■ BACKGROUND: In the1970s and 80s the round window was the common route for insertion of the multi-array cochlea implant electrode. However there were concerns of potential trauma to the osseous spinal lamina, hence an osseous cochleostomy approach was favoured. Anatomical reconstructive studies and insertion experiments carried out recently with the new breed of electrodes suggested that insertion through the round window may offer an alternative with less risk of trauma.

■ OBJECTIVES: To compare the result of the round window insertion with that of conventional cochleostomy in patients who underwent cochlear implantation for combined electrical-acoustic  stimulation (EAS).

■ METHODS: MED-EL C40+M electrodes were introduced via a round window membrane cochleostomy in 3 patients, and by a conventional osseous cochleostomy in 5 patients. For the round window insertion, the round window area was visualised through the posterior tympanotomy, the overhang of the niche was removed with a low velocity burr to display the round window membrane. A partial circumferential incision was made anterior-inferior in the membrane. The conventional cochleostomy was made 1 mm anterior and inferior to the round window. The precautions recommended for EAS surgery were applied to both approaches. A post-operative CT scan was performed in all patients to assess the location of the electrode.

■ RESULT: Insertion of the electrode was achieved without resistance in all round window and osseus cochleostomy patients.Functional hearing preservation was achieved in 7 out of 8 patients.One patient (osseus cochleostomy insertion) lost a significant amountof residual hearing and did not benefit from the cochlear implant. One patient in each group showed deterioration of their residual hearing at 12 month after initial device fitting. All seven patients benefit from EAS. The post-operative CT scans suggests that the round window insertion is associated with a more peri- modiolarnlocation in the proximal basal turn.

■ CONCLUSION: Round window approach can achieve atraumatic electrode insertion for EAS.