Indications
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Medial temporal lobe epilepsy associated with mesial temporal sclerosis pathology consisting of neuronal cell loss, gliosis, and synaptic reorganization
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Presumed mesial temporal sclerosis can be determined preoperatively as hippocampal atrophy or increased hippocampal fluid attenuated inversion recovery (FLAIR) signal on magnetic resonance imaging (MRI).
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Lesion-related temporal lobe epilepsy
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Common lesions include vascular cavernous angiomas, focal developmental abnormalities, and low-grade neoplasms.
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Lesions may be associated with hippocampal atrophy, in which case dual pathology exists. In such cases, it is uncertain whether the atrophic hippocampus is nonfunctional and epileptogenic and should be removed, or whether it is capable of normal function and resection would result in cognitive deficits. Neuropsychologic evaluation and the intracarotid amobarbital procedure are performed to address this uncertainty.
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Cryptogenic temporal lobe epilepsy, in which there is no imaged lesion or atrophy and the temporal lobe is identified as the putative epileptogenic region primarily based on intracranial electrophysiology
Contraindications
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Localization of epileptogenesis in the dominant temporal lobe with preserved memory on neuropsychologic testing
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If there is support for memory function on the nondominant side as tested by the intracarotid amobarbital procedure, anteromedial temporal lobe resection (AMTR) still leads to a decline in verbal memory function that is noticeable to the patient.
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If memory function is lacking on the nondominant side as tested by the intracarotid amobarbital procedure, AMTR has the theoretical risk of causing global amnesia.
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Localization of epileptogenesis in the dominant temporal lobe with poor memory on neuropsychologic testing and no or little support for verbal memory on the nondominant side as tested by the intracarotid amobarbital procedure
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In this group, AMTR has the theoretical risk of causing global amnesia.
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Nonepileptic seizures
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All patients should undergo noninvasive continuous audiovisual electroencephalography monitoring even in the presence of seemingly appropriate clinical and radiologic findings to rule out nonepileptic seizures.
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Planning and positioning
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Valproate may lead to bleeding complications. At our institution, we routinely measure prothrombin time, partial thromboplastin time, fibrinogen level, platelet count, and bleeding time. If values are abnormal, we decrease or discontinue valproate and recheck values before surgery.
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Neuronavigation may be used when available.
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Antiepileptic drugs should be taken on the morning of surgery with a small sip of water.
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The patient is positioned supine with a foam wedge or shoulder roll ipsilateral to the side of surgery.
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The head is fixed in a Mayfield head holder, turned to the contralateral side, and extended 50 degrees. The vertex of the head is lowered 10 degrees. Head extension allows the surgeon to view the long axis of the hippocampus with the microscope.
Figure 36-1:
Example of patient position with hair clipped along the planned incision for right AMTR, which is our routine. The position of the frameless stereotactic system’s reference star (Brainlab, Inc., Westchester, IL) for neuronavigation is also shown.
Figure 36-2:
Second example of patient position, this time for left AMTR, with all hair clipped. The head is extended 50 degrees. The skin incision starts at the zygoma anterior to the tragus and curves superiorly and posteriorly. The posterior margin of the incision is a line drawn from the mastoid tip ( M ) to the vertex ( V ). The incision must expose enough of the cranium to remove a bone flap that allows for retraction of the superior temporal gyrus and frontal lobe without compressing brain against the skull edge. The approximate position of the Sylvian fissure ( Syl ) is shown. The superior extent of incision varies based on the patient’s hairline.
Procedure
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