Resident of Neurology Univesity of Texas Health Science Center at Houston Houston, Texas
Rationale: Polymicogyria (PMG) comprises 20% of malformations of cortical development and occurs secondary to abnormal post-migrational development. Epilepsy, the most common clinical manifestation of PMG, presents in up to 85% of cases. However, up to 77% of patients progress to become refractory to antiepileptic drugs (AED). Diagnosis of PMG is mainly by MRI where a distinct stippled gray-white junction and normal to increased cortical thickness is noted. Methods: We retrospectively identified patients with refractory epilepsy and PMG, who had undergone surgical intervention in our center, January 2012 to February 2020. PMG was diagnosed by MRI or pathology reports. Medical records of patients were abstracted for age at onset of epilepsy, age at surgery, AEDs, and epileptogenic zone (EZ) on long-term scalp video EEG monitoring. Invasive stereotactic EEG(SEEG) recordings were carefully studied. Seizure onset patterns were classified according to the classification by Montreal Neurological institute. Location of surgical intervention in regards to PMG abnormality was delineated. Patients were followed six weeks, six months and then yearly after surgical intervention. Outcome measures were defined by ILAE and Engel’s classifications. Results: Ten patients, six women and four men, with refractory epilepsy and PMG were included in this study. Age at onset of epilepsy ranged between six and 39 years, and age at operation between 15 and 60 years. Median number of failed AEDs was three. Sixty percent of patients had bilateral PMG. Six patients MRI showed other developmental cortical abnormalities than PMG, the most common being heterotopias, while in only 4 patients PMG was the sole abnormality. All except one patient underwent long term SEEG monitoring. Four seizure onset patterns were observed in intracranial EEG recording: clearly visible low voltage fast activity, spike and wave activity, a single burst of high amplitude polyspikes, 0.5-2 Hz high voltage spiking. EZ involved the PMG in 8 and was remote from it in one patient. Surgical intervention consisted of resection of all or part of the PMG in 4 patents, and laser interstitial thermal therapy (LITT) of PMG ± PVNH in four. Two patients were treated by a combination of resection and LITT, in one of these patients the EZ did not include PMG and patient has been seizure free for 6 years. Four patients had achieved > 12 month seizure freedom in their last visit (ILAE class 1 and Engel class 1a), and two other had worthwhile reduction in seizure frequency. Three other patients were operated between six and 11 months prior to their last follow up, all seizure free. Conclusions: We report 90% favorable outcome rate in our study, thus confirming that epilepsy surgery in the PMG population is worthwhile pursuing. Our findings indicate that the EZ is often smaller than the extent of PMG and sometimes remote from it, and thus intracranial EEG is a valuable tool in delineating the EZ. In contrast to studies that have reported good outcomes after hemispherectomy and gross total resection of PMG, we demonstrate that LITT and limited, tailored resections smaller than the extent of PMG, still prove to have favorable epilepsy outcomes. Funding: Please list any funding that was received in support of this abstract.: No funds
