Subcortical nodular heterotopia: a functional MRI and somatosensory evoked potentials study

Subcortical nodular heterotopia (SNH) associated with refractory epilepsy may be surgically treated, and a positive outcome can be expected following the complete excision of the malformed tissue. Recent functional neuroimaging studies have suggested the possible functional relevance of cerebral malformations, and may make it possible to improve presurgical planning, thus allowing extended resections and minimising post-operative deficits. We here report the case of a 19-year-old man with epilepsy and a giant SNH associated with diffused abnormal gyrations of the right temporal-parietal regions. Cortical functional organisation was investigated by means of functional magnetic resonance imaging (MRI) during sensory and motor tasks, and somatosensory evoked potentials. The results revealed enlarged and displaced motor and sensory cortical areas with heterotopic tissue functional activation. The relevance of these findings is discussed in the light of the possible surgical treatment of drug-refractory epilepsy associated with cerebral malformations: surgical treatment based on conventional MRI studies alone, without taking the functional nature of dysplastic tissues into account, may lead to considerable side effects.