Introduction: Corpus callosotomy is a palliative procedure for the treatment of epilepsy which is particularly effective for drop attacks and generalized seizures[1,2]. Seizure lateralization after callosotomy has also been described[3,4]. Callosotomies have been successfully performed using traditional, endoscopic, CO2-laser, and radiosurgical approaches[5,6,7]. Magnetic resonance imaging (MRI)-guided laser interstitial thermal therapy (LITT) is a minimally invasive procedure that is gaining increasing use to treat a variety of brain abnormalities associated with tumor and epilepsy. Here we report corpus callosotomy performed in four patients using LITT.
Methods: Retrospective chart and magnetic resonance imaging (MRI) review was performed on all cases undergoing LITT callosotomy at one center. Seizure outcomes were followed for 18 months. Diffusion tensor imaging (DTI), resting functional magnetic resonance imaging (rfMRI) and electrophysiological connectivity analysis including corticocortical evoked potential (CCEP) and resting electrocorticogram (ECoG) were performed.
Results: Three patients underwent intracranial SEEG depth electrode recording prior to surgical intervention revealing bilaterally synchronous seizure onsets; scalp EEG demonstrated rapid bisynchronous secondary generalization in the fourth patient. These four patients elected for MRI-guided LITT ablation of the anterior corpus callosum which was successfully completed as a single procedure in three patients. Due to a misplaced device, one patient required a second LITT procedure. The extent of the callosotomy was confirmed using diffusion tensor imaging (DTI). Functional separation of the hemispheres was characterized using resting state function magnetic resonance imaging (rs-fMRI), cortico-cortical evoked potentials and resting electrocorticographic connectivity. Post-callosotomy SEEG monitoring revealed seizure lateralization in 3 of the electrode implanted patients. Two patients undergoing subsequent focal resection are seizure free at 18 months. The remaining patients experienced an 83% and 100% decrease in generalized seizure frequency following callosotomy. No patients suffered neurological morbidity, including disconnection syndromes.
Conclusions: MRI-guided LITT provides a viable minimally-invasive alternative approach to corpus callosotomy in the treatment of medically intractable epilepsy.
Patient Care: Here, for the first time, we demonstrate the use of laser-interstitial thermal therapy (LITT) for corpus callosotomy in a series of patients with medically intractable epilepsy. LITT is gaining increasing use for the treatment of neoplasms, radiation necrosis, and epileptic foci, but has not been previously shown to be useful for functional disconnection via anterior callosotomy. Many patients with epilepsy are hesitant to undergo open craniotomies, and LITT-mediated callosotomy is a viable alternative to traditional procedures. LITT offers numerous advantages to previous methods including a less invasive approach to the corpus callosum obviating the need for craniotomy and concomitant surgical approach risk and real-time monitoring of lesioning via MRI-based thermometry. The extent of the callosotomies performed in this study was confirmed anatomically with post contrast MRI and diffusion tensor imaging. Functional disconnection of the cerebral hemispheres was demonstrated with interictal and ictal intracranial electroencephalography, functional MRI, functional electrocorticography, and cortico-cortical evoked potentials, providing evidence that callosal fibers are effectively disrupted by LITT and demonstrating the utility of these investigations in predicting the outcome of epilepsy surgery.
Learning Objectives: By the conclusion of this session, participants should be able to:
1. Describe the indications for corpus callosotomy in the treatment of medically retractable epilepsy.
2. Discuss the advantages and disadvantages of laser interstitial thermal therapy for callosotomy compared to traditional callosotomy.
3. Describe the roles of modern neuroimaging (DTI, fMRI) and electrophysiology (eCoG, SEEG, CCEP) in assessing the functional outcome of corpus callosotomy and other neurosurgical procedures.
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