The purpose of this study was to investigate the cortical reorganization associated with congenital brain lesion such as intracerebral arteriovenous malformation (AVM). Dipole source localization of somatosensory evoked potential (SEP) was performed in five patients with AVM encompassing sensorimotor cortex. Dipole tracing method combined with the scalp-skull-brain head model (Homma et al., 1994) was used to locate dipole source of an early cortical component of SEP elicited by median nerve electrical stimulation. The location of dipole source of SEP, which could be considered as the hand area of primary somatosensory area, was shown in the realistic section of the head and could be easily superimposed on the magnetic resonance imaging. SEP was recorded three times in each patients and the results were reproducible. In 2 patients whose postcentral gyrus was not involved in AVM, the dipole source of SEP was localized in the intact postcentral gyrus. The locations of dipole sources of SEP in the both hemisphere were symmetrical. In 3 patients whose postcentral gyrus was encompassed by AVM, the dipole source of SEP was localized in the surrounding intact gyrus which was distant from the usual region of postcentral gyrus. Somatotopy was different from the normal pattern. The hand area was located more medially than usual observed in normal postcentral gyrus. Despite the paucity of the number of patients and data obtained by dipole source localization, our findings support the existence of reorganization in the cerebral cortex with congenital lesion such as AVM. These findings of aberrant mapping of cortical function may be explained by the plasticity of brain function. The developing brain can inherit function that would normally have been performed by the region of brain involved in the lesion. We demonstrated that dipole tracing of SEP was a noninvasive method used to localize areas of eloquent cortex in patients harboring AVM. This method is of value in treatment planning.
Adolescent Adult