A Three-Dimensional Geometric-Morphometric Study to Quantify Temporal Bone Growth and its Consequences for the Success of Implanting Bone Anchored Hearing Devices.

OBJECTIVE: A computed tomography (CT)-based morphological-investigation to describe temporal bone growth and to devise a predictive test of the likely success of Bonebridge implantation into the growing mastoid region of the temporal bone in young patients.

STUDY DESIGN: Retrospective cross-sectional study.

SETTING: University Hospital Halle (Saale), Germany.

PATIENTS: Two cohorts participated. This first, of patients aged less than 21 years, comprised 42 men, and 33 women patients. The second cohort, for those aged more than or equal to 21 years, comprised 17 men, and 20 women patients.

INTERVENTION: One hundred eighty three three-dimensional (3-D) reconstructions of the mastoid portion of the temporal bone without malformations or chronic middle ear disease were created on the base of high resolution computer tomography. The 3-D-reconstructions were analyzed using 13 linear measurements and volumetry.

PRIMARY OUTCOME MEASURE: A CT/3-D model derived metric with which to best estimate the likely success of fitting a Bonebridge.

RESULTS: Volume increase stagnated at, on average, 15.6 years of age (men), or 17.5 years (women). The most obvious extent of growth was observed in the craniocaudal direction from the middle cranial fossa to the tip of the mastoid process (total height). This growth is highly correlated with the increase of the mastoid volume (r = 0.938) and thus represents the most influential factor on mastoid volume increase. The total height of the mastoid portion can be used to usefully predict the chance of successful Bonebridge implantation.The depth of the mastoid almost doubled its size from birth (8.93 mm) to adulthood (16.34 mm) and also strongly affects the mastoid volume (r = 0.912). That portion between the external auditory canal (EAC) and the sigmoid sinus showed a lower growth capacity.

CONCLUSIONS: The highly significant correlations between CT derived linear parameters and Bonebridge fitting (p < 0.001) can be used to estimate the success of Bonebridge implantation. The remarkable inter-individual variation of mastoid shape underlines the necessity of radiological preoperative planning.