A novel imaging scoring method for identifying facial canal dehiscence: an ultra-high-resolution CT study

Abstract

ObjectivesFacial canal dehiscence (FCD), typically found in the tympanic segment, is a risk factor for facial nerve injury. An imaging scoring method was proposed to identify FCD based on ultra-high-resolution CT.MethodsForty patients (21 females and 19 males, mean age 44.3 ± 17.4 years), whose tympanic facial canal (FC) was examined during otological surgery, were divided into the FCD group (n = 29) and the control group (n = 11) based on surgical findings. Imaging appearance of tympanic FC was scored 0–3: 0 = no evident bony covering, 1 = discontinuous bony covering with linear deficiency, 2 = discontinuous bony covering with dotted deficiency, and 3 = continuous bony covering. Both lateral and inferior walls were assigned a score as LFCD and IFCD, respectively. An FCD score was calculated as LFCD + IFCD. The diagnostic value of the FCD score was tested using the ROC curve.ResultsThe inter-observer agreement was moderate for the lateral wall (Cohen’s κ coefficient 0.416, 95% CI 0.193–0.639), and good for the inferior wall (Cohen’s κ coefficient 0.702, 95% CI 0.516–0.888). In the FCD group, the most common appearance for both walls was discontinuous bony covering with linear deficiency (LFCD = 1, 22/29, 75.9%; IFCD = 1, 15/29, 51.7%). An FCD score of less than 4 was associated with high sensitivity (0.82) and specificity (0.93) for identifying FCD, with an AUC of 0.928.ConclusionsUsing the proposed scoring method, FCD score < 4 could identify FCD of the tympanic segment with high concordance with surgical findings.Key Points• Imaging appearance of the tympanic facial canal (FC) is divided into four types based on ultra-high-resolution CT images.• The most common appearance of FC with facial canal dehiscence (FCD) is discontinuous bony covering with linear deficiency.• An FCD score, consisting of scores of the lateral and inferior walls, less than 4 is highly indicative of FCD.