Anatomic-radiological feasibility of transorbital magnetic resonance imaging-guided laser interstitial thermal therapy (MRIgLITT) for amygdalohippocampectomy in refractory epilepsy

doi:10.21203/rs.3.rs-5107118/v1

Download PDF

Research Article

Anatomic-radiological feasibility of transorbital magnetic resonance imaging-guided laser interstitial thermal therapy (MRIgLITT) for amygdalohippocampectomy in refractory epilepsy

https://doi.org/10.21203/rs.3.rs-5107118/v1

This work is licensed under a CC BY 4.0 License

Version 1

posted

You are reading this latest preprint version

OBJECTIVE: to study the anatomical feasibility of laser fiber insertion for interstitial thermal therapy via transorbital approach to the temporo-mesial structures (amygdala-hippocampus-parahippocampus complex)

METHODS: Anatomical dissections were performed on two human cadaveric heads via a transorbital approach, in which screws and laser fibers were used for magnetic resonance imaging-guided laser interstitial thermal therapy (MRIgLITT) assisted by neuronavigation. In addition, eight transorbital trajectories were simulated using the transorbital entry points obtained from a cadaveric radiological study of four patients previously operated on for mesial temporal lobe epilepsy.

RESULTS: The placement of all four laser fibers was successfully achieved in the anatomical specimens according to the established plan, with an average vectorial error of 1.3 ± 0.2 mm, and a complete coverage of the amygdala-hippocampus-parahippocampus complex. In addition, safe vascular trajectories were confirmed in the simulations of live patient trajectories. We found an ideal transorbital entry area in the inferolateral quadrant of the orbit, on the lateral wall of the orbit, over the greater wing of the sphenoid, between 15 and 20 mm lateral to the superior portion of the inferior orbital fissure, and between 5 and 10 mm superior to the inferior portion of the inferior orbital fissure.

CONCLUSIONS: Placement of a transorbital laser fiber for MRIgLITT of the temporomesial structures for epilepsy is feasible; however, the small size of the laser fiber-anchoring screw currently precludes its use in clinical practice.

Neurosurgery

amygdalohippocampectomy

epilepsy surgery

laser surgery

transorbital approach

Resective surgery of structures in the mesial temporal lobe is a well-established tool for the treatment of refractory epilepsy, with seizure freedom rates ranging from 44–57%, compared to the worst seizure freedom rates with medical treatment alone of 12–15.3%.^1,2

Extensive surgical resection of the temporal lobe is usually associated with better outcomes in patients with epilepsy. However, these extensive resections are associated with more severe neurological and psychological complications than more selective resections. ^3,4

Following the principles of minimally invasive surgery, interstitial laser ablation of the mesial temporal lobe has gained interest in the field of epilepsy surgery because of its greater selectivity for affected structures and fewer associated neuropsychological complications. ^3,5,6 Multiple studies have been published on laser therapy for selective amygdalohippocampectomy, confirming the advantages of this therapy. ^7–17

In recent years, the possibility of surgically approaching the temporal lobe through an anterior transorbital route has also emerged, offering anatomical advantages in epilepsy surgery owing to its closer proximity to all structures of the mesial temporal lobe. ^18–20 Therefore, we aimed to study the anatomical feasibility of magnetic resonance imaging-guided laser interstitial thermal therapy (MRIgLITT) using the transorbital approach.

Ethical statement

The authors state that every effort was made to follow all local and international ethical guidelines and laws that pertain to the use of human cadaveric donors in anatomical research.

Informed consent was obtained from the patient, and anonymous images of the transorbital surgery were used.

Anatomic dissections

Anatomical dissection of two specimens (four orbits) through the transpalpebral route of the transorbital approach was performed at the Laboratory of Surgical Neuroanatomy (LSNA) of the University of Barcelona (Spain). Specimens were fixed with Cambridge solution and injected with red and blue latex. Computed tomography (CT) and 3 Tesla magnetic resonance imaging (MRI) were performed before and after dissection. Six fiducial screws were placed on the skull surface for neuronavigation.

Planning of the entry point and trajectory of the interstitial diode laser probes was performed for basal CT and MRI studies using the stereotactic software of the Elements Workstation platform (Brainlab, Munich, Germany).

After placing the fiber according to the pre-planned trajectory, the final position of the laser fiber was verified by CT and MRI. The accuracy of reaching the planned targets was confirmed by comparing the radiological errors obtained with the planned trajectory.

Simulation in a clinical environment

The data obtained in the laboratory stage were transferred to a clinical setting using neuroradiological simulations. Preoperative neuroimaging studies (cranial CT and MRI) of four patients who underwent surgery for mesial temporal lobe epilepsy were used.

Eight trajectories were simulated using the orbital entry point results obtained from a cadaveric study on the theoretical placement of laser fibers using the transorbital approach. This served as a preliminary experiment for exploring the clinical applications of this technique. Quantitative and safety analyses of the simulated trajectories were performed to verify that none of the planned trajectories for thermocoagulation affected eloquent neurological areas or vascular structures.

Preliminary considerations

Given the differential quality of the orbital bones compared to those in the cranial vault, we first assessed the feasibility of placing laser fiber anchoring screws in the orbit in this bony region. To this end, a dry skull was employed to simulate the plan previously established in the BrainLab Workstation (Figs. 1A and 1B and Figs. 3A and 3B).

Entry point and trajectory planning

From the planning—both cadaveric and radiological simulations—it became clear (further explained in the next paragraph) that the ideal entry point in the orbit should be in the inferolateral quadrant of the orbit, specifically on the lateral wall, on the greater wing of the sphenoid, between 15 to 20 mm lateral to the upper portion (posteromedial segment) of the inferior orbital fissure and between 5 to 10 mm superior to the lower portion (anterolateral segment) of the inferior orbital fissure (Fig. 1F and 2F). ²¹ A strategy that was proven useful in locating this point was to first define the laterality of the entry in the axial tomography following the inferior rectus muscle to its insertion near the upper portion of the inferior orbital fissure (Fig. 1G) and mark the entry here, lateral to the inferior orbital fissure, in its upper portion, between 15–20 mm. The verticality in the sagittal plane was then defined, positioning it superior to the inferior orbital fissure (lower portion) between 5 and 10 mm (Fig. 1H).

We consider this entry area to be the most appropriate because it allows sufficient medial access to encompass the entire amygdala-hippocampus-parahippocampus complex, lateral enough to minimize compression of the orbital contents, and inferior enough to avoid injury to the vascular structures within the superior orbital fissure, Sylvian fissure, and temporal pole (Fig. 1A, 1C, 1D, and 1E and Fig. 4A and 4B).

The localization of the entry point is a dynamic step that also depends on our goal, which is targeting the amygdala-hippocampus-parahippocampus complex. Both are planned in a coordinated and simultaneous manner (Fig. 1D and 1E), requiring slight adjustments to the orbital entry point and our cerebral target to encompass the largest possible volume of mesial temporal brain structures and ensuring a safe trajectory avoiding eloquent vascular and nervous structures (midbrain, optic tract, and optic radiations—the latter situated above the temporal cerebral ventricle) (Fig. 1-I).

Transorbital approach and placement of laser fiber

The transpalpebral route previously described for the transorbital approach was used. ^18–24 Fig. 2 shows a previously used approach in a patient who underwent open surgery via the transorbital route for temporal pole epilepsy. We have included these images to better demonstrate the anatomical relationships of the approach. The superior and inferior orbital fissures are anatomical landmarks that help orient the entry point in the lateral wall of the orbit, specifically in the greater wing of the sphenoid, aided by the use of stereotaxy (with or without a frame) to find the previously defined entry point during planning (Fig. 2).

We used the BrainLab neuronavigation system to help us to locate a precise entry point previously planned at the workstation. A low-profile drill was then used to perform a minimal craniotomy until the dura mater was reached. The dura mater was opened using a stylet and monopolar coagulation device. The laser probe screw was secured under neuronavigation guidance. Finally, we placed the laser cooling catheter through the screw already fixed to the bone and inserted the laser fiber into the catheter assisted by neuronavigation too, and upon reaching the final target, we tightened the screw to the laser probe (Fig. 3).

The post-procedure average vectorial error was 1.3 ± 0.2 mm, confirmed by CT and MRI.

Once the actual trajectory was fused with real-case imaging techniques, we proved that the planned structures were reached in all four cases with adequate coverage of the amygdala-hippocampus-parahippocampal complex. These trajectories were safe for the vessels in live patient simulations.

When measuring the angles of the screws in relation to the sagittal midline plane in axial cuts of tomographies in the specimen and the radiological simulations (12 in total), all had a medial direction on average measuring 6.6 ± 3.6 degrees. Similarly, all the angles of the screws and radiological simulations (in relation to the Frankfurt plane) in sagittal cuts of tomography had a superior average direction of 4.8 ± 3.5.

Overall, we did not observe any significant difficulties in performing the transorbital approach guided by neuronavigation or in placing each screw in the lateral wall of the orbit. The only issue observed in all cases was severe compression of the orbital contents by the plastic head of the screw due to the short length of the laser probe screws for the orbit, which could be resolved with longer screws (Fig. 5). We further analyze this important difficulty in the discussion section.

Comparison between transorbital approach vs occipital approach

Figure 4 shows a comparison between the transorbital and occipital approaches (both approaches simulated in the same cases) for the laser fiber trajectories used to access the temporomesial structures (amygdala-hippocampus-parahippocampus). This comparison was made as a retrospective simulation of four pre-surgical radiological studies (eight orbits) of patients who underwent temporal lobe epilepsy surgery.

For the occipital approach with the laser fiber to the temporomesial structures, the boundaries are medial: the midbrain with its surrounding vasculature; laterally, the ventricle and optic radiations; and superiorly, the optic tract and optic radiations. This determined a possible entry angle in the axial and sagittal plane on average of 9.12 ± 1.5 ^o and 6.5 ± 1.1 ^o, respectively (Fig. 4C – 4E).

In the transorbital approach, the same boundaries for protection are shared with the occipital approach. In addition, the Sylvian fissure is a superior boundary. Particular attention should be paid to the lateromedial location of the entry point because a medial entry could exert excessive compression of the orbital content. According to previously published data ²⁵, a distance greater than or equal to 15 mm laterally from the upper portion of the inferior orbital fissure or a distance less than 15 mm from the lateral orbital edge to the orbital content is acceptable (Fig. 5A). Taking this into account, the possible entry angles in the axial and sagittal plane averaged 4.8 ± 0.9 ^o and 5.7 ± 0.8 ^o, respectively (Fig. 4A – 4C).

Thus, with the occipital approach, slightly wider possible entry angles are obtained than with the transorbital approach. Therefore, there are more options for possible trajectories to approach the mesial temporal lobe.

In the present anatomical and radiological study, it was anatomically feasible to place a transorbital laser fiber for MRIgLITT with adequate coverage of the amygdala-hippocampus-parahippocampus complex, and we confirmed its safety from a vascular perspective in trajectory simulations in live patients.

The transorbital approach for laser therapy could represent a surgical alternative for patients who cannot achieve safe access to the entire amygdala-hippocampus-parahippocampus complex through an occipital approach. For example, in the case series of Vakharia et al., ²⁶ in 8% of the cases, a much more lateral entry route had to be used (via the posterior portion of the middle temporal gyrus). However, this approach limits the ability to reach the entire temporal-mesial complex appropriately with laser therapy, as medial trajectories generally provide more effective access. ^{10, 27}

Another potential use of transorbital laser MRIgLITT is in the surgical reintervention of failed laser surgeries via the occipital route, in which refractory epilepsy persists. The need for repeat laser surgery to treat refractory epilepsy has been reported in 13–14% of patients. ^1,9 One of the main causes identified was insufficient laser ablation of the uncal and periuncal areas, specifically the amygdala, head of the hippocampus, and entorhinal and perirhinal cortices.^28,29 According to the simulations we carried out for this hypothetical situation, these uncal and periuncal areas could be approached more directly and safely using the transorbital trajectory. This is because the transorbital route provides access through the temporal pole, thus avoiding sensitive structures such as the optic tract and optic radiation (Fig. 6).

However, by better covering the uncal and periuncal areas, which are among the most epileptogenic areas, it would not be possible to reach the rest of the structures of the posterior temporomesial complex with the same laser fiber (the middle and posterior thirds of the hippocampus and parahippocampus). In theory, these would have been previously treated (in failed surgical cases); otherwise, surgery should have been planned with two laser fibers (occipital and transorbital).

Although we could perform transorbital surgery and placement of the anchoring screw quite easily in the anatomical laboratory experiment, we cannot ignore the fact that the very small size of the screw of the current laser fiber creates severe compression of the orbital contents, with more than 15 mm of compression from the lateral orbital rim towards the orbital contents (Fig. 5). Previous laboratory studies have demonstrated a severe increase in intraocular pressure with compression greater than 15 mm from the lateral orbital rim.²⁵ When we simulated a screw size twice the size, we were able to obtain orbital compressions always less than 12.5 mm, which brings the appropriate safety to this approach. We believe that this limitation can be overcome by adapting the screw design to the transorbital region.

It is unlikely that this transorbital approach will replace the occipital approach in laser thermal ablation surgery of the temporomesial structures to treat refractory epilepsy, because of the greater ease and wider possible entry angles of the occipital approach. However, as mentioned above, the transorbital approach may be a good alternative for selected cases in which other approaches are less safe or have failed. Additionally, there is a significant physical limitation (current screw design) of the laser fiber material that prevents its use in clinical practice.

Anatomically, it is possible to place a transorbital laser fiber that allows MRIgLIT of the temporomesial structures for epilepsy surgery. However, there is an important physical limitation: the very small size of the screw of the laser fiber material, which creates severe compression of the orbital contents by the screw head, prevents its use in clinical practice.

CONFLICT OF INTEREST:

The authors declare no competing interests.

ACKNOWLEDGEMENTS:

We thank Mr. Elias Torres for his financial support, which helped us pay for a private editorial for grammatical and editorial reviews of the final report.

Le S, Ho AL, Fisher RS et al (2018) Laser interstitial thermal therapy (LITT): seizure outcomes for refractory mesial temporal lobe epilepsy. Epilepsy Behav. ;89:37–41. 10.1016/j.yebeh.2018.09.040. PMID: 30384097
Kang JY, Wu C, Tracy J et al (2016) Laser interstitial thermal therapy for medically intractable mesial temporal lobe epilepsy. Epilepsia. ;57(2):325–334. 10.1111/epi.13284. PMID: 26697969
Cajigas I, Kanner AM, Ribot R et al (2019) Magnetic resonance-guided laser interstitial thermal therapy for mesial temporal epilepsy: a case series analysis of outcomes and complications at 2-year follow-up. World Neurosurg. ;126. 10.1016/j.wneu.2019.03.057. PMID: 30880205
Gross RE, Willie JT, Drane DL (2016) The role of stereotactic laser amygdalohippocampotomy in mesial temporal lobe epilepsy. Neurosurg Clin N Am 27(1):37–50 PMID: 26615106. PMCID: PMC5502117
Gross RE, Stern MA, Willie JT et al (2018) Stereotactic laser amygdalohippocampotomy for mesial temporal lobe epilepsy. Ann Neurol. ;83(3):575–587. 10.1002/ana.25180. PMID: 29420840. PMCID: PMC5877322
Donos C, Breier J, Friedman E et al (2018) Laser ablation for mesial temporal lobe epilepsy: surgical and cognitive outcomes with and without mesial temporal sclerosis. Epilepsia. ;59(7):1421–1432. 10.1111/epi.14443. PMID: 29893987
Grewal SS, Zimmerman RS, Worrell G et al (2018) Laser ablation for mesial temporal epilepsy: a multi-site, single institutional series. J Neurosurg. ;130(6):2055–2062. doi:10.3171/2018.2.JNS171873. PMID: 29979119
Van Gompel JJ, Burkholder DB, Parker JJ et al (2023) Laser interstitial thermal therapy for epilepsy. Neurosurg Clin N Am. ;34(2):247–257. 10.1016/j.nec.2022.11.005. PMID: 36906331
Tao JX, Wu S, Lacy M et al (2018) Stereotactic EEG-guided laser interstitial thermal therapy for mesial temporal lobe epilepsy. J Neurol Neurosurg Psychiatry 89:542–548
Jermakowicz WJ, Kanner AM, Sur S et al (2017) Laser thermal ablation for mesiotemporal epilepsy: analysis of ablation volumes and trajectories. Epilepsia 58(5):801–810. 10.1111/epi.13715PMID: 28244590. PMCID: PMC5429877
Schmidt D, Stavem K (2009) Long-term seizure outcome of surgery versus no surgery for drug-resistant partial epilepsy: a review of controlled studies. Epilepsia 50:1301–1309. 10.1111/j.1528-1167.2008.01997.x
Liu JT, Liu B, Zhang H (2018) Surgical versus medical treatment of drug-resistant epilepsy: a systematic review and meta-analysis. Epilepsy Behav. ;82:179–188. doi:10.1016/j.yebeh.2017.11.012. PMID: 29576434
Josephson CB, Dykeman J, Fiest KM et al (2013) Systematic review and meta-analysis of standard vs selective temporal lobe epilepsy surgery. Neurology 80(18):1669–1676. 10.1212/WNL.0b013e3182904f82PMID: 23553475
Greenway MRF, Lucas JA, Feyissa AM et al (2017) Neuropsychological outcomes following stereotactic laser amygdalohippocampectomy. Epilepsy Behav. ;75:50–55. 10.1016/j.yebeh.2017.07.033. PMID: 28841472
Helmstaedter C (2013) Cognitive outcomes of different surgical approaches in temporal lobe epilepsy. Epileptic Disord. ;15(3):221–239. 10.1684/epd.2013.0587. PMID: 23899718
Donos C, Rollo P, Tombridge K et al (2020) Visual field deficits following laser ablation of the hippocampus. Neurology. ;94

Egan RA, et al. Visual field deficits in conventional anterior temporal lobectomy versus amygdalohippocampectomy. Neurology. 2000;55:1818–1822.

Chen HI, Bohman LE, Loevner LA, et al. Transorbital endoscopic amygdalohippocampectomy: a feasibility investigation. J Neurosurg. 2014;120(6):1428–1436. doi:10.3171/2014.2.JNS131060. PMID: 24702322.

Chen HI, Bohman LE, Emery L, et al. Lateral transorbital endoscopic access to the hippocampus, amygdala, and entorhinal cortex: initial clinical experience. ORL J Otorhinolaryngol Relat Spec. 2015;77(6):321–332. doi:10.1159/000438762. PMID: 26418017.

De Rosa A, Mosteiro A, Guizzardi G, et al. Endoscopic transorbital resection of the temporal lobe: anatomic qualitative and quantitative study. Front Neuroanat. 2023;17:1282226. doi:10.3389/fnana.2023.1282226. PMID: 37818154. PMCID: PMC10560990.

De Battista JC, Zimmer LA, Theodosopoulos PV, et al. Anatomy of the inferior orbital fissure: implications for endoscopic cranial base surgery. J Neurol Surg B Skull Base. 2012;73(2):132–138. doi:10.1055/s-0032-1301398. PMID: 23542710. PMCID: PMC3424630.

Serioli S, Nizzola M, Plou P, et al. Surgical anatomy of the microscopic and endoscopic transorbital approach to the middle fossa and cavernous sinus: anatomo-radiological study with clinical applications. Cancers (Basel). 2023;15(18):4435. doi:10.3390/cancers15184435. PMID: 37760405. PMCID: PMC10527149.

De Battista JC, Buonanotte CF, Foa Torres GA, et al. Anatomía endoscópica de la unidad estructural Fisura orbitaria inferior - Músculo de Müller en la junción órbito selar medial y su importancia quirúrgica. Rev Fac Cien Med Univ Nac Cordoba. 2017;74(4):372–378. Disponible en: https://revistas.unc.edu.ar/index.php/med/article/view/17043.

Agosti E, Alexander AY, Plou P, et al. 360° around the orbit: key surgical anatomy of the microsurgical and endoscopic cranio-orbital and orbitocranial approaches. Neurosurg Focus. 2024;56(4). doi:10.3171/2024.1.FOCUS23866.

Kim W, Moon JH, Kim EH, et al. Optimization of orbital retraction during endoscopic transorbital approach via quantitative measurement of the intraocular pressure. BMC Ophthalmol. 2021;21(1):76. doi:10.1186/s12886-021-01834-5. PMID: 33557770. PMCID: PMC7871604.

Vakharia VN, Sparks R, Li K, et al. Automated trajectory planning for laser interstitial thermal therapy in mesial temporal lobe epilepsy. Epilepsia. 2018;59(4):814–824. doi:10.1111/epi.14034. PMID: 29528488. PMCID: PMC5901027.

Wu C, Boorman DW, Gorniak RJ, Farrell CJ, Evans JJ, Sharan AD. The effects of anatomic variations on stereotactic laser amygdalohippocampectomy and a proposed protocol for trajectory planning. Neurosurgery. 2015;11(Suppl 2):345–356. doi:10.1227/NEU.0000000000000767. PMID: 25850599.

Galovic M, Baudracco I, Wright-Goff E, et al. Association of piriform cortex resection with surgical outcomes in patients with temporal lobe epilepsy. JAMA Neurol. 2019;76(6):690–700. doi:10.1001/jamaneurol.2019.0204. PMID: 30855662. PMCID: PMC6490233.

Wu C, Jermakowicz WJ, Chakravorti S, et al. Effects of surgical targeting in laser interstitial thermal therapy for mesial temporal lobe epilepsy: A multicenter study of 234 patients. Epilepsia. 2019;60(6):1171–1183. doi:10.1111/epi.15565. PMID: 31112302. PMCID: PMC6551254.

OBJECTIVE

to study the anatomical feasibility of laser fiber insertion for interstitial thermal therapy via transorbital approach to the temporo-mesial structures (amygdala-hippocampus-parahippocampus complex)

METHODS

Anatomical dissections were performed on two human cadaveric heads via a transorbital approach, in which screws and laser fibers were used for magnetic resonance imaging-guided laser interstitial thermal therapy (MRIgLITT) assisted by neuronavigation. In addition, eight transorbital trajectories were simulated using the transorbital entry points obtained from a cadaveric radiological study of four patients previously operated on for mesial temporal lobe epilepsy.

RESULTS

The placement of all four laser fibers was successfully achieved in the anatomical specimens according to the established plan, with an average vectorial error of 1.3 ± 0.2 mm, and a complete coverage of the amygdala-hippocampus-parahippocampus complex. In addition, safe vascular trajectories were confirmed in the simulations of live patient trajectories. We found an ideal transorbital entry area in the inferolateral quadrant of the orbit, on the lateral wall of the orbit, over the greater wing of the sphenoid, between 15 and 20 mm lateral to the superior portion of the inferior orbital fissure, and between 5 and 10 mm superior to the inferior portion of the inferior orbital fissure.

CONCLUSIONS

Placement of a transorbital laser fiber for MRIgLITT of the temporomesial structures for epilepsy is feasible; however, the small size of the laser fiber-anchoring screw currently precludes its use in clinical practice.

The authors declare no competing interests.

Download PDF

Version 1

posted

You are reading this latest preprint version

Anatomic-radiological feasibility of transorbital magnetic resonance imaging-guided laser interstitial thermal therapy (MRIgLITT) for amygdalohippocampectomy in refractory epilepsy

Status:

Version 1

Abstract

Figures

INTRODUCTION

METHODS

Anatomic dissections

Simulation in a clinical environment

RESULTS

Preliminary considerations

Entry point and trajectory planning

Transorbital approach and placement of laser fiber

Comparison between transorbital approach vs occipital approach

DISCUSSION

CONCLUSIONS

Declarations

CONFLICT OF INTEREST:

ACKNOWLEDGEMENTS:

References

References

Additional Declarations

Status:

Version 1