|Year : 2008 | Volume
| Issue : 1 | Page : 94-96
Milind S Sankhe, Venkateswara P Govindappagari
PD Hinduja National Hospital and Medical Research Center, Mahim, Mumbai - 400 016, India
Milind S Sankhe
PD Hinduja National Hospital and Medical Research Center, Mahim, Mumbai - 400 016
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Objectives: To outline the indications, surgical anatomy, approaches and complications. Materials and Methods: We review the anatomy, surgical approaches and possible benefits over wider resections in the temporal lobe. We compare the damage to the temporal lobe by these approaches and review the complications. Conclusions: Selective amygdalohippocampectomy is an effective operation for mesial temporal lobe epilepsy due to mesial temporal sclerosis, particularly on the left side.
Keywords: Mesial temporal sclerosis, selective amygdalohippocampectomy, surgical anatomy, approaches
|How to cite this article:|
Sankhe MS, Govindappagari VP. Selective amygdalohippocampectomy. J Pediatr Neurosci 2008;3:94-6
| Introduction|| |
In the 1950s, Falconer  at the Maudsley Hospital described anatomical temporal lobe resection. This standardized procedure involved the removal of a large amount of temporal neocortex ' en bloc ' with the mesial temporal structures. The resection of a large amount of temporal neocortex has the disadvantage of producing significant neuropsychological deficits, as well as a superior quadrantanopia. For this reason, there has been a tendency to reduce the size of the neocortical resection. When the causative pathology is hippocampal sclerosis, it is likely that the extent of mediobasal resection, rather than the neocortical resection, is the determinate factor in outcome. Amygdalohippocampectomy (AH) was originally developed in epilepsy surgery to spare unaffected brain tissue from surgery, hoping to minimize the cognitive consequences of temporal lobe surgery.
| Indications|| |
Intractable seizures of mesial temporal lobe origin (MTLE) due to mesial temporal sclerosis (MTS) as the substrate is an indication for selective amygdalahippocampectomy (SAH). It is the procedure of choice for speech preservation when dealing with MTS on the left side. The aim of presurgical evaluation is to determine the epileptogenic zone using the imaging and the electrophysiological studies of the brain and the eloquence of the cortex. The epileptogenic zone is the area of the brain which gives rise to seizures and the removal of which results in the patient becoming seizure free. No single preoperative investigation can determine the epileptogenic zone with complete reliability; and even when various investigative modalities are combined, there may be a variable degree of congruence. If neuroimaging demonstrates a well-characterized lesion supported by the clinical features of the seizures and the EEG data, then surgery may be reasonable without additional investigations. However, if the data gathered from the clinical examination, imaging studies and EEG evaluation are conflicting or disparities arise in the presumed localization of the seizure, then further investigations including nuclear imaging and invasive monitoring may be warranted. Neuropsychological evaluation is a must in determining the memory function sustainability and is a crucial investigation before planning the surgery.
| Surgical Anatomy|| |
The hippocampal formation is a composite structure. Its components include Ammon's horn, subiculum, dentate gyrus, subsplenial gyrus, supracallosal gyrus, alveus, fimbria and the fornix. The hippocampal formation, in addition to being a 'C'-shaped arcuate pathway, also has infolding of the gray matter along the curve [Figure - 1],[Figure - 2]. The parahippocampal gyrus (PHG) is transformed from a six-layered cortex to a three-layered cortex along its superior surface just under the hippocampal sulcus. This transition area is the subiculum. On the surface of the subiculum is a layer of white matter, the superficial medullary lamina. As the subiculum curves laterally around the hippocampal sulcus, it is known as Ammon's horn, which is a three-layered cortex; and it continues medially. An infolding of the gray matter just above the hippocampal fissure is the dentate gyrus. Choroidal fissure found on the superior surface of the hippocampus formation separates the temporal horn from the perimesencephalic cistern. The alveus is the collection of white matter fibers on the lateral and superior surface of the Ammon's horn.
Upon entry into the temporal horn, the obvious structure is the Ammon's horn with the underlying three-layered cortex of the hippocampus. Medial to the Ammon's horn is the hippocampal sulcus with the dentate gyrus lying just above the sulcus and the subiculum underneath the sulcus. The most anterior portion of the hippocampus formation is the enlarged and lobulated 'pes hippocampi.' The amygdala is anterior to the pes hippocampi at the tip of the temporal horn. The anteromedial portion of the PHG is called the uncus, which is separated from the cisternal structures by the pia mater [Figure - 3].
| Approaches|| |
Various approaches have been described to enter the temporal horn. SAH removes the mesial temporal structures via either trans-sylvian, transcortical or trans-sulcal microsurgical approach with the goal of sparing temporal neocortex and reducing any possible neuropsychological deficits [Figure - 4].
- Transventricular approach - Niemeyer 
Through the middle temporal gyrus
Through the superior temporal sulcus
- Trans-sylvian approach - Weiser and Yasargil 
- Subtemporal transparahippocampal approach - Park 
The aim of AH is reportedly to remove the amygdala, anterior hippocampus, parahippocampal gyrus and the subiculum, which acts as a hyperexcitable fringe and hence as an amplifier.
Additionally, it is recommended that the posterior hippocampus (at the level of the ascending tail), beyond the beginning of the P-3 segment of the posterior cerebral artery, is usually left behind. Dissection posterior to the posterior rim of the cerebral peduncle risks damage to the lateral geniculate body and the geniculocalcarine radiations of Meyer.
| Discussion|| |
En bloc anterior temporal lobectomy (ATL) in which the lateral neocortex and medial temporal structures are removed at a standard distance posterior to the temporal pole is a safe and effective surgical treatment for intractable temporal lobe epilepsy in trained hands.  However, it has been considered desirable that when the focus originates in the medial temporal lobe, the lateral neocortex should be preserved to limit postoperative neuropsychological deterioration. Hence SAH was first proposed by Niemeyer in 1958  and re-popularized by Yasargil in 1984. , There is controversy, however, as to when the procedure is indicated. It is reported that patients have better neuropsychological and psychosocial outcomes after SAH than after ATL  but this is controversial.  The reason for controversy regarding postoperative changes in memory and cognition may be related to the length of time between surgery and assessment. The relative contributions of the medial structures and the lateral neocortex to memory are not fully understood but probably both have a role. Although assessment early in the postoperative period suggested that SAH conferred no advantage over ATL,  later postoperative assessment suggests that left SAH was significantly superior to ATL in terms of verbal IQ and nonverbal memory gains but not significantly different in terms of performance IQ and language (fluency). Verbal memory declined after both surgeries but to a greater extent after ATL. It is interesting to note that both surgeries resulted in a decline in verbal memory. It has been suggested that verbal memory is dependent on both the medial temporal lobe structures and the lateral neocortex,  and therefore it is possible that damage to the white matter of the anterior temporal lobe after SAH has resulted in impaired lateral neocortical function. Contrary to belief that in general, the larger the resection, the better the outcome, the seizure outcome is notably independent on the extent of removal of the amygdala or hippocampus.  It might suffice to resect most of the epileptogenic focus together with disruption of the anterior commissure and uncinate fasciculus, which are the main propagation pathways in mesiolimbic seizures. Temporal lobe damage as a result of surgery was noted to a variable degree in most cases and was more extensive in the patients operated upon via the transcortical route in comparison to the patients operated via the trans-sylvian route. The damage to the cortex is significant in the middle temporal gyrus. Although the trans-sylvian route usually does not damage the cortex, it does damage the temporal stem, particularly disconnecting the superior temporal gyrus. The damage may be variable in extent. In contrast, the subtemporal transparahippocampal AH has an important advantage in that the operation spares the temporal stem and the remaining temporal gyri, although some retraction injury may occur to the anterior fusiform gyrus and the inferior temporal gyrus.
As for seizure cure, there is no significant difference between the AH group and the ATL group. The overall success rate was 88% for SAH and 82% for en bloc ATL. 
| Complications|| |
Complications specific to the operation and approaches include:
- Contralateral incomplete quadrantanopia
- Peri-sylvian hematoma
- Vasospasm has also been reported
- Hemiparesis due to injury to the anterior choroidal artery and the midbrain, particularly if the pia is breached
- Overzealous dissection and handling of the occulomotor nerve may lead to third nerve paresis
| Conclusion|| |
Amydgdalohippocampectomy is a safe and effective surgical treatment for intractable temporal lobe epilepsy in trained hands when the focus originates in the medial temporal lobe. The operation is particularly useful when the focus is on the left side. It helps preserve the lateral neocortex to limit postoperative neuropsychological deterioration.
| References|| |
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[Figure - 1], [Figure - 2], [Figure - 3], [Figure - 4]