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Introduction: Obstructive sleep apnea (OSA) patients show hippocampal-related autonomic and neurological symptoms, including impaired memory and depression, which differ by sex, and are mediated in distinct hippocampal subfields. Determining sites and extent of hippocampal sub-regional injury in OSA could reveal localized structural damage linked with OSA symptoms.

Methods: High-resolution T1-weighted images were collected from 66 newly-diagnosed, untreated OSA (mean age +/- SD: 46.3 +/- 8.8 years; mean AHI +/- SD: 34.1 +/- 21.5 events/h;50 male) and 59 healthy age-matched control (46.8 +/- 9.0 years; 38 male) participants. We added age-matched controls with T1-weighted scans from two datasets (IXI, OASIS-MRI), for 979 controls total (426 male/46.5 +/- 9.9 years). We segmented the hippocampus and analyzed surface structure with "FSL FIRST" software, scaling volumes for brain size, and evaluated group differences with ANCOVA (covariates: total-intracranial-volume, sex; P < .05, corrected).

Results: In OSA relative to controls, the hippocampus showed small areas larger volume bilaterally in CA1 (surface displacement <= 0.56 mm), subiculum, and uncus, and smaller volume in right posterior CA3/dentate (>= - 0.23 mm). OSA vs. control males showed higher bilateral volume (<= 0.61 mm) throughout CA1 and subiculum, extending to head and tail, with greater right-sided increases; lower bilateral volumes (>= - 0.45 mm) appeared in mid- and posterior-CA3/dentate. OSA vs control females showed only right-sided effects, with increased CA1 and subiculum/uncus volumes (<= 0.67 mm), and decreased posterior CA3/dentate volumes (>= - 0.52 mm). Unlike males, OSA females showed volume decreases in the right hippocampus head and tail.

Conclusions: The hippocampus shows lateralized and sex-specific, OSA-related regional volume differences, which may contribute to sex-related expression of symptoms in the sleep disorder. Volume increases suggest inflammation and glial activation, whereas volume decreases suggest long-lasting neuronal injury; both processes may contribute to dysfunction in OSA.