Leaving tissue associated with infrequent intracranial EEG seizure onsets is compatible with post-operative seizure freedom

Abstract

Identify seizure onset electrodes that need to be resected for seizure freedom in children undergoing intracranial electroencephalography recording for treatment of medically refractory epilepsy. All children undergoing intracranial electroencephalography subdural grid electrode placement at the Children's Hospital of Philadelphia from 2002-2008 were asked to enroll. We utilized intraoperative pictures to determine the location of the electrodes and define the resection cavity. A total of 15 patients had surgical fields that allowed for complete identification of the electrodes over the area of resection. Eight of 15 patients were seizure free after a follow up of 1.7 to 8 yr. Only one seizure-free patient had complete resection of all seizure onset associated tissue. Seizure free patients had resection of 64.1% of the seizure onset electrode associated tissue, compared to 35.2% in the not seizure free patients (p=0.05). Resection of tissue associated with infrequent seizure onsets did not appear to be important for seizure freedom. Resecting ≥ 90% of the electrodes from the predominant seizure contacts predicted post-operative seizure freedom (p=0.007). The best predictor of seizure freedom was resecting ≥ 90% of tissue involved in majority of a patient's seizures. Resection of tissue under infrequent seizure onset electrodes was not necessary for seizure freedom.

Keywords: Epilepsy; cortical dysplasia; epilepsy surgery; intracranial electroencephalography; neocortical epilepsy.

Fig 1

(A) Pre-resection picture taken in the operating room with electrodes on the surface of the brain. (B) Picture taken in the operating room post-resection. Black line is our approximation of the resection cavity.

Fig. 2

Graphs from the seizure free patients showing number of seizure onsets on the Y-axis arising from each electrode on the X-axis. The color of each bar represents if the tissue underlying the electrode was resected. Red-resected; yellow-the edge of the resection was immediately under the electrode; blue-unresected. Patient 7 is the only patient with a complete resection of all the seizure onset electrode associated tissue. Patients 1,2,3,4 and 6 had ≥ 90% of the associated tissue resected from the most common seizure onset electrodes. Patients 5 and especially patient 8 had < 90% of the associated tissue resected from the most common seizure onset electrodes but was still seizure free.

Fig. 3

Graphs from the non-seizure free patients showing number of seizure onsets on the Y-axis arising from each electrode on the X-axis. The color of each bar represents if the tissue underlying the electrode was resected. Red-resected; yellow-the edge of the resection was immediately under the electrode; Blue-unresected. While several patients had tissue resected that was associated with a large number of seizure onset electrodes, see 12 and 14. None of the patients had ≥ 90% of the tissue associated with the most frequent seizure onset electrodes.