Orbital soft-tissue remodeling after bony decompression in thyroid-associated orbitopathy: a CT-based analysis of extraocular muscles volume

The study evaluated changes in extraocular muscles (EOMs) following orbital decompression in patients with thyroid-associated orbitopathy (TAO) using computed tomography (CT)–based volumetric analysis. Patients who underwent orbital decompression with available preoperative and postoperative orbital CT scans were retrospectively reviewed. Decompression procedures were classified as medial, inferomedial, balanced, or three-wall decompression. Volumes of individual EOMs were calculated from coronal CT images, and temporal changes were assessed by locally estimated scatterplot smoothing regression, with associated clinical factors analyzed using multivariate linear regression. A total of 307 orbits from 171 patients were analyzed. Medial rectus muscle volume increased significantly across all surgical groups, while superior rectus volume decreased after three-wall decompression and inferior rectus volume decreased following medial and balanced decompression. EOM volumetric changes stabilized approximately 150 days postoperatively. Female sex, prior high-dose intravenous (IV) steroid therapy, and prolonged duration of TAO were independently associated with increased postoperative EOM volume, whereas smoking showed a borderline association. These findings indicate that orbital decompression induces distinct and time-dependent EOM volumetric changes, reflecting postoperative soft-tissue remodeling influenced by specific clinical factors.