(265) Corpus Callosotomy and Intracranial Electroencephalogram: Multi-Staged Diagnostic Procedure for Epileptogenic Focus Lateralization and Localization in Medically Refractory Focal Epilepsy Syndrome for Epilepsy Surgery

Rationale: Corpus callosotomy (CC) is a palliative procedure where white-matter tracts of the anterior two-third or entire corpus callosum are severed as a treatment for medically refractory generalized epilepsy syndromes. While CC does not lead to seizure-freedom, the aim is reducing seizure severity by interrupting generalization. CC is effective in generalized epilepsy and epileptic encephalopathies, with no therapeutic role in focal epilepsy syndromes. Recently, CC has emerged with diagnostic value with only a few reports discussing the use of bilateral intracranial electroencephalogram (iEEG) prior to and post-CC as a multi-staged procedure for epileptogenic focus localization. We present a patient with focal epilepsy syndrome with secondary generalization where CC, as part of a multi-staged procedure, was utilized for the initial lateralization of the epileptogenic focus prior to iEEG.

Methods: We reviewed clinical, radiographic, and EEG reports of our patient. We searched PubMed for literature using terms “corpus callosotomy & focal epilepsy” and “corpus callosotomy & focal epilepsy & intracranial EEG.”

Results: Twenty-three-year-old right-handed man with medically refractory focal epilepsy syndrome with secondary generalization since age of six presented to our institute for evaluation. Seizure frequency gradually worsened from two to three to six to seven events per day, primarily during sleep and triggered by sleep deprivation. Seizure semiology was characterized by eyes rolled back, head drops, grunting noise, head turning to the left, raising of bilateral arms with tonic-clonic activity, < 1-minute duration, followed by return to his baseline. He was on phenobarbital, but then developed Stevens-Johnson syndrome. Lamotrigine was avoided. Phenytoin, oxcarbazepine, levetiracetam, and lacosamide were ineffective. He was maintained on divalproex sodium, topiramate, and clorazepate. Vagus nerve stimulation therapy was refused. Routine EEG and magnetic resonance imaging of the brain were unremarkable. Initial video-EEG revealed several typical seizure events. Electrographic correlate showed slowing over the F3 and C3 regions with rapid generalization and significant myogenic artifact, making it difficult to lateralize/localize the epileptogenic focus. Ictal single-photon emission computed tomography (SPECT) revealed hyperperfusion in the right anterolateral temporal lobe. He then underwent anterior CC, but continued having seizures at the same frequency, but of shorter duration and changed semiology, characterized by left arm numbness and tonic-clonic activity. Repeat video-EEG status post anterior CC showed six right hemispheric seizures, maximal at P4, F8, C4 regions, with interictal right frontal-central-parietal sharp-wave complexes. Given seizure frequency, he was referred for phase 2 iEEG for epileptogenic focus localization prior to epilepsy surgery.

Searching terms “corpus callosotomy & focal epilepsy” on PubMed yielded 152 results, while “corpus callosotomy & focal epilepsy & intracranial EEG” yielded 26 results, of which, only three were relevant to the topic.

Conclusions: CC is a palliative procedure for medically refractory generalized epilepsy syndromes. While CC has no therapeutic benefit in focal epilepsy syndromes, it has emerged with diagnostic value. Only a few studies have discussed the role of CC and iEEG, as a multi-staged diagnostic procedure for the lateralization and localization of an epileptogenic focus prior to epilepsy surgery. While Phase 2 iEEG is standard of care for identifying epilepsy surgery candidates, CC as a staged procedure has diagnostic value in the initial lateralization of the epileptogenic focus in focal epilepsy syndromes with secondary generalization.   

Funding: Please list any funding that was received in support of this abstract.: None