A MAGNETIC-RESONANCE-IMAGING STUDY OF PLANUM TEMPORALE ASYMMETRY IN MEN WITH DEVELOPMENTAL DYSLEXIA

Background: Imaging studies have suggested anomalous anatomical asymme tries in language-related regions of the temporal and parietal lobes i n individuals with developmental dyslexia. Autopsy studies have report ed unusual symmetry of the planum temporale (PT) in patients with dysl exia. Methodological limitations characterize much of this literature, however. Objective: To examine the size and asymmetry of the PT and i ts extension into the parietal lobe (planum parietale [PP]) in men wit h well-characterized, persistent dyslexia by using magnetic resonance imaging and 3-dimensional surface rendering techniques. Methods: The b rains of 16 right-handed dyslexic men aged 18 to 40)rears and 14 match ed control subjects were studied with magnetic resonance imaging. Most of these subjects were previously studied with positron emission tomo graphy, which demonstrated functional abnormalities in temporal and pa rietal brain regions in the dyslexic group. The area of the PT was det ermined with the aid of 3-dimensional surface-rendering techniques. Th e size of the PP was estimated by measuring the length of the posterio r ascending ramus on 3 parasagittal slices. Results: Approximately 70% to 80% of both groups showed equivalent leftward (left>right) asymmet ries of the PT; approximately 50% to 60% showed equivalent rightward ( right>left) asymmetries of the PP. These asymmetries showed equivalent moderate inverse correlations with each other in both groups. Conclus ions: These results challenge the notion that anomalous asymmetry of t he PT is strongly associated with developmental dyslexia. Given the he terogeneity of the dyslexic population, some subgroup of dyslexic indi viduals tie, those with developmental language disorders) may show unu sual symmetry or reversed asymmetry in this region. However, anomalous asymmetry of the planum did not contribute to functional abnormalitie s demonstrated in these patients by positron emission tomography.