Timing and type of congenital brain lesion determine different patterns of language lateralization in hemiplegic children.

Cerebral lateralization for language has been assessed by means of the Fused Dichotic Words Test in 26 hemiplegic children (mean age 7 years 2 months) with congenital focal brain damage (ten with left, seven with right and nine with bilateral lesions). The specific aim of the study was to investigate the relation between lesion characteristics (side, size and localization) at high field, multiple plane MRI and the pattern of language lateralization at the dichotic test. Significant side and site effects were found at group level; in children with lesions of the left hemisphere a left ear advantage (LEA) was found, while children with right lesions had the expected right ear advantage (REA). Analysis of individual data, however, revealed that type of lesion, cortical-subcortical or periventricular, occurring at term or preterm age, respectively, may be the primary factor responsible for inter versus intrahemispheric organization of language after congenital brain lesions. Only when the left lesions involved cortical-subcortical regions encroaching the temporal lobe and occurred at term age, was language reorganized in the right hemisphere; when lesions (whether left or right) involved only the periventricular white matter and occurred at preterm age, language was lateralized in the left hemisphere. Our results provide evidence that within 'congenital hemiplegias', strictly defined as hemiplegias whose causal lesion occurs before the end of the neonatal period, different recovery mechanisms are at work, depending on the type of brain lesion (neuropathology) which largely depends on the timing of insult (preterm vs. term period).