Correlation of mastoid pneumatization and pneumatization of the posterior lip of internal auditory meatus and its implications during retrosigmoid craniotomy.

OBJECTIVE

This study aimed to evaluate the relationship between the degree of mastoid pneumatization and the pneumatization of the posterior lip of the internal auditory meatus (IAM) in patients with vestibular schwannoma (VS).

METHODS

A retrospective analysis was performed on 224 patients who underwent retrosigmoid approach for VS excision (2011 to 2021). Mastoid pneumatization was graded based on Han et al classification on computed tomography (CT). Presence of pneumatization of the posterior lip of the IAM was assessed, and its correlation with mastoid and frontal sinus pneumatization, dominance of sigmoid sinus and jugular bulb position was analyzed.

RESULTS

Pneumatization of the posterior lip of the IAM was observed in 39 patients (17.4%). Higher grades of mastoid pneumatization corresponding to grade 3 or 4 were found in 156 (69.6%) of patients. On univariate analysis, Manjila et al type 3 or 4 jugular bulb and higher grade of mastoid pneumatization were associated with pneumatization of the posterior lip of IAM. On multivariate analysis, only higher grade of mastoid pneumatization was independently associated with a pneumatization of the posterior lip of the IAM (OR, p = 0.003). Higher grades of mastoid pneumatization increased the risk of mastoid air cell entry during craniotomy (p = 0.0001) and was linked to postoperative cerebrospinal fluid (CSF) oto-rhinorrhoea.

CONCLUSION

The degree of mastoid pneumatization has a strong independent correlation with pneumatization of the posterior lip of the IAM. Preoperative thin-slice temporal bone CT is essential in cases of extensive mastoid pneumatization to assess the posterior lip of the IAM for potential pneumatization.