Altered global and regional brain mean diffusivity in patients with obstructive sleep apnea

Abstract

Obstructive sleep apnea (OSA) is a common and progressive disorder accompanied by severe cardiovascular and neuropsychological sequelae, presumably induced by brain injury resulting from the intermittent hypoxia and cardiovascular processes accompanying the syndrome. However, whether the predominant brain tissue pathology is acute or chronic in newly-diagnosed, untreated OSA subjects is unclear; this assessment is essential for revealing pathological processes. Diffusion tensor imaging (DTI)-based mean diffusivity (MD) procedures can detect and differentiate acute from chronic pathology and may be useful to reveal processes in the condition. We collected four DTI series from 23 newly-diagnosed, treatment-naïve OSA and 23 control subjects, using a 3.0-Tesla magnetic resonance imaging scanner. Mean diffusivity maps were calculated from each series, realigned, averaged, normalized to a common space, and smoothed. Global brain MD values for each subject were calculated using normalized MD maps and a global brain mask. Mean global brain MD values and smoothed MD maps were compared between groups by using analysis of covariance (covariate: age). Mean global brain MD values were significantly reduced in OSA compared with controls (P = 0.01). Multiple brain sites in OSA, including medullary, cerebellar, basal ganglia, prefrontal and frontal, limbic, insular, cingulum bundle, external capsule, corpus callosum, temporal, occipital, and corona radiata regions showed reduced regional MD values compared with controls. The results suggest that global brain MD values are significantly reduced in OSA, with certain regional sites especially affected, presumably a consequence of axonal, glial, and other cell changes in those areas. The findings likely represent acute pathological processes in newly-diagnosed OSA subjects.

Figure 1

Medullary, cerebellar, temporal, basal-ganglia, and limbic brain areas with reduced MD values in OSA over control subjects. Multiple brain areas, including the dorsal (a), ventral (e), and ventrolateral medulla (f), cerebellar uvula (b), cerebellar crus I and II (c, g), middle and inferior cerebellar peduncles (d), ventrolateral temporal lobe (h), dorsal temporal white matter and occipital cortex (i), ventral (k) and mid hippocampus (n), putamen (j), and insular cortex (m), showed reduced MD values in OSA compared to control subjects. All brain images are shown in neurological convention, with the left side of the brain on left side of the axial and coronal images (L = Left, R = Right), and color bar represents t-statistic values.

Figure 2

Thalamic, corpus callosum, frontal, occipital, cingulate, and corona radiata regions with decreased MD values in OSA over control subjects. Brain regions with decreased MD values in OSA emerged in thalamic areas (a, c), external capsule (b), anterior corpus callosum (d), frontal (e) and occipital (f) white matter, prefrontal cortex (g), mid and posterior cingulate cortices and cingulum bundle (h, i), and anterior (j), mid (k), and posterior (m) corona radiata. Figure conventions are the same as in Figure 1.