Surgical approaches for medically refractory mesial temporal lobe epilepsy (MTLE) that previously have been reported include anterior temporal lobectomy (ATL), transcortical selective amygdalohippocampectomy, transsylvian amygdalohippocampectomy, and subtemporaamygdalohippocampectomy.
Each approach has its advantages and potential pitfalls
Minimally Invasive Transpalpebral Endoscopic-Assisted Amygdalohippocampectomy 1).
Since selective amygdalohippocampectomy (SAH) was first reported by Wieser and Yasargil in 1982 2) , there has been a great deal of discussion about optimal surgical procedures, both from the standpoint of seizure outcome and from that of neuropsychological outcome. SAH may be equivalent to anterior temporal lobectomy (ATL) as far as seizure outcome is concerned, and is often superior in terms of neuropsychological performance after surgery.
A recent meta-analysis reported by Josephson et al. revealed superior seizure outcome after ATL compared to SAH 3).
Specifically, the outcomes of the 1,203 patients in the 11 studies demonstrated that participants were statistically more likely to achieve an Engel class I outcome after ATL than after SAH (risk ratio 1.32, 95% confidence interval 1.12–1.57; p < 0.01). The summary risk difference of 8% translated to a number needed to treat 13 for 1 additional patient to achieve an Engel class I outcome after ATL. The author concluded that improved seizure outcome must be balanced against the neuropsychological impact of each procedure.
Because ATL is more extensive and involves the lateral and medial parts of the temporal lobe, it may be predicted that its impact on memory is more important than SAH, which involves resection of medial temporal structures only. However, several studies do not support this assumption. Possible explanations include task-specific factors such as the extent of semantic and syntactic information to be memorized and failure to control for main confounders.
It consists of the removal of the hippocampus, and the amygdalae, which have a role in the processing and memory of emotional reactions, both structures forming part of the limbic system of the brain.
Amygdalohippocampectomy is used only when all other treatment options have failed to resolve the epilepsy. It is an effective treatment for most patients.
Identification of the standard direction for entry into the inferior horn of the lateral ventricle via the Sylvian fissure is an important initial step in performing transsylvian selective amygdalohippocampectomy.
The location of the temporal horn is important to neurosurgeons during procedures such as amygdalohippocampectomy and intraventricular electrode placement for temporal lobe seizure monitoring. However, sometimes the temporal horn is difficult to localize, especially without neuronavigation.
3D magnetic resonance images obtained from 28 patients without intraparenchymal lesions were reoriented to demonstrate all points in the Talairach space of the brain. The limen insulae and the midpoint between the hippocampal sulcus and the innominate sulcus on the coronal slice through the posterior edge of the amygdala were defined as the start and target points, respectively. We evaluated the direction of the vector between these two points and its validity in the brain of 12 patients with temporal lobe epilepsy. The direction of the mean approach vector was 52.4° posteriorly and 16.2° inferiorly. The mean approach vector on the axial plane showed the approximate parallelism with the sphenoid ridge in individual cases. The computer simulation revealed that our average approach vector correctly entered the inferior horn of the lateral ventricle in all temporal lobe epilepsy brains. In vivo morphometry may contribute to the further development of safe and minimally-invasive neurosurgical procedures 5).
6- to 8-cm linear vertical incision extending upward from just anterior to the tragus. An oval trephine (2 x 3 cm) craniotomy is performed flush with the middle fossa floor. Resection of part of the inferior temporal gyrus provide a corridor to the mesial temporal lobe. Identification of the temporal horn of the lateral ventricle can be followed by resection of the parahippocampal gyrus, the amygdala, and the uncus. Segregation of the hippocampus and its subsequent resection in subpial fashion preserved perimesencephalic vasculature. Use of a fine suture for skin closure produced a cosmetic result.
In a 8-year series of 201 patients with a minimum follow-up duration of 2 years, we have observed a low number (1.5%) of complications and a 78% rate of Engel Class I seizure-free outcome. Surgery times were short (average, 2-5 h; range, 2 h 20 min-4 h 10 min) and hospital stays brief (<3 d; range, 1-4 d).
The results suggest that the trephine craniotomy with the inferior temporal gyrus approach has the advantage of minimal invasiveness, including brief operative times and postoperative stays, and also effectively reduces or eradicates medically intractable seizures 6).
The proximal (anterior) transsylvian approach through a pterional craniotomy was developed by the Yasargil in 1967 for the microsurgical treatment of saccular aneurysms of the circle of Willis, frontoorbital and temporobasal arteriovenous malformations, cavernomas, and extrinsic and intrinsic tumors. The acquired positive surgical experiences on this large series enabled the senior author, in 1973, to apply this approach for the selective amygdalohippocampectomy in patients with intractable mesial temporal lobe epilepsy.
The proximal (anterior) transsylvian-transamygdala approach to the mesial temporal structures permits the selective two-thirds resection of the amygdala and hippocampus-parahippocampus in an anteroinferior to posteroinferior exploration axis along the base of the semicircular temporal horn. This strategy ensures preservation of the overlying neopallial temporal convolutions such as the T1, T2, T3, and T4 gyri as well as the related subcortical connective fiber systems and other essential components of the temporal white matter. The application of rigid brain self-retaining retractor systems was strictly avoided during the entire procedure. Computer-assisted navigation was never used. On routine postoperative CT scanning and MR imaging studies, infarction was not observed in any patient. The availability of tractography technology has proven that the connective fiber system around the resected mesial temporal area remains intact.
The surgical outcome and results on neoplastic and vascular lesions of the mesiobasal temporal region have been presented in Volumes II, IIIB, and IVB of Microneurosurgery. The surgical outcomes and results in 102 patients with mesial temporal seizures who underwent surgery performed by the senior author in Zürich have been previously published. In this paper, 73 patients who underwent surgery between 1994 and September 2006 in Little Rock, Arkansas, are presented, and 13 other patients are excluded who underwent surgery after September 2006. Altogether, among 188 patients who underwent surgery, there was no surgical mortality or morbidity, and no neurological deficits, new neurocognitive dysfunction, or impairments of the preoperative incapacities.
The surgical outcome in terms of seizures was rewarding in the majority of patients, particularly in those who exhibited the following irregularities on preoperative investigations: regular local dysfunctions on electroencephalography, dysmorphic changes in the mesiobasal temporal parenchyma on MR imaging studies, and hypometabolism in the anterior third of the temporal lobe on PET studies 7).
SUBTEMPORAL AMYGDALOHIPPOCAMPECTOMY technique has been developed for mesial temporal lobe epilepsy.
The conventional subtemporal approach has been modified to diminish temporal lobe retraction and the risk of damage to the temporal lobe. In the new technique, the surgeons' position has moved from above to below and the approach has been changed from anterolateral to posterolateral, thereby avoiding the voluminous and steeply inclined anterior temporal lobe. By this modified approach, it was unnecessary to remove the roof of the external auditory meatus and it was estimated that both the retraction pressure and the extent of temporal lobe retraction were reduced. To date, surgeons using this approach have operated on four patients with temporal lobe epilepsy whose epileptic foci were in the mesial temporal structure; the inferior temporal gyrus, the temporal tip, the vein of Labbé, and the ventral bridging veins were preserved. After surgery, two patients became completely free of seizures and the other two showed over 90% reduction in seizure frequency without neurological sequelae. Postoperative visual field examination revealed full visual fields without quadrantanopsia. This approach can preserve the temporal stem and lateral temporal lobe, it can be used to remove as much of the posterior hippocampus as necessary, and it can be extended to conventional lobectomy if it is indicated 8).
Park et al report a modification of a surgical technique for AH via the parahippocampal gyrus, in which excision is limited to the anterior hippocampus, amygdala and parahippocampal gyrus while preserving the fusiform gyrus and the rest of the temporal lobe. Because transparahippocampal AH avoids injury to the fusiform gyrus and the lateral temporal lobe, it can be performed without intracarotid sodium amobarbital testing of language dominance and language mapping. Thus the operation would be particularly suitable for pediatric patients in whom intraoperative language mapping before resection is difficult 9)
Presurgical depression, cognitive function, and postsurgical seizure freedom are independent predictors for meaningful improvement in QOL after SAH among the Chinese patients with refractory MTLE. Preoperative evaluation of patients with refractory MTLE should consider the cognitive dysfunction and psychological disorders 10).
Focal resections, including Anterior Temporal Lobectomy and selective amygdalohippocampectomy (SAH), yield 60% to 80% seizure freedom rates in highly selected patients, such as those found to have mesial temporal sclerosis (MTS) on preoperative imaging, but resections are associated with cognitive impairments or focal neurological deficits 11) 12) 13) 14) 15) 16).
Seizure and neuropsychological outcomes did not differ for Selective Amygdalohippocampectomy versus Anterior Temporal Lobectomy for Mesial Temporal Lobe Epilepsy which is similar to most prior studies. Given the theoretical possibility of Selective (AH) sparing language function in patients with epilepsy secondary to mesial temporal sclerosis and the limited high-quality evidence creating equipoise, a multicenter randomized clinical trial is warranted 17).