Postoperative Cochlear Ossification after Retrosigmoid Resection of Vestibular Schwannoma

Objective: Vestibular schwannomas (VSN) account for the vast majority of lesions located in the cerebellopontine angle (CPA). The goals of vestibular schwannoma surgery are intact facial nerve function and preservation of cochlear nerve function, if possible total tumor removal. In cases of pre- or postoperative deafness, restoration of hearing with auditory brainstem implant (ABI) or cochlea implant (CI) is a promising treatment option with normally better results in CI than in ABI. The aim of this retrospective study is to evaluate cochlear ossification or obliteration secondary to a retrosigmoid approach, which is important for later CI implantation especially in single-sided deafness.

Materials and Methods: We retrospectively reviewed data from our suboccipital retrosigmoid operation database for the period from January 2008 to February 2015 with sufficient MRI examinations. A total of 70 patients could be analyzed retrospectively. The patient´s data (age, gender, side of operation, tumor entities and the duration of follow up) were evaluated. For the evaluation of cochlea, the most recent T2-weigted MRI exams were taken into account. After the primary evaluation we decided to improve the evaluation accuracy through the reconstructed MR examinations of inner ear.

Results: In our survey, 24 out of 70 (34%) patients had cochlear obliteration. The male/female ratio is 0.8, which is not significantly different. The median follow-up is 28.5 months. The median patients’ age is 51.5 years.

Conclusion: Although in our preliminary MRI evaluation a seductive result of only 7% cochlear obliteration could be achieved it had to be corrected after substitution of conventional T2-Weigted MRI examinations through high-resolution-data, which were reconstructed and reformatted in our MRI department. 34% of suboccipital approaches manifested cochlear obliteration to some extent. Therefore, the aim of the study could not be reached. Nevertheless, it still remains unclear to what extent the cochlear fibrosis impedes the CI implantation, which can be the topic of further studies.