Abstracts

Rationale: Stereotactic laser amygdalo-hippocampotomy (SLAH) through magnetic resonance imaging-guided laser interstitial thermal therapy (MRIgLITT) represents a minimally invasive treatment option for patients experiencing medically intractable mesial temporal lobe epilepsy (MTLE).  Although more widely applicable in the adult population due to a higher prevalence of MTLE, SLAH offers potential benefit in carefully selected pediatric patients with MTLE as well.  Multiple publications have described the utility and operative techniques of SLAH, assuming standard neuroanatomy and typical findings of mesial temporal sclerosis (MTS).  However, no articles address the technical challenges and nuances with  performing SLAH in patients with variant anatomy.  Specifically, stereotactic laser ablation (SLA) of mesial temporal structures in the context of ventriculomegaly and aberrant hippocampal anatomy has not been reported.  This effort presents operative techniques and nuances of SLAH in the setting of ventriculomegaly and variant hippocampal anatomy. Methods: The operative approaches and peri-operative imaging for pediatric patients with medically intractable MTLE undergoing SLAH at the authors' institution were retrospectively reviewed.  Patients with normal ventricular size and standard hippocampal configuration (despite abnormal internal architecture and the presencence of MTS) were differentiated from a patient with ventriculomegaly and abnormal medial displacement of the hippocampal head.  Individuals from the epilepsy surgery team (neurosurgery, neurology, and neuroradiology) compared pre-operative imaging sequences in the patients with and without ventriculomegaly to develop an appropriate surgical approach and trajectory for SLA of the mesial temporal structures in the setting of ventriculomegaly and variant hippocampal anatomic configuration. Results: A modified surgical approach and trajectory of SLA was developed and performed in the setting of ventriculomegaly and variant hippocampal anatomic configuration.  The modified trajectory fulfilled the following criteria:  avoiding ependymal surfaces and ventricular entry; entering the hippocampus at the anterior-posterior level of the lateral mesencephalic sulcus; and maintaining centralized location through the hippocampal body and head.  The technical variations of this procedure included a more infero-laterally displaced entry site and a more medialized trajectory than standard approaches for SLAH.  Additionally, the presence of ventriculomegaly and medial displacement of the hippocampal head precluded SLA of the amygdala in this context.  Real time thermography, estimated treatment zones of MRIgLITT, and post-ablation imaging demonstrated thorough ablation of the hippocampal head, body, and body-tail junction with preservation of adjacent neurovascular structures. Conclusions: SLA through MRIgLITT remains a safe and viable treatment option for medically intractable MTLE in patients with ventriculomegaly and variant hippocampal anatomic configuration.  A modified approach with infero-lateral displacement of the entry site and medialization of the standard trajectory may be required to avoid ependymal surfaces and ventricular entry while accomplishing hippocampal entry at the anterior-posterior level of the lateral mesencephalic sulcus.  Ventricular enlargement and medial displacement of the hippocampal head may preclude inclusion of the amygdala, resulting in SLH as opposed to SLAH.  The clinical significance of excluding the amygdala from SLA in this context is not known. Funding: None.