Rostral brain axonal injury in congenital central hypoventilation syndrome

Brain injury underlying the state-related loss of ventilatory drive, autonomic, cognitive, and affective deficits in congenital central hypoventilation syndrome (CCHS) patients appears throughout the brain, as demonstrated by magnetic resonance (MR) T2 relaxometry and mean diffusivity studies. However, neither MR measure is optimal to describe types of axonal injury essential for assessing neural interactions responsible for CCHS characteristics. To evaluate axonal integrity and partition the nature of tissue damage (axonal vs. myelin injury) in CCHS, we measured water diffusion parallel (axial diffusivity) and perpendicular (radial diffusivity) to rostral brain fibers, indicative of axonal and myelin changes, respectively, with diffusion tensor imaging (DTI). We performed DTI in 12 CCHS (age 18.5 + or - 4.9 years, 7 male) and 30 control (17.7 + or - 4.6 years, 18 male) subjects, using a 3.0-Tesla MR imaging scanner. Axial and radial diffusivity maps were calculated, spatially normalized, smoothed, and compared between groups (analysis of covariance; covariates, age and gender). Significantly increased radial diffusivity, primarily indicative of myelin injury, emerged in fibers of the corona radiata, internal capsule, corpus callosum, hippocampus through the fornix, cingulum bundle, and temporal and parietal lobes. Increased axial diffusivity, suggestive of axonal injury, appeared in fibers of the internal capsule, thalamus, corona radiata, and occipital and temporal lobes. Multiple brain regions showed both higher axial and radial diffusivity, indicative of loss of tissue integrity with a combination of myelin and axonal injury, including basal ganglia, bed nucleus, and limbic, occipital, and temporal areas. The processes underlying injury are unclear, but likely stem from both hypoxic and developmental processes.