Single-stage resection of bottom-of-a-sulcus dysplasia involving eloquent cortex using navigated transcranial magnetic stimulation and intraoperative modalities.

BACKGROUND: Focal cortical dysplasia (FCD) is a common etiology of refractory epilepsy, particularly in children. Surgical management is potentially curative, but poses the challenge of distinguishing the border between ictogenic regions of dysplasia and functionally critical brain tissue. Bottom-of-a-sulcus dysplasia (BOSD) amplifies this challenge, due to difficulties in physiologic mapping of the deep tissue.
METHODS: We report a one-stage resection of a dysplasia-associated seizure focus abutting and involving the hand and face primary motor cortex. In doing so, we describe our surgical planning integrating neuronavigated transcranial magnetic stimulation (nTMS) for functional motor mapping, combined with intraoperative ultrasonography, intracranial electroencephalography, and magnetic resonance imaging (MRI). A 5-year-old girl with intractable focal epilepsy was referred to our comprehensive epilepsy program. Despite attentive pharmacotherapy, she experienced status epilepticus and up to 70 seizures per day, accompanied by multiple side effects from her antiseizure medication. A right frontal BOSD in close proximity to the hand motor area of the precentral gyrus was identified on MRI. Postoperatively, she is seizure-free for over 1 year with no hand deficit.
CONCLUSION: Although technically complex, single-stage resection taking advantage of comprehensive surgical planning with optimized fusion of functional mapping and intraoperative modalities merits consideration given the invasiveness of a two-stage approach for limited added value. Integrated pre-surgical nTMS allowed for mapping of eloquent cortex without invasive electrocortical stimulation.