Significance of planum temporale and planum parietale morphologic features in neurofibromatosis type 1

Background: Neurofibromatosis type 1 (NF-1) is associated with learning disabilities and cognitive impairment in childhood and adolescence. Individuals with NF-1 have a propensity for brain hyperintensities on T2-weighted magnetic resonance images, macrocephaly, and optic gliomas. Few clear relationships between these central nervous system abnormalities and cognitive function, however, have been found in this population. Objectives: To determine whether planum temporale (PT) and planum parietale (PP) morphologic features are associated with learning disabilities in NF-1. Patients and Methods: We measured and compared the surface area, gray matter volume, and asymmetry of the PT and PP on T1-weighted MRIs from 24 children and adolescents with NF-1 and an equal number of controls. Relationships between these measurements and cognitive and academic achievement scores were examined. Results: The left PT in boys with NF-1 was significantly smaller in both surface area and gray matter volume compared with girls with NF-1 and controls. Boys with NF-1 also showed greater symmetry between the left and right hemispheres in this region compared with girls with NF-1 and controls, who showed a pattern of left greater than right asymmetry of the PT. Intelligence-based discrepancy scores of reading and math achievement, which are commonly used to define learning disabilities, were significantly related to PT asymmetry in the NF-1 group as a whole. Less leftward asymmetry of the PT was associated with poorer reading and math achievement in relation to intellectual test scores. Conclusions: The high susceptibility of individuals with NF-1 to develop reading and other learning disabilities seems to be related to the development of the sylvian fissure. These results provide further support for the hypothesized association between sylvian fissure morphologic features and learning disabilities.