Körner's septum as a determinant of the tympanic facial nerve-stapes relationship and epitympanic anatomy: a CT-based morphometric analysis and risk stratification model.

OBJECTIVE: To quantitatively evaluate the impact of Körner's septum (KS) and cog morphology on the tympanic facial nerve-stapes relationship and epitympanic spatial configuration, focusing on the minimum distance between the tympanic segment of the facial nerve (TFN) and the stapes footplate, anterior epitympanic recess (AER) volume, and associated anatomical variations. METHODS: A total of 498 temporal bones were evaluated from 249 patients, including 116 women (46.6%) and 133 men (53.4%), with equal distribution between sides (249 right and 249 left). TFN-stapes distances (axial, coronal, and minimum), AER volume, cog length, and the presence of TFN prolapse and dehiscence were assessed. A novel Surgical Corridor Constraint Index (SCCI) was developed to stratify the surgical difficulty regarding access to the oval window niche. RESULTS: The presence of KS was associated with a significant reduction in the minimum TFN-stapes distance (e.g., in the cog-incomplete subgroup: 0.90 ± 0.22 mm vs. 1.44 ± 0.44 mm, p < 0.001) and a marked decrease in AER volume (e.g., in the cog-complete subgroup: 13.97 ± 5.70 mm³ vs. 24.61 ± 7.18 mm³, p < 0.001). CONCLUSION: Körner's septum is a significant radiological determinant of the tympanic facial nerve-stapes relationship and epitympanic anatomy, significantly narrowing the TFN-stapes distance, reducing AER volume, and increasing the likelihood of TFN prolapse. The proposed SCCI represents a preliminary, hypothesis-generating framework for describing anatomical constraints in the oval window region and requires external and intraoperative validation. Collectively, these findings highlight the potential relevance of KS to preoperative anatomical assessment, supporting the integration of imaging-based anatomical assessments in otologic surgery.