Abstract: Objective To explore the relationship between the degree of mastoid pneumatization and the development of the endolymphatic sac. Methods A retrospective study of 145 patients(290 ears)who underwent temporal bone CT examination from January 2019 to May 2021 in the Department of Otolaryngology. After screening, the patients were divided into the well- pneumatized and the poorly-pneumatized groups, according to the degree of mastoid pneumatization. The 1∶1 closest match was adopted. The propensity score(PS)was set at 0.02. The propensity score matching(PSM)analysis was performed on covariates based on age and otitis media. The analysis produced 58 sets of paired data. The shortest distance between the middle of the posterior semicircular canal and the posterior edge of the posterior petrous surface(P-P value)was used to indirectly reflect the development of the endolymphatic sac. The shortest distance between the middle of the posterior semicircular canal and the posterior edge of the posterior petrous surface(P-P value)of different degrees of pneumatization was analyzed statistically. Results The median(interquartile range)of the shortest distance between the middle of the posterior semicircular canal and the posterior edge of the posterior petrous surface(P-P value)was 2.26(1.49, 3.08)mm. The difference between the degree of mastoid pneumatization and the shortest distance between the middle of the posterior semicircular canal and the posterior edge of the posterior petrous surface(P-P value)was not statistically significant. That is, the degree of mastoid pneumatization was not associated with the development of the endolymphatic sac. There were no statistically significant differences in the general data processed after PSM in the two mastoid pneumatization groups. That is, the propensity score matching was effective in managing the selection deviation of non-random experimental data in clinical research. There was a statistically significant difference in the degree of mastoid pneumatization and otitis media; in the group with good mastoid pneumatization, the incidence of otitis media is lower. Conclusion There is no correlation between the degree of mastoid pneumatization and the development of the endolymphatic sac.

Key words: Endolymphatic sac development, Degree of mastoid pneumatization, The shortest distance between the middle of the posterior semicircular canal and the posterior edge of the posterior petrous surface, Propensity score matching, Gem energy spectrum CT