Usefulness of the radiological planning for hearing preservation surgery in vestibular schwannoma

PURPOSE: During vestibular schwannoma surgery there is a risk of endolymphatic duct and sac injury, which may cause a loss or a deterioration of hearing. The goal of the study was to evaluate the empirical utility of presurgical planning using CT with the bone window for the hearing preservation surgery. METHODS: The study was performed on 14 human temporal bones. CT scans with the bone window were obtained in the standard position. Safe drilling line was evaluated and after that drilling distances were analysed: the lateral drilling distance, total length of internal acoustic meatus, drilled length of internal acoustic meatus. After this, a surgical exposure was performed, using size of a drill tip as measuring scale. The dura was excised and endolymphatic duct was injected with a latex. Revision of the internal acoustic meatus was performed with the use of a microscope. RESULTS: Mean results of safe drilling coefficients were: lateral drilling distance: 10 ± 2 mm, total length of internal acoustic meatus: 9 ± 2 mm, drilled length of internal acoustic meatus: 7 ± 2 mm. In all cases, no endolymphatic duct injury was observed. CONCLUSIONS: Preoperative radiological planning using the safe drilling coefficients is of value for the hearing preservation surgery in vestibular schwannoma. The size of the drilling tip may be used as an intraoperative measuring scale during this procedure. However, CT with a bone window is a necessary tool for the purposes of this procedure.