Frontal Lobe Epilepsy Surgery — The Importance of Patient Selection
Abstract & Commentary
By Theodore H. Schwartz, MD, FACS, Associate Professor of Neurosurgery, Neurology and Neuroscience, Weill Cornell Medical College, NewYork Presbyterian Hospital. Dr. Schwartz reports no financial relationship relevant to this field of study.
Synopsis: Surgery for frontal lobe epilepsy can be very effective in patients with a localized ictal onset zone, focal MRI abnormalities, nocturnal epilepsy and complete resection of the epileptic zone and/or imaging abnormality.
Sources: Jeha LE et. al. Surgical outcome and prognostic factors of frontal lobe epilepsy surgery. Brain. 2007;130:574-584. Nobili L, et. al. Surgical treatment of drug-resistant nocturnal frontal lobe epilepsy. Brain. 2007;130:561-573.
As opposed to temporal lobe epilepsy, which has a well-documented 70%-80% rate of seizure-freedom following surgery in well-selected cases, frontal lobe epilepsy surgery is more controversial. Published reports indicate that anywhere from 13%-80% of patients are seizure-free after surgery. Many of these reports are from the pre-MRI era and lump together patients with lesional and non-lesional epilepsy. Hence, there is little data on predictors of successful frontal lobe epilepsy.
Two recent articles in Brain address the question of outcome following frontal lobe epilepsy surgery. From the Cleveland Clinic, Jeha et al present 70 patients who underwent frontal lobe resections for intractable epilepsy. Overall, seizure-free rates started at 56% at one-year but decreased to 30% after 5 years. However, the authors were able to identify the most important factors that predicted a favorable outcome. Patients with MRI abnormalities limited to the frontal lobe, absence of generalized ictal EEG patterns, absence of early post-operative seizures and complete resection of the epileptic focus or imaging abnormality were more likely to be seizure-free after surgery. Patients with any one of these predictors had a 40% seizure-free rate at 5 years. Patients with all the indicators had an 85% chance of being seizure-free.
Nobili et al report from Milan on 21 patients with nocturnal frontal lobe epilepsy (NFLE). Patients with NFLE present with seizures that occur almost exclusively during sleep. Although NFLE is thought to be a benign medication-responsive type of epilepsy, ~30% of patients are resistant to medical treatment and suffer from, not only frequent seizures, but also excessive daytime sleepiness. Although half of the patients in this study had normal MRI scans, following surgery 76% were seizure-free after a mean follow-up of 42 months and 100% were improved (Engel I-III). Remarkably, all patients with excessive daytime sleepiness were relieved of this symptom, even if they were not cured of their seizures. The authors attribute their success to the high rate of patients with Taylor-type focal cortical dysplasia. Morbidity was quite low with only transient motor signs related to the proximity of the resections to the supplementary motor area.
Commentary
Unlike the temporal lobe, the frontal lobe is a large region of relatively homogeneous-looking brain. The medial surface lies along the falx and the inferior surface along the base of the anterior fossa, both areas difficult to expose with a standard craniotomy. MR imaging in patients with frontal lobe epilepsy often reveals no obvious abnormality. Consequently, identification and adequate resection of topographically large and complex frontal lobe epileptogenic regions can be quite difficult. Migration abnormalities, which may involve widespread areas of brain, are common in the frontal lobe and the semiology of the seizures is often ambiguous. For this reason, some epileptologists are reluctant to pursue an aggressive surgical approach in patients with suspected frontal lobe epilepsy for fear that the risks of surgery may outweigh the perceived low therapeutic yield.
Both articles presented in this paper indicate that frontal lobe epilepsy surgery can be extremely successful and even approach the success rates for temporal lobe surgery. Not surprisingly, the more focal the EEG and imaging abnormalities, the more successful the surgery. The authors imply that with appropriate patient selection at a high volume center, following aggressive work-up (>75% of the patients required invasive subdural electrode monitoring), the outcome will be favorable enough to outweigh the risks. However, several questions remain unanswered. First, neither author actually presents the surgical risks in any detailed fashion. Jeha et al don't even mention any risks or adverse outcomes from surgery. Perhaps the authors felt that surgical risks were not the focus of the paper, yet these must be weighed closely against the chance of attaining seizure-freedom and are critical to the decision-making process. Second, it has been well-understood for years that the more focal the epileptogenic region, the more successful the surgery. For decades, papers have argued that epilepsy surgery should be performed at high volume centers to increase its efficacy since patient selection is so critical. Nevertheless, at the Cleveland Clinic, 25% of the patients with frontal lobe epilepsy who were selected for surgical resection had multifocal ictal onsets. Either the intent was palliative, in which case they should not be included in this paper on cure rates, or physicians at tertiary care epilepsy centers feel obliged to offer aggressive therapy even in cases with a low chance of cure. Once a patient is implanted with electrodes, it is difficult to remove them without offering a surgical resection that might improve their outcome, even if the chance of enduring cure is low. Hopefully, we can use the data from these articles to eliminate patients from consideration for surgery if their outcome will not likely be favorable. On the other hand, even a 15% cure-rate might be worth the risk in very severe cases.
Finally, it is most interesting to note that patients with NFLE and excessive daytime sleepiness observed resolution of this symptom after frontal lobe surgery, even if their seizures were only improved but not cured. It has long been a dictum in epilepsy surgery that patients' quality of life does not improve unless they are completely seizure-free. Hopefully the authors will measure quality of life using a validated questionnaire in this group of patients to confirm this finding.
Surgery for frontal lobe epilepsy can be very effective in patients with a localized ictal onset zone, focal MRI abnormalities, nocturnal epilepsy and complete resection of the epileptic zone and/or imaging abnormality.You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
- Award-winning Medical Content
- Latest Advances & Development in Medicine
- Unbiased Content