Abstracts

Surgical selection is evolving to a point in which localization of the epileptogenic zone and eloquent functional cortex prior to any surgery is vital. In patients with intractable epilepsy associated with malformations of cortical development (MCD) in the rolandic regions, the pre-surgical evaluation is a challenge because unpredictable localization of the primary somatosensory function may exist. This localization is essential for optimal patient selection and surgical strategy. Experiments in animals and observations in humans indicate that the cerebral cortex has the capability to adapt to injury through a range of different mechanisms of changes including functional reorganization of intact cortical areas. Evidence of brain reorganization has been observed in patients who have suffered strokes, limb amputation, and brain injury early in life. The main question to be answered is whether functional reorganization of somatosensory cortex exists in MCD involving these cortical regions. This information was obtained by means of magnetoencephalography (MEG).
Consecutive patients presented with medically intractable epilepsy and MCD in the rolandic regions were selected based on MRI findings. The patients underwent routine pre-surgical evaluation including intracranial EEG evaluation. Identified patients had a 148-channel whole head MEG study to identified the localization of the somatosensory cortices. A validated localization of the sensory cortical function that is more than 2.0 cm distant (center-to-center) from expected anatomic localization (based on intrasubject control mapping in the contralateral non-lesional hemisphere) was considered representative of reorganized function. Additionally, disturbance of homuncular arrangement as compared to that expected upon general anatomic rules and confirmed against the unaffected contralateral side was considered as reorganized function.
Seven patients (n=7) were included in the study. Four patients had focal cortical dysplasia, two polymicrogyria and schizencephaly, and one had isolated polymicrogiria involving the rolandic areas. In the four patients with cortical dysplasias, the somatosensory cortices were identified outside the rolandic area, and were considered to be reorganized. In the two patients with polymicrogyria and schizencephaly the somatosensory cortices remained in the rolandic areas if the anatomy was not distorted by the presence of the schizencephalic cleft, revealing no reorganization. In the patient with isolated polymicrogyria the somatosensory cortex remained in the rolandic area.
In patients with epileptic MCDs involving the rolandic areas, the somatosensory cortices may be reorganized if the MCDs are due to an abnormal neuronal and/or glial proliferation (i.e. cortical dysplasia with balloon cells), but may not in MCD due to abnormal cortical organization (i.e. polymicrigyria)
[Supported by: An educational grant from the Epilepsy Foundation of America (JGB).]