Poor localization of the interictal epileptic abnormality and the rather unreliable EEG localization of ictal onsets in patients with frontal lobe epilepsy may be due to some of the following factors: (1) high risk of EEG sampling error, (2) early seizure spread within and outside the frontal lobe, (3) widespread distribution of the epileptogenic brain tissue responsible for the patient's habitual seizures, and (4) secondary bilateral synchrony and secondary epileptogenesis. The relevance of these factors in the preoperative investigation of patients with frontal lobe epilepsy was studied in: (a) 34 adult patients (mean age: 25 years) who became and persisted seizure free after restrictive surgical removal of the anterofrontal region, the parasagittal region convexity or the fronto-opercular area; (b) 12 patients in whom the pre-operative EEG investigation with extracranial electrodes failed to localize the site of seizure onset, leading to further investigation with depth electrodes.

The ictal clinical manifestations of 40 patients with frontal lobe epilepsy who became and remained seizure free after selective removal of the parasagittal or anterolaterodorsal convexities were studied. Seizures arising from the parasagittal region were characterized by a high incidence of somatosensory auras (60%) and by tonic and/or clonic motor behavior (100%) and never exhibited automatisms. Conversely, the anterolaterodorsal convexity group never showed somatosensory auras but often had warnings more typical of temporal lobe seizures, only displayed partial motor seizure activity in half the cases, and included a relatively high incidence of automatisms (30%). These clinical differences may be useful in the localization of frontal lobe epileptogenic foci. The manifestations of anterolaterodorsal convexity seizures may reflect frequent spread to the temporal lobe, whereas parasagittal convexity seizures often show initial ictal behavior, in keeping with seizure activity in that region. Early ictal unilateral head turning without other motor manifestations was seen in 3 of 10 patients in the parasagittal convexity group and in 9 of 30 patients in the anterolaterodorsal convexity group. In 11 of these 12 cases, the head turning was contralateral to the surgical removal.

.Surgical treatment for frontal lobe epilepsy provides both a challenge in localization and an opportunity to better understand the pathophysiology of this condition. EEG localization is difficult because anatomic and pathophysiologic characteristics of the frontal lobe result in widespread and generalized epileptiform activity at the scalp, generated from more focal epileptogenic zones. Preoperative EEG investigation of 34 adults and 45 children, who had surgical removal of frontal lobe epileptogenic zones, reveals a continuum of interictal disturbances, ranging from focal abnormalities to lobar and multilobar epileptogene sis. The degree and direction of spread of epileptogenic activity varies widely with the location of the source and with the age of the patient. Correlation of EEG data with ancillary diagnostic procedures is crucial for proper interpretation.