Anteromesial Temporal Lobectomy for Medically Intractable Temporal Lobe Epilepsy: An Operative Study

[Instructor] Anteromesial temporal lobectomy is the most widely performed surgery for treatment of medically refractory temporal lobe epilepsy, yielding excellent seizure-free outcomes and significant improvements in quality of life. There is variability in techniques for performing temporal lobe resections, ranging from a more extensive resection of lateral and mesial structures, or corticoamygdalohippocampectomy, to a more limited resection of mesial structures via a smaller surgical window or a selective amygdalohippocampectomy. This may be further influenced by underlying pathology, baseline neurocognitive function, and surgeon preference. Common temporal lobe pathologies that warrant consideration of temporal lobectomy include mesial temporal sclerosis, focal cortical dysplasia, neoplastic or vascular lesions, and non-lesional cases where electrocorticography studies may also be a guiding factor. Here, we review surgical highlights of the standard anteromesial temporal lobectomy procedure, including resection of the mesial structures. The patient is positioned supine on the OR table with the head rotated toward the contralateral shoulder and extended slightly to facilitate visualization along the anteroposterior axis of the mesial structures. Depending on surgeon preference, the head may or may not be rigidly fixed in a head frame. A reverse question-mark-type incision is made, extending from the zygoma inferiorly back toward the posterior limit of the ear and up to a few centimeters above the superior temporal line dorsally. The scalp flap is elevated, with preservation of the underlying temporalis muscle. The muscle may be opened in a T-shaped or a curvilinear fashion. With a T-shaped opening, the bisection is made down to the level of the zygoma, and a small cuff is left superiorly to allow for later closure of the muscle. This also reduces muscle bulk anteriorly in the working field. Electrocautery is minimized and the deeper fascia maximally preserved in order to maintain blood supply and reduce muscle atrophy. A frontotemporal craniotomy is made to provide access down to the middle cranial fossa and anteriorly to the keyhole, with minimal exposure of the supersylvian frontal operculum. Here, burr holes are placed at the zygoma, keyhole, and posteriorly, allowing for multiple access points to also strip the dura off the innercortical table. This may be especially important in older patients and those who have undergone stereo-EEG surgery with resulting dural adhesions. The bone flap is carefully removed and major dural vessels are gently cauterized. If needed, additional bony removal may be performed along the sphenoid wing and the inferior squamous temporal bone so that the opening is optimized further. Exposed air cells should be meticulously waxed off to avoid CSF leak complications. Tack-up sutures may also be placed at this time. The dura is opened in curvilinear fashion and reflected anteriorly. Retraction sutures are placed. The lateral neocortical resection is performed. This starts with a superior and posterior corticectomy. The posterior corticectomy in a typical non-dominant, right-sided resection is made 5.5 to six centimeters from the temporal tip, as measured along the middle temporal gyrus. On the language-dominant side, a more conservative measurement of four to 4.5 centimeters is used. The large draining vein of Labbe should also be identified and preserved. The posterior cut is carried down to the middle fossa floor to visualize the tentorium. A superior cut is made along the superior temporal gyrus and carried forward to the temporal pole. Sub-pial dissection and aspiration is performed to best visualize the anatomy and pial planes throughout the case. Aspiration of the superior temporal gyrus exposes the underlying insula and MCA branches, which should be carefully preserved. Anteriorly, the superior temporal gyrus should be followed into the temporal pole, and this tissue should be removed in sub-pial fashion as well. The inferior circular sulcus is identified, and the white matter at this level may be followed into the temporal stem, often taking a 30 to 45-degree angle depending on the anatomy here. The temporal horn of the lateral ventricle is often encountered, typically further posteriorly, and a cottonoid patty can be inserted to prevent blood from entering the ventricular system. The hippocampus can often be visualized with a small intervening lateral ventricular sulcus, and the more laterally-situated collateral eminence, the bulge lateral to the hippocampus, which is a prominence caused by the collateral sulcus underneath. This is a safe landmark that keeps a surgeon above the tentorium. As one completes the posterior disconnection laterally around and down to the middle fossa floor, the cut goes across the lateral occipital temporal sulcus and fusiform gyrus to meet up at the collateral sulcus. At this point, the collateral eminence and sulcus may be followed anteriorly to join with the anterior disconnected cut. The lateral neocortical resection and pial disconnection is completed on block. Cortical draining veins along the temporal pole are carefully inspected and coagulated as appropriate. This tissue is oriented with a few staples, anteriorly, posteriorly, and dorsally, and sent for pathology. The mesial resection begins by opening up the temporal horn to expose the hippocampus. Inside the ventricle, the hippocampal head and body are identified along the inferior aspect in the floor of the ventricle. The choroid plexus and the inferior choroidal point are noted behind the head of the hippocampus, and a cottonoid is placed here to protect the anterior choroidal artery entering the choroidal fissure. Anterior and superior to the hippocampal head is the amygdala separated by a small sulcus, the uncal recess, which is divided. The amygdala extends superiorly to the striatum with no clear demarcation, and therefore its superior extent of resection is limited based on a line drawn from the inferior choroidal point to the MCA, or M12 bifurcation, effectively within the same plane as the choroidal fissure itself. The amygdala resection is carried mesially through the anterior aspect of the uncus to reach the mesial pia, which should be preserved. The parahippocampal gyrus is aspirated next in sub-pial fashion to undermine the hippocampus and allow it to mobilize and rotate outwardly, following disconnection of its posterior limits somewhere along the tail. Along its mesial length, the alveus and fimbria of the fornix are divided down to the pia. The perforating vessels of Uchimura arising mesially from the posterior cerebral artery as small arterial branches supplying the hippocampus are coagulated and sharply divided as the hippocampal body is further dissected laterally. In many cases, the hippocampus can then be peeled off the hippocampal sulcus using a Penfield instrument. When firmly adherent and stuck, it may be resected in piecemeal fashion using cautery and suction. It should be noted that samples of the amygdala and hippocampus are routinely sent to pathology as well. Finally, the residual tail of the hippocampus is further resected posteriorly up to the point of curvature behind the midbrain. The remaining posterior uncus is resected in sub-pial fashion. The tentorial edge and oculomotor nerve should now be in view, often with the posterior cerebral artery visualized further posteriorly. Meticulous hemostasis is maintained throughout the procedure. The dura is closed primarily and can be reinforced with the dural substitute onlay as well. Tack-up stitches are placed if not done already, and the bone flap is replaced. The temporalis muscle is reapproximated and a subgaleal drain is placed. Following skin closure, a sterile dressing with head wrap may be applied to further minimize subgaleal collections. Postoperatively, the patient is monitored in a neuro step-down unit or in the pediatric population in an ICU setting, a short course of steroids up to 48 hours and resumption of the patient's home anti-epileptic medication regimen is done to optimize immediate postoperative recovery. This is a typical postoperative CT obtained in the immediate postoperative period. There is no evidence of hematoma or other postoperative complications. Here, we see pre- and postoperative MRI highlighting successful removal of the right temporal lobe, including the mesial structures. The success of this procedure has been documented extensively in the literature with the most important goal being seizure freedom. Two randomized controlled trials have shown significant improvement in seizure freedom, as well as quality of life for patients after undergoing this procedure as compared to patients only receiving medical therapies. Suboptimal or adverse outcomes occur as a function of manipulating the tissue in and around the temporal lobe. An upper quadrant visual field deficit occurs in 1/3 to 1/2 of cases, which patients can often compensate for. It is best to minimize retraction along the roof of the temporal horn and consider using tractography imaging with navigation if one aims to reduce this risk. There is also a risk of naming deficit, especially seen after a dominant temporal resection. This requires extensive baseline neuropsychological testing to counsel patients accordingly. The figures shown here represent additional important findings related to the standard temporal lobectomy described in this video. In Figure 3, these authors compared a standard resection to a more selective amygdalohippocampectomy across 621 patients with hippocampal sclerosis after over two decades of follow-up. Long-term seizure outcome was significantly more favorable with the standard resection. Thus, more extensive tissue resection appears to correlate with improved outcomes. In Figure 4, we see neurocognitive outcomes found in patients after undergoing an alternative surgical approach called stereotactic laser ablation. Here, the temporal lobe tissue is cauterized focally with thermal energy instead of being directly resected. Although the seizure-free outcome is lower in this cohort due to less disruption of surrounding fibers, this consequently preserves or even improves function across multiple domains. In conclusion, medically refractory epilepsy remains a major healthcare burden globally, with temporal lobe epilepsy being the most common etiology. Through interdisciplinary conferences at large tertiary medical centers, we can identify appropriate pathologies for this procedure based on electrographic information, imaging, semiology, and other medical and social factors. Implementing the methodology described here for anteromesial temporal lobectomy can result in excellent seizure-free outcomes for patients. Of course, technical nuances exist depending on patient anatomy, as discussed here. Thank you for watching.