Anteromedial Temporal Lobectomy

Historical Perspective

In 1890 Sir Victor Horsley systematically described the different etiologies of epilepsy and the surgical treatment for each. Sixty years later, the field of epilepsy surgery underwent rapid expansion when Penfield reported efficacy in a case series of 68 patients, 51 of whom underwent anterolateral temporal resections. In 40 cases there was a 50% or greater seizure reduction. In 1951 Bailey and Gibbs described cortical surface electroencephalography for localization of epileptogenic tissue as a means of guiding surgical treatment in psychomotor epilepsy. Then in 1952 Penfield and Baldwin introduced the concept of “incisural sclerosis,” which was believed to be secondary to pressure on medial temporal structures with resultant ischemia. Falconer later popularized the technique of en bloc resection of the hippocampus, which allowed for histopathologic study. Crandall systematically placed depth electrodes in the hippocampi of patients with suspected temporal lobe epilepsy, identifying the ictal onset as hippocampal and correlating this with sclerotic pathology. ^, Despite epileptogenic localization to the medial temporal lobe, the Falconer resection of 5 to 6 cm of the lateral temporal lobe plus the medial structures remained the standard, with small modifications from the 1950s until the 1980s. In 1984 Spencer and colleagues described a modification of the technique that increased the access to medial temporal structures while minimizing the resection to the anterior inferior temporal pole and preserving the superior temporal gyrus (STG). This was based on the predominance of depth-recorded ictal onsets along the entire hippocampus with secondary projection to the lateral cortex, correlative sclerotic hippocampal pathology, and good outcomes with a less disruptive resection. Other modifications have appeared over the years that have aimed at targeting medial structures with minimal disruption of the lateral temporal lobe.

Preoperative Evaluation

Preoperative evaluation may be split into phases, with most centers using either two or three phases of investigation. In three-phase evaluation, the first phase involves inpatient 24-hour continuous audiovisual scalp electroencephalographic (EEG) monitoring, which is used to measure seizure activity and localize epileptogenic tissue. Imaging studies including MRI and positron emission tomography (PET) are used to identify structural and metabolic changes. Single-photon emission computed tomography (SPECT) and magnetoencephalography (MEG) are used primarily in MRI-negative patients, and functional magnetic resonance imaging (fMRI) may be used for functional localization. Neuropsychological testing is then performed to assess baseline IQ, memory, and language to assess the potential side effects of the temporal lobectomy and to guide the extent of resection. Phase 2 involves the Wada test, which is typically performed in patients in whom fMRI for language and memory lateralization is inconclusive. Phase 3 intracranial EEG monitoring is reserved for MRI-negative patients or those in whom noninvasive evaluations are discordant in terms of localization or lateralization of the epileptogenic region. The placement of a subdural grid allows for language mapping, when indicated.

Surgical Decision Making