- Goodman Campbell Brain and Spine, Department of Neurological Surgery, Indiana University School of Medicine, Indianapolis, Indiana, USA
- Pediatric Neurosurgery, Children's Hospital, Birmingham, Alabama, USA
Aaron A. Cohen-Gadol
Goodman Campbell Brain and Spine, Department of Neurological Surgery, Indiana University School of Medicine, Indianapolis, Indiana, USA
DOI:10.4103/2152-7806.140651Copyright: © 2014 Kovanda JT. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
How to cite this article: Kovanda TJ, Tubbs RS, Cohen-Gadol AA. Transsylvian selective amygdalohippocampectomy for treatment of medial temporal lobe epilepsy: Surgical technique and operative nuances to avoid complications. Surg Neurol Int 12-Sep-2014;5:133
How to cite this URL: Kovanda TJ, Tubbs RS, Cohen-Gadol AA. Transsylvian selective amygdalohippocampectomy for treatment of medial temporal lobe epilepsy: Surgical technique and operative nuances to avoid complications. Surg Neurol Int 12-Sep-2014;5:133. Available from: http://sni.wpengine.com/surgicalint_articles/transsylvian-selective-amygdalohippocampectomy-for-treatment-of-medial-temporal-lobe-epilepsy-surgical-technique-and-operative-nuances-to-avoid-complications/
Background:A number of different surgical techniques are effective for treatment of drug-resistant medial temporal lobe epilepsy. Of these, transsylvian selective amygdalohippocampectomy (SA), which was originally developed to maximize temporal lobe preservation, is arguably the most technically demanding to perform. Recent studies have suggested that SA may result in better neuropsychological outcomes with similar postoperative seizure control as standard anterior temporal lobectomy, which involves removal of the lateral temporal neocortex.
Methods:In this article, the authors describe technical nuances to improve the safety of SA.
Results:Wide sylvian fissure opening and use of neuronavigation allows an adequate exposure of the amygdala and hippocampus through a corticotomy within the inferior insular sulcus. Avoidance of rigid retractors and careful manipulation and mobilization of middle cerebral vessels will minimize ischemic complications. Identification of important landmarks during amygdalohippocampectomy, such as the medial edge of the tentorium and the third nerve within the intact arachnoid membranes covering the brainstem, further avoids operator disorientation.
Conclusion:SA is a safe technique for resection of medial temporal lobe epileptogenic foci leading to drug-resistant medial temporal lobe epilepsy.
Keywords: Epilepsy surgery, medial temporal lobe epilepsy, neurosurgical procedure, selective amygdalohippocampectomy, transsylvian
Drug-resistant epilepsy is defined as recurrent unprovoked seizures refractory to two appropriately selected antiepileptic medication trials.[
Two common procedures are often described in the literature as effective treatments for MTLE. Anterior temporal lobectomy (ATL) has been shown in a randomized, controlled trial to be superior to medical management for relief of MTLE[
Seizure outcomes after SA were previously studied in a retrospective analysis that demonstrated a Class I Engel outcome (patient free of disabling seizures) in 27 of 30 (90%) patients when magnetic resonance imaging (MRI), electroencephalography (EEG), and histopathologic results were concordant.[
Because of the technical complexity of SA, presumed risks, and required familiarity with microsurgical techniques on the part of the surgeon, the use of SA has been limited compared with ATL. There is minimal information available regarding the necessary technical nuances needed to minimize SA complications. The narrow operative corridor through the transsylvian route requires that the surgeon be thoroughly familiar with the surgical anatomy of the region and handling of important adjacent cerebrovascular structures. In this article, we describe the technical aspects of SA, focusing on preoperative evaluation and, more importantly, on surgical anatomy and technique to avoid complications. We describe operative nuances based on the senior author's (ACG) experience with this procedure.
Currently, the American Academy of Neurology recommends that patients with drug-resistant MTLE resulting in disabling complex partial seizures be referred to an epilepsy surgery center.[
All patients should undergo a thorough neurologic examination and have a seizure history documented before surgical consideration. Complex partial seizures are the most common type of seizure resulting from MTLE, and secondary generalization is common.[
Before consideration for surgery, a number of tests may be completed to help define the patient's epileptogenic focus. A high-resolution MRI is necessary, not only for identification of abnormal anatomy, including neoplastic lesions and subtle cortical dysplasia, but also for surgical planning and neuronavigation intraoperatively. In a study of 175 patients who underwent ATL, unilateral hippocampal atrophy on MRI was predictive of postoperative seizure control.[
Concordance of interictal epileptiform discharges and the location of ictal onset on EEG are independent predictors of postoperative seizure control.[
If EEG and/or MRI are unsuccessful in localizing an epileptogenic focus, a nuclear imaging study may be helpful. Single-photon emission computed tomography (SPECT) allows indirect measurement of regional cerebral blood flow.[
Finally, neuropsychological testing is an essential part of the preoperative workup in epilepsy surgery. It provides a baseline regarding the patient's preoperative memory, language, intelligence, attention, frontal lobe function, and visuospatial abilities.[
The intracarotid amobarbital procedure (the WADA test) is a technique used to localize hemispheric dominance. The WADA test also provides insight into the contralateral hemisphere's capability of supporting memory after resection.[
Surgical technique for transsylvian selective amygdalohippocampectomy [ video 1 ]
There are three commonly described approaches for SA. The subtemporal approach was developed in an attempt to avoid unnecessary damage to the lateral temporal lobe.[
The transcortical approach is technically simpler, with the drawback of damage to the lateral temporal neocortex.[
Patient positioning and skull clamp placement
The transsylvian SA (referred to as SA) as described by Yaşargil[
Incision and craniotomy
After completion of the standard pterional incision, the temporalis muscle is reflected in one layer along with the scalp flap. After the bone flap is elevated, the orbital roof is flattened and both the greater and lesser wings of the sphenoid wing are drilled away to the level of the superior orbital fissure. These latter maneuvers minimize retraction on the frontotemporal opercula and enhance more flexible anterior operative working angles through the transsylvian route. Please see
Dural opening and sylvian fissure dissection
The dura is incised in a circular manner and reflected anteriorly. The dural opening should be flush with the newly flattened sphenoid and orbital floor.
The superficial sylvian veins and the divergent frontal and temporal cortical arteries mark the sylvian fissure.[
The dissection of the Sylvian fissure is carried out in a deep to superficial fashion (a-d). A wide opening of the fissure is necessary to obviate the need to fixed rigid retractors. The M1 segment is identified as it curves medially (d-e). Care is taken to minimize retraction on the frontotemporal opercula and manipulation of all the vessels coursing through the fissure. This figure is from The Neurosurgical Atlas, ©Aaron A. Cohen-Gadol, MD, MSc, used with permission.
We do employ the classification schemes designed for estimating the difficulty of fissure dissection before surgery.[
Relevant microsurgical anatomy
The medial temporal lobe surgical anatomy is complicated and must be understood in its entirety before undertaking this procedure to avoid injury to the important adjacent cerebrovascular structures; most at risk are the middle cerebral artery (MCA) branches, the diencephalon/brainstem, the anterior choroidal artery, and the third nerve. The angle of exposure of the ventricle can disorient the surgeon, and therefore neuronavigation is helpful. All relevant boundaries of the structures at risk should be kept in mind. As described by Tubbs et al.,[
Both the head and body of the hippocampus can be identified within the anterior aspect of the temporal horn. The pes of the hippocampus forms the medial border of the anterior temporal horn, whereas the superior border contacts the posteroinferior border of the amygdala. The body of the hippocampus makes up the medial aspect of the temporal horn floor and is bordered laterally by the collateral eminence, which forms the lateral floor of the temporal horn.[
The choroidal fissure, which lies between the choroid plexus (attached to the thalamus) and the fimbria, makes up the medial wall of the posterior two-thirds of the temporal horn.[
Following identification of the M1 and proximal M2 branches and generous exposure of the inferior insula and temporal stem, we make the initial cortical incision in the inferior insular sulcus (10-20 mm), starting just posterior to the temporopolar artery and lateral to the inferior parasylvian vein, which should be coagulated [
Once the temporal stem has been exposed, a 10–20 mm cortical incision is made along the inferior insular sulcus. This incision begins just posterior to the temperopolar artery and lateral to the inferior parasylvian vein (a). This maneuver will allow access to the anterior temporal horn and hippocampus (b) and will create the corridor through which the amygdala and hippocampus are viewed (c). The tip of the temporal horn should be exposed to orient the surgeon regarding the adjacent anatomy. This figure is from The Neurosurgical Atlas, ©Aaron A. Cohen-Gadol, MD, MSc, used with permission.
After removal of the amygdala, cranial nerve III and the medial tentorium become visible through the corresponding arachnoid membranes. Careful identification of these structures is necessary to ensure their preservation. This sketch also contains an overlay of the brainstem and the ventricular system to illustrate the relationship of the surrounding important structures. This figure is from The Neurosurgical Atlas, ©Aaron A. Cohen-Gadol, MD, MSc, used with permission.
The anterior hippocampus is now safely removed in an anterior-to-posterior fashion to the level of the P2 bifurcation (where its tail curves medially) and laterally to the level of collateral eminence [
Once all relevant structures have been identified, the hippocampus can be safely removed in an anterior-to-posterior fashion in two steps. The first step involves removal of the anterior or Pes hippocampus (a) while making an incision just lateral to the choroid plexus. Care should be taken to carefully coagulate the PCA branches to the hippocampus and prevent their avulsion, which could damage the PCA (b). The posterior hippocampus is removed in a second step. Preservation of a small layer of brain tissue along the arachnoid membrane of the basal cisterns ensures the safety of the diencephalic structures (c). This figure is from The Neurosurgical Atlas, ©Aaron A. Cohen-Gadol, MD, MSc, used with permission.
Meticulous handling of the superficial Sylvian veins decreases the risk of venous injury and resultant infarction. There is often a need for extensive microdissection through the sylvian fissure and medial mobilization of the MCA's temporal trunk to create additional operative space for the cortical incision along the inferior parainsular sulcus to enter the ventricle. These maneuvers may be risky if the principles of microsurgery are not carefully followed. Undue retraction on the frontotemporal opercula may lead to language dysfunction in the dominant hemisphere. Perforators from the temporal trunk of the MCA may be injured if these vessels are placed under tension. As discussed above, generous sylvian fissure opening is a key step in SA.
Cerebral Vasospasm: One of the most frequently discussed postoperative complications of SA is cerebral vasospasm resulting from subarachnoid bleeding within the operative field and aggressive manipulation of the corresponding vessels. Intracranial blood flow velocities increase after SA.[
The skill of the surgeon in navigating the complex anatomy of the temporal lobe while minimizing blood loss and vessel manipulation/retraction is paramount.
Visual field deficit: Similarly to ATL, visual field defects are common after SA.[
This potential morbidity should be discussed with the patient before the operation. In addition, care should be taken intraoperatively to minimize retraction on the temporal lobe in an attempt to decrease both the edema and ischemia created within the region. If the surgeon is not intimately familiar with temporal lobe anatomy and does not readily have access to neuronavigation, anteromedial neocortical removal followed by resection of medial structures is a reasonable alternative option.
SA is an effective treatment for drug-resistant MTLE. Through careful dissection with minimal retraction, the transsylvian approach provides an adequate operative field to remove the epileptogenic focus while minimizing damage to the surrounding vascular and cortical structures.
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