Focal Cortical Dysplasia: A Review of Pathological Features, Genetics, and Surgical Outcome

Vincent Y. Wang, M.D. Ph.D.; Edward F. Chang, M.D.; Nicholas M. Barbaro, M.D.

Disclosures

Neurosurg Focus. 2006;20(1) 

In This Article

Surgery for FCD

Since the report by Taylor, et al., in 1971,[50] FCD has become increasingly recognized as a cause of medically refractory epilepsy. With advances in neuroimaging and electrophysiological monitoring, lesions in FCD can be more accurately identified and are thus more amenable to resection.

Epilepsy remains the most common presentation of FCD. Approximately one half of patients with epilepsy have some form of FCD;[6] however, some patients with Type I FCD may not show symptoms or may show only mild cognitive impairment.

Medically refractory epilepsy is the main reason for surgical intervention in patients with FCD. Preoperative neuroimaging usually includes high-resolution MR imaging, which can reveal approximately 60 to 90% of cortical abnormalities in these patients.[4,6,10] Characteristic findings include an abnormal gyral pattern, increased cortical thickness, poor gray-white matter differentiation, and increased subcortical signal intensity on T2-weighted and fluid-attenuated inversion-recovery MR images.[4,6,11] Many patients, especially those with normal MR imaging findings, undergo additional diagnostic procedures. Scalp EEG is frequently used and was one of the more important modalities during early surgical series. Approximately one half to two thirds of patients with abnormal EEG findings have a regional ictal abnormality.[4,6] In some cases, intracranial subdural recordings, most commonly with grid arrays, are used. Chronic subdural recording allows identification of eloquent cortex, in addition to definition of the epileptogenic region.[6]

The first published description of a surgical series of patients with FCD was by Taylor, et al.,[50] in 1971. This seminal study included a total of 10 patients, eight of whom had FCD that was confirmed by histological findings. Six of these patients became seizure free after surgery.

The first large series was described by Palmini, et al.,[40] in 1991. This series included 26 patients with focal neuronal migration disorders, 12 of whom had definitive FCD. Five of the 12 patients had lesions confined to one lobe or one area of the brain, and seven had multilobar involvement. Seven of the 12 patients had complete cessation or excellent control of seizures after surgery.[39] Seizure control was highly correlated with successful resection of the entire lesion or at least the majority of the abnormal tissue. Complete resection did not necessarily predict cessation of seizures, however, as poor control of seizures remained in some patients despite removal of all of the tissue associated with epileptiform discharges in EEG or electrocorticography findings. In 1995, Palmini, et al.,[41] further characterized these patients, as well as additional patients from two other institutions. In this series of 34 patients, outcome data were available for 27 patients. An important aspect of this study was the careful documentation of the EEG findings in patients with cortical dysplasia. Approximately two thirds of the patients demonstrated characteristic epileptic discharges, including repetitive electrographic seizure activity, repetitive bursting discharges, and continuous or quasicontinuous rhythmic spiking. In this expanded series with longer follow up, 75% of the patients who underwent complete resection of regions associated with abnormal electrical activities had a good outcome, and the patients in whom some of these areas remained had relatively poor seizure control. Thus, the concept of combined resection of areas showing radiological and electrophysiological abnormalities was emphasized.

Several reports on surgical series were published in the 1990s. Hirabayshi, et al.,[24] compared seizure control after surgery in patients with FCD and patients with mesial temporal sclerosis. Only six of 17 patients with FCD became seizure free or almost seizure free after the surgery, a significantly worse rate of seizure control, compared with the rate for patients who underwent surgery for mesial temporal sclerosis. Outcome was correlated with the extent of the pathological lesions. Involvement of tissue outside of the temporal or frontal lobes was an independent predictor of poor outcome, whereas frontal lesions and temporal locations were factors favoring a good surgical outcome. Otsubo, et al.,[38] reported on nine children with FCD who underwent resection between 1987 and 1991. Three patients became seizure free after the surgery. There was no conclusion about a relationship between the extent of resection and outcome.Wyllie, et al.,[52] reported results for 30 patients after surgery for migration disorders. Sixteen patients with extratemporal epilepsy were available for follow up, 13 of whom either became seizure free or had greater than 90% reduction of seizure frequency. In this study, 13 patients had Type I FCD involving the temporal lobe. None of them showed abnormalities on MR images. It is important to note that 10 of these patients became seizure free after surgery and the other three reported significant reductions in seizures. Kuzniecky, et al.,[30] described 11 patients who underwent resection for frontocentral malformations. In 10 of the 11 patients, MR images showed abnormalities. In a group of four patients with frontal involvement, one patient became seizure free and the other three had significant reductions in seizures. Three of the five patients with central lesions demonstrated improvement in seizures after surgery, and the remaining two did not have significant improvement. The authors emphasized that regions of dysplasia could contain normally functioning tissue, which would preclude aggressive resection without production of significant neurological deficits.

In the past few years, descriptions of several additional series of patients who underwent surgery for FCD have been published. It is important to note that many of these studies have had longer follow-up times and have included the use of more advanced imaging techniques, compared with earlier studies. Kloss, et al.,[28] have reported on a series of 68 pediatric patients with FCD. Long-term complete seizure control was achieved in approximately 50% of the patients, and another 20% of the patients had excellent seizure control. No significant difference in seizure control after surgery was found between the patients who had Type I FCD and those who had Type II FCD. Again, complete resection of the lesion was the most important factor for complete seizure control. Hong, et al.,[25] have described a series of patients with cortical dysplasia who underwent surgery; nine of these patients had FCD. Complete cessation of seizures was observed in seven of the nine patients after surgery.

Tassi, et al.,[47] have reported on a series of 52 patients with focal dysplasia who underwent surgery. In addition to MR imaging and scalp EEG, stereo-EEG was used in some patients to localize the lesions. Overall, 70% of the patients who underwent resection experienced excellent outcomes, with cessation of seizures or more than a 90% reduction in seizure frequency. One interesting observation in this series was that patients with Type II FCD fared better than patients with Type I FCD. Seventy-five percent of the patients with Type II FCD had complete cessation of seizures, compared with 62% of patients with Type IA FCD and 50% of patients with Type IB FCD.

Kral, et al.,[29] have described 53 patients in whom a diagnosis of FCD was made, 72% of whom had complete cessation of seizures after surgery and an additional 4% of whom had no more than two seizures per year after surgery. Identification of structural abnormalities on MR images was key to predicting seizure outcome. Multilobar involvement was identified as a predictor of poor outcome in this study. It is important to note that there was no difference in outcome between the patients with temporal as compared to extratemporal involvement in this series. This finding is probably partly due to the fact that most of the extratemporal involvement was in the frontal lobe.

Bautista, et al.,[4] have reviewed their experience with surgical treatment of FCD in adults. In this large series of 55 patients, 36 patients had temporal lesions, 19 had extratemporal lesions, and four had multilobar involvement. Most of the patients (87%) showed focal lesions on MR images, and approximately 60% showed additional pathological features such as central nervous system infection, hippocampal sclerosis, or low-grade tumor. Overall, 65% of these patients became seizure free, and 19% had significant improvement.

In contrast, in a series of 39 pediatric patients that has been described by Hader, et al.,[21] 72% of the patients had good seizure control, although there was no significant correlation between seizure control and imaging characteristics, histopathological findings, or location of the lesions. It is important to note that 16 patients had incomplete resection of the lesion and underwent multiple subpial resections. One half of these demonstrated good seizure control after the procedure. Thus, multiple subpial resections may offer additional benefit, especially for patients in whom the abnormal tissue cannot be resected due to functional considerations.

Cohen-Gadol, et al.,[10] have reported their experience with 22 patients with FCD. As in other series, complete resection with histopathological confirmation of a clean margin predicted good outcome. Ninety-two percent of patients who underwent complete resection became seizure free after the procedure, compared with only 43% of the patients who had margins still positive for FCD. Of the 22 patients, 20 patients harbored abnormalities identified on MR images. As in other series, the lesion areas with abnormal discharge often extended beyond the abnormal area identified on MR images. Fauser, et al.,[18] have correlated the control of seizures after resection with histopathological findings and have found that patients with Type I FCD fared better than those with Type II FCD. Sixty-three percent of patients with Type IA and 55% of those with Type IB were seizure free after surgery, compared with 43% of patients with Type IIA and 50% of those with Type IIB.

Chapman, et al.,[9] have described outcomes for 24 patients who had intractable seizures and normal MR imaging findings. In 42% of these patients, FCD was found. Overall, 80% of the patients had a significant reduction in the number of seizures after resection. This finding suggests that many patients with intractable seizures and normal MR imaging findings may have FCD and that resection should still be attempted in these patients, as good outcomes are frequently observed.

Hamiwka, et al.,[22] have reported results of a 10-year follow up of patients who had cortical malformations and underwent resection. Thirty-one of these patients had FCD. Only 32% of the patients remained seizure free over 10 years. Once again, the extent of resection was the most important factor in determining seizure control outcome.

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