Abstracts

Rationale: Periventricular nodular heterotopia (PVNH) is a malformation of cortical development frequently associated with intractable epilepsy. Categorical involvement of the nodular tissue in normal functions and in epileptogenesis of overlying cortex and mesial temporal structures is unclear. Evidence suggests that PVNH is not only associated with epileptic activity through abnormal connectivity, but may itself possess physiological cerebral functions. Surgical treatment may thus pose a challenge and a risk for functional deficit following resective or ablative therapies. Methods: We performed a retrospective review and identified four patients with medically refractory epilepsy and PVNH who underwent a comprehensive epilepsy surgical evaluation, including intracranial stereo-EEG monitoring (SEEG) and extraoperative functional mapping of the sampled heterotopic nodules, overlying cortex and/or mesial temporal structures. Results: Stimulation of heterotopic tissue produced visual symptoms, including visual scotoma, visual oscillations, and teleopsia/pelopsia. In one patient, in whom ictal onset occurred independently in the left and right hippocampi but not in either of the bilateral PVNH, these symptoms represented his typical seizure aura in the absence of afterdischarges or electrographic seizures. Conclusions: We demonstrate that heterotopic tissue in PVNH has physiologic cerebral functions, irrespective of its role in epileptogenesis. SEEG affords opportunities for in-depth evaluation of epileptic and functional networks that may be especially important in the setting of PVNH. Our findings inform clinical practice, including surgical management and decision making, as well as patient counselling with respect to the rationale for diagnostic testing and surgical options and risks. Funding: None