Consequences of Mastoidectomy on Bone Conducted Sound Based on Simulations in a Whole Human Head.

HYPOTHESIS: The aim of this study is to investigate how a mastoidectomy surgery affects bone conduction (BC) sound transmission using a whole head finite element model.

BACKGROUND

Air conduction (AC) and BC hearing thresholds are normally used to evaluate the effect of an ear surgery. It is then assumed that the BC hearing thresholds are unaffected by the surgery. Moreover, BC hearing aids are used in cases of unilateral or conductive hearing loss in heads that have undergone a mastoidectomy surgery. Given the invasiveness of the surgery, the BC hearing sensitivity may be altered by the surgery itself.

METHODS

Two types of mastoid surgery, canal wall up and canal wall down, with and without obliteration, were simulated in a whole head finite element model for BC stimulation, the LiUHead. The evaluations were conducted for two different methods of applying the BC sound, at the skin surface (B71 transducer) and directly at the bone (BC hearing aid).

RESULTS

The results showed that a mastoidectomy surgery increased the cochlear vibration responses with BC stimulation. The increase was less than 5 dB, except for a canal wall down surgery which gave an increase of up to 8 dB at frequencies close to 10 kHz. The increase was greater at the ipsilateral cochlea compared with the contralateral cochlea.

CONCLUSION

A mastoidectomy surgery increases the vibration at both cochleae for BC stimulation and the increase generally improved with frequency. Obliteration of the surgical cavity does not influence BC sound transmission.