Inc. All rights reserved.

Figures

Fig. 1

Microsurgical anatomy of the temporal lobe. A) Lateral view of the left hemisphere. The lateral surface of the temporal lobe consists of three parallel gyri: superior, middle, and inferior temporal gyri. These gyri are separated by the superior and inferior temporal sulci. The lateral parietotemporal line (red dashed line), an imaginary line connecting the preoccipital notch and parietooccipital sulcus, separates the temporal and occipital lobes, and the occipitotemporal line (blue dashed line), an imaginary line connecting the posterior margin of the sylvian fissure with lateral parietotemporal line, separates the temporal and parietal lobes. B) Inferior view of the left temporal lobe. The basal surface of the temporal lobe consists of, from lateral to medial, the inferior margin of the inferior temporal gyrus, the fusiform gyrus, and the parahippocampal gyrus. The fusiform gyrus is separated laterally from the inferior temporal gyrus by the occipitotemporal sulcus and medially from the parahippocampal gyrus by the collateral posteriorly and rhinal sulci anteriorly, which are not continuous in every case. The basal parietotemporal line connecting the preoccipital notch and inferior end of parietooccipital sulcus separates the temporal and occipital lobes at the basal surface. C) The superior view of the left temporal lobe. This surface facing the sylvian fissure is divided, from anterior to posterior, into three portions: the planum polare, the anterior transverse temporal gyrus, referred to as the Heschl's gyrus, and the planum temporale containing the middle and posterior transverse temporal gyri. D) Enlarged view of the anterior and middle segments of the medial temporal region. The anterior segment of the uncus faces the carotid cistern, and the posterior segment faces the crural cistern and the cerebral peduncle. The uncal apex is positioned lateral to the oculomotor nerve. The cortical component of the middle medial temporal region formed by the parahippocampal gyrus faces the midbrain across the ambient cistern. E) The medial temporal region with hippocampus and dentate gyrus having been removed while preserving the fimbria and the choroid plexus attached along the choroidal fissure. The amygdala forms the anterior wall of the temporal horn and fills most of the anterior segment of the uncus. The inferior choroidal point, located at the lower end of the attachment of the choroid plexus in the temporal horn, is positioned behind the head of the hippocampus, anterior to the lateral geniculate body, and lateral to the posterior edge of the cerebral peduncle. Amb.: ambient; Ant.: anterior; Calc.: calcarine; Car.: carotis; Cent., central; Chor.: choroidal; Cist: cistern; Coll.: collateral; CN III: oculomotor nerve; Fiss.: fissure; Gen.: geniculate; Hippo.: hippocampus; Inf.: inferior; Lat.: lateral; Mid.: middle; Occ.: occipital; Parahippo.: parahippocampal; Par.-Occip.: parietooccipital; Par.-Temp.: parietotemporal; Ped.: cerebral peduncle; Post.: posterior; Seg.: segment; Sulc.: sulcus; Sup.: superior; Temp.: temporal; Tent.: tentorial; Tr.: tract; Trans.: transverse; Uncin.: uncinate. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.) Figure and legend modified and reproduced with permission from Kucukyuruk et al. [24] distributed under the Creative Commons Attribution License.

Fig. 2

Demonstration of anterior temporal lobectomy for mesial temporal lobe epilepsy. A, B) Preoperative T2-weighted coronal (A) and axial (B) MRI showing increased T2 signal, decreased size, and diminished cytoarchitecture of the left hippocampus, consistent with mesial temporal sclerosis. C, D) Preoperative T2-weighted coronal (C) and axial (D) MRI demonstrating the resection cavity after left anterior temporal lobectomy. The resection involves the anterior hippocampus to the level of the tectal plate, the amygdala, and an approximately 4-cm resection of the anterolateral temporal neocortex, including the middle and inferior temporal gyri.

Fig. 3

Microsurgical approaches for selective amygdalohippocampectomy. Three main approaches are shown for selective resection of the mesial temporal structures while preserving lateral temporal neocortex. The transsylvian approach includes microsurgical splitting of the sylvian fissure and traversing a portion of the temporal stem, the transcortical approach proceeds through a limited lateral temporal corticectomy while the subtemporal approach involves gentle elevation of the temporal lobe to identify and enter the collateral sulcus. L: left; R: right.

Fig. 4

Gamma knife stereotactic radiosurgery planning in a patient with mesial temporal lobe epilepsy. On axial (A), coronal (B), and sagittal (C) T1-weighted MRI images, treatment is planned at the mesial temporal structures, with 50% isodose line shown in yellow, 20% isodose line displayed in green, and crosshairs approximating the center of the target. Care is taken to limit the radiation dose to the optic apparatus and brainstem. A: anterior; L: left; P: posterior; R: right. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Fig. 5

Development of radiologic changes in a patient with mesial temporal lobe epilepsy treated with a 24-Gy dose gamma knife stereotactic radiosurgery. FLAIR (A–E) and T2 (K–O) hyperintensity appeared within the medial temporal lobe beginning by the 10th postoperative month and peaked in intensity at 12 months, corresponding to a decline in the proportion of patients experiencing complex partial seizures. Contrast enhancement (F–J) followed a similar time course, except that it preceded T2 changes and diminished quickly after months 10–12. Enhancement was typically ring-enhancing and centered over the target region. Figure and legend reproduced with license and permission from Chang et al. [73].

Fig. 6

Stereotactic laser thermo-ablation in mesial temporal lobe epilepsy. A–C) T1-weighted periprocedural MRI coronal (A), axial (B), and sagittal (C) images showing laser probe placement along the axis of the left hippocampus, prior to thermo-ablation in a patient with mesial temporal lobe epilepsy. D–F) Contrast-enhanced T1-weighted MRI coronal (D), axial (E), and sagittal (F) images after thermo-ablation of mesial temporal lobe structures, with contrast enhancement observed in the region of ablation. A: anterior; L: left; P: posterior; R: right.