Language hemispheric dominance in patients with congenital lesions of eloquent brain

OBJECTIVE: In 90% of normal subjects, the left hemisphere is dominant for l anguage function. We investigated whether congenital lesions of the left pe risylvian regions altered cortical language representation in right-handed individuals. METHODS: Using functional magnetic resonance imaging, we studied language h emispheric dominance in five right-handed adult patients with congenitally acquired arteriovenous malformations (AVMs) originating from left hemispher ic cortical language regions. The AVMs had not caused neurological symptoms during early development, but patients presented as adults with migraine, seizure, or minor hemorrhage. Results obtained from the AVM patients were c ontrasted to those from right-handed brain-injured stroke patients recoveri ng from aphasia and to those from right-handed normal subjects. RESULTS: During silent picture naming and verb generation tasks, cortical l anguage networks lateralized primarily to the right hemisphere in the AVM g roup, compared with the left hemisphere in the normal group. This right hem isphere-shifted language network in the AVM group exceeded the shifts towar d right hemispheric dominance found in the stroke group. CONCLUSION: Patients with AVMs affecting the left perisylvian regions recru ited the right hemisphere into language processing networks during early de velopment, presumably in response to congenitally aberrant circulation. Thi s early right hemisphere recruitment in the AVM patients exceeded the simil ar process in the brains of stroke patients whose left cortical language ne tworks were damaged in adulthood. Our data provide evidence of effective pl asticity in the developing human brain compared with the mature brain respo nse to injury. Knowledge of cortical language representation should assist presurgical planning in patients with developmental anomalies affecting app arently language-dominant brain regions.