Extratemporal Nonlesional Epilepsy Surgery

Imaging

Neurophysiologic monitoring with continuous video EEG
- Establish diagnosis of partial epilepsy and localize/lateralize epileptogenic zone
High-resolution MRI
- Extratemporal lesions are best detected on the following MRI sequences: fast fluid attenuated inversion recovery axial, fast T2 axial, T1 sagittal, and magnetization prepared rapid gradient echo coronal sequences
- Improved MRI techniques have eliminated many suspected nonlesional cases
Neuropsychologic evaluation to assess resective risk and localize dysfunctional hemisphere
Functional imaging: PET and postictal and interictal SPECT
- FDG-PET is often poorly localizing in nonlesional extratemporal epilepsy
- Computer-aided subtraction ictal SPECT coregistered to MRI improves the accuracy of intracranial monitoring
MEG is may be used to localize interictal epileptiform discharges
- May provide unique information when other tests are nonlocalizing
Goal of presurgical evaluation: localization hypothesis to explain partial epilepsy based on anatomy, semiology, and neurophysiologic data

Operative Planning

Invasive recordings to prove epileptogenic zone and identify functional cortex (see Chapter 58, Subdural Grid Placement and Chapter 59, Stereotactic Placement of Temporal Depth Electrodes, Figs. 58.1 and 59.1)
Resection of involved tissue without invasive recordings based on semiology, neurophysiologic data, and metabolic imaging (e.g., premotor frontal lobectomy)

Surgical technique covered in Chapters 58 and 59
Resection proceeds based on ictal onset/interictal data identified by the implanted electrodes
Potential neurologic deficits can be predicted based on location of epileptic zone and surrounding eloquent cortex:
- Frontal lobe epilepsy: motor deficits, supplementary motor area syndrome, frontal eye fields, motor speech
- Parietal lobe epilepsy: sensory deficits, expressive speech, neglect syndromes, visual field defects
- Occipital lobe epilepsy: contralateral homonymous hemianopsia, expressive language deficits

Resection After Invasive Electrode Implantation

Preoperative antibiotics/anticonvulsant therapy
Under general anesthesia, the patient is positioned with the head rigidly fixed.
The wires extending in the subgaleal space from the subdural grids and depth electrodes which project through the skin are draped out of the operative field.
The previous incision is reopened.
The bone flap is removed and the dura opened without disturbing the position of the grids.
The location and orientation of the grids is confirmed with the help of the epileptologist.
The epileptogenic zone and functional cortex are verified beneath the corresponding grid contacts and marked.
The epileptic zone in nonlesional epilepsy is resected using subpial dissection techniques.
Careful preservation of the draining cortical veins and arterial supply of adjacent cortex is mandatory.
One of the grid electrodes is sent for routine culture.
After meticulous hemostasis, the dura is closed with 4–0 running Nurolon suture.
The bone flap is replaced and affixed with titanium plates.
A subgaleal drain may be utilized.
The galea is sewn with 2–0 Vicryl and the skin sutured with running 3–0 nylon.
A sterile dressing is applied and the head wrapped.