10 Frontal Lobe Resection in Refractory Epilepsy

10.1055/b-0040-177291

10 Frontal Lobe Resection in Refractory Epilepsy

Arthur Cukiert

Abstract

Frontal lobe resection is the second most frequently performed resective procedure in refractory epilepsy patients. The frontal lobe encompasses several potentially epileptogenic areas that could give rise to different types of seizures. Surgical results are better in patients with positive MRI findings. Invasive recordings using stereoencephalography, subdural electrodes, or combinations of both are usually needed in patients with normal MRI. Patients with normal MRI usually require more extensive cortical resection. In this chapter, we describe the technical aspects relevant to frontal lobe resections, including anatomical considerations, mapping techniques, and how to avoid unexpected neurological deficits.

10.1 Introduction

Frontal lobe epilepsy represents the second most frequently refractory epileptic syndrome surpassed only by temporal lobe epilepsy. Although known as a single lobe from an anatomic perspective, there are different “frontal lobes” from an epilepsy point of view. Specific frontal regions yield very different seizure types and clinical behavior. Thus, the motor cortex originates motor simple partial seizures, the dominant frontal opercular cortex (Broca area) originates aphasic seizures, the frontal eye-field gives rise to seizures with head and eye deviation, the frontal lateral convexity yields complex partial seizures, the supplementary motor area gives rise to postural seizures, the mesial prefrontal cortex originates hypermotor seizures, the frontobasal cortex originates olfactory seizures, and the orbitofrontal cortex might originate complex partial seizures. Although the primary motor cortex is considered part of the frontal lobe, the frontal primary motor and somato-sensitive parietal areas should be dealt with as a separate lobe (the “rolandic lobe”) as far as epilepsy is concerned.

10.2 Patient Workup and Outcome

Frontal lobe resections comprised 10% of the patients submitted to surgery in our nearly 2,000-patient surgical series (▶Fig. 10.1). Surgical outcome was clearly related to the presence of lesions on MRI ¹ : 92% of the patients with focal lesions on MRI were rendered seizure free after surgery, compared to 66% of the patients with normal MRI. Although the outcome of patients with normal MRI was inferior to those with positive scans, that was still a much superior result compared to medication only (all these patients had refractory epilepsy). In a recent meta-analysis, ² both the presence of a lesion on MRI and its complete surgical removal were the most relevant positive predictors for good outcome regarding seizure control in this patient population.

**Fig. 10.1** Summary of the epilepsy surgery series. Frontal lobe resections made up to around 10% of the patients.

Some lesions like cavernoma or small benign tumors might need small resections, but patients with normal MRI most often would need large resections to adequately disrupt the epileptic network. The best scenario would be to be able to resect the lesional area (if any), the ictal onset zone, the area from where seizures could be elicited by stimulation, and the interictal spiking region. These resections are often restricted by the presence of eloquent cortex within the potential resective area. It is clear, though, that if there is an epileptogenic lesion on MRI, the resective procedure should at least remove the entire lesion whenever possible.

Common etiologies found in patients with refractory frontal lobe epilepsy include cortical dysplasia, benign tumors (ganglioglioma, ganglioneuroma, dysembryoplastic neuroepithelial tumor), and scars. Among the later, those originated after traumatic frontal depressed fractures are especially well suited for cortical resection (▶Fig. 10.2, ▶Fig. 10.3, ▶Fig. 10.4, ▶Fig. 10.5, ▶Fig. 10.6, ▶Fig. 10.7, ▶Fig. 10.8). ³

**Fig. 10.2** Cortical dysplasia as seen on MRI in patients with frontal lobe refractory epilepsy.

**Fig. 10.3** Above left: MRI showing right mesial frontal focal cortical dysplasia in a patient with frontal lobe epilepsy. Above right: Cortical resection is usually larger than the lesion itself in patients with cortical dysplasia. Below: Surgical specimen.

**Fig. 10.4** Above left: Sagittal MRI slice showing extensive left frontal cortical dysplasia in a patient with refractory epilepsy. Above right: Axial MRI slices for the same patient. Below left: Intraoperative picture showing the interictal (*white tags*) and ictal (*letter*) areas as defined by invasive recordings. Below right: Surgical specimen showing abnormal cortex invading the white matter.

**Fig. 10.5** Above left: Axial MRI scan showing a left frontal ganglioneuroma in a patient with epilepsy. Above right: Coronal MRI slice for this patient. Below left: Sagittal MRI showing resection of the lesion and perilesional cortex. Below right: Axial MRI slice showing the resected area.

**Fig. 10.6** Above left: Axial CT scan showing right frontal ganglioglioma associated with an arachnoid cyst. Above right: Axial MRI slice for this patient. Below left: Intraoperative picture showing the associated arachnoid cyst. Below right: Surgical specimen showing complete lesion removal.

**Fig. 10.7** Left: Preoperative axial MRI showing right frontal lobe scar derived from a traumatic depressed skull fracture. Right: Axial MRI slice showing the extent of sacrectomy.

**Fig. 10.8** Above left: Sagittal MRI slice showing left supplementary motor area (SMA) dysembryoplastic neuroepithelial tumor. Above middle: Intraoperative picture showing the mapped motor strip (*letters*), and the interictal activity (*white tags*) as seen over the convexity. Above right: Intraoperative picture showing complete removal of the left SMA. Below left: Postoperative axial MRI slice showing complete removal of the lesion. Below right: Postoperative coronal slice for this patient.

We have seen a decrease in the use of intraoperative electrocorticography (ECoG), awake craniotomy, and Wada test over the years. Whenever needed, electrophysiological data are obtained through prolonged (several days) continuous invasive recording sessions, turning intraoperative ECoG less relevant. Data previously obtained during awake craniotomy could be obtained in patients under general anesthesia (as is the case for motor strip mapping) or by bedside stimulation during invasive investigation. In most patients with normal MRI, the first noninvasive video-EEG session is a first step to guide a second video-EEG invasive recording.

Different imaging techniques have been used in the presurgical workup of patients with frontal lobe seizures and epilepsy. Interictal SPECT alone is not relevant; it must be combined with ictal SPECT and coregistered to MRI. ⁴ Even though, useful findings might be present in a small subgroup of patients with more prolonged seizures (longer than 60 seconds) or focal status. Most of the frontal lobe seizures are brief and not adequately detected by ictal SPECT. PET studies showed variable and inconsistent usefulness in frontal lobe epilepsy. ⁵ , ⁶ It is an interictal study which unlikely forward additional information in patients with normal MRI. MEG had shown some promising results in small series, but larger prospective studies are lacking. ⁷ , ⁸