Indications
- •
Mesial temporal lobe epilepsy without evidence of neocortical involvement is an indication for selective amygdalohippocampectomy.
- •
The decision to proceed with surgery is usually made after medical intractability of epilepsy is established. In many institutions, a paradigm shift toward early consideration of surgery in mesial temporal lobe epilepsy has occurred because of the cognitive side effects of antiepileptic medications and the demonstration of superiority of resection over medical treatment.
- •
Invasive monitoring is often required to determine surgical candidacy and can include (1) foramen ovale electrodes (i.e., to localize the side of the epileptogenic focus), (2) depth electrodes, or (3) subdural grid electrodes.
- •
In many cases, bilateral medial temporal discharges are encountered on electroencephalogram (EEG). Accurate determination of the side of the epileptogenic focus is critical because bilateral amygdalohippocampectomy can be associated with severe and devastating short-term memory deficits.
Planning and positioning
- •
In addition to routine evaluations (patient’s cardiopulmonary status, laboratory values [complete blood count, basic metabolic profile, coagulation profile], chest x-ray, and electrocardiogram), preoperative evaluation includes video EEG, sphenoid or foramen ovale electrodes, and ictal single photon emission computed tomography (SPECT). In the strict sense of selective amygdalohippocampectomy, a Wada test (i.e., intracarotid sodium amobarbital procedure) may be unnecessary, given the absence of significant neocortical resection.
- •
At our institution, frameless stereotactic navigation is used to guide the approach. The most commonly used route—which is the one described here—is the trans–middle temporal gyrus–transventricular route. Other routes include the transsylvian and the subtemporal approaches, with modifications.
- •
The initial target in planning the transcortical dissection should be the temporal horn; registration of the entry point into the sulcus with confirmation of a distance less than 3 cm from the temporal tip is especially important in surgery in the dominant hemisphere.
- •
Whether the patient is placed in a supine or a lateral position, the key element in the positioning chosen is a full and straight lateral position of the patient’s head in the region where the temple is flattest; this positioning is crucial for visualization of the posterior part of the hippocampus while maintaining a safe and adequate trajectory to the rest of the approach.
Figure 37-1:
The patient is placed supine or lateral, if neck rotation would not allow for appropriate head position. The objective is a flat and complete lateral position of the head. A shoulder roll can be helpful in achieving ideal positioning when the patient is supine.
Figure 37-2:
Planning the surgical trajectory from the skin surface down to the temporal horn, which is the cornerstone of the surgical trajectory.
Procedure
