Systematic radiographic evaluation of three potential implantation sites for a semi-implantable bone conduction device in 52 patients after previous mastoid surgery.

The aim of this study was the evaluation of three localizations for the implantation of a semi-implantable transcutaneous bone conduction device after previous mastoid surgery. This is a retrospective review of electronic datasets of cranial computed tomography studies. The study setting is one tertiary referral center and included 52 consecutive adult patients (60 temporal bones) with a history of mastoid surgery. The intervention was virtual placement of the device with a planning software within the remaining mastoid as well as dorsal of the sigmoid sinus and caudal of the transverse sinus (retrosigmoidal localization) and dorsocranial of the parietomastoid suture and cranial of the transverse sinus (parietal localization). The main outcome measure included dimensions of the bone for the reception of implant and screws, relative localization of dura mater or sinus sigmoideus, distance to the cochlea, thickness of the epicranium and classification of implantation as possible or impossible. Implantation within the remaining mastoid was deemed possible in 35 mastoid bones (58.3%). The best-suited alternative localization was retrosigmoidal in 22 (42.3%) and parietal in 29 patients (55.8%). The mean distance from the implantation site to the cochlea was lowest with on average 41.2 ± 3.1 mm from within the remaining mastoid. The differences in distance from the cochlea to the alternative localizations were each statistically significant (p < 0.01, ANOVA/Bonferroni t test). The retrosigmoidal and parietal localizations are suitable alternative implantation sites. The application of spacers may prevent contact to the sinuses or dura. Preoperative CT-based planning is recommended in cases of previous mastoid surgery. LEVEL OF EVIDENCE: 4 (case series).