Relationship between polysomnography findings in adults with Type 1 chiari malformation and postoperative decompressive volume

Objective: This study aimed to evaluate changes in polysomnographic (PSG) parameters after posterior fossa decompression in adults with Chiari type I malformation and to investigate the relationship between these changes and the postoperative increase in posterior fossa volume. Materials and Methods: Adult patients with Chiari type I malformation who underwent suboccipital craniectomy, C1 laminectomy, and duraplasty between January 2010 and June 2025 were retrospectively reviewed. A total of 47 patients with available preoperative and postoperative PSG recordings and complete radiological imaging were included. Posterior fossa volume was calculated on non-contrast cranial CT images using a manual ellipsoid formula and by segmentation with 3D Slicer software. From PSG recordings, body mass index, sleep stage durations, total sleep time, sleep efficiency, central apnea count and index, and apnea–hypopnea index were analyzed. Respiratory events were scored according to the 2020 American Academy of Sleep Medicine criteria. Results: The mean age of the patients was 37.8±12.8 years, and 78.7% were female. A significant postoperative increase in N3 sleep duration was observed (106.4±61.2 min vs. 138.0±60.9 min; p=0.008). Total sleep time also increased significantly in the postoperative period (380.3±82.5 min vs. 410.2±60.1 min; p=0.044). Although the central apnea index decreased postoperatively, this change was not statistically significant. An increase in postoperative posterior fossa volume was associated with a reduction in mean central apnea duration (manual measurement r=-0.371, p=0.010; 3D Slicer r=-0.309, p=0.041). In addition, a negative correlation was found between posterior fossa volume measured by 3D Slicer and the apnea–hypopnea index (r=-0.331, p=0.028). Conclusion: In adults with Chiari type I malformation, an increase in posterior fossa volume following decompression surgery is associated with favorable changes in sleep architecture and selected parameters of central sleep-disordered breathing.