■ BACKGROUND: Surgical approaches to the round window have become more common in recent years reflecting the increasing use of the round window as a route for insertion of the cochlear implant electrode, placing the floating mass transducer at the round window for direct perilymph vibration, and inner ear drug delivery. In most cases, round window can be accessed directly through facial recess using a posterior tympanotomy.

■ AIM: The aim of this study is to consider how accessible the round window is when approached through a posterior tympanotomy, and to establish a practical classification of such accessibility in order to help clinical decision making.

■ PATIENTS AND METHODS: The access to the Round window was assessed in 50 patients undergoing cochlear implantation. The pre-condition for the assessment was a ‘perfectly’ formed posterior tympanotomy, defined as;1.further enlargement of the posterior tympanotomy anterior-laterally would risk injury to the corda tympani, canal wall or annulus and 2. enlargement of the posterior tympanotomy posteriorly would risk the injury to the facial nerve.

■ RESULT:We classify the access to the round window into three main categories. Type I: the round window can be fully exposed, bony overhang easily removed and round window membrane entirely visualized. Type II is sub-divided into Type IIa and Type IIb. Type IIa: bony overhang can be partially removed, exposing more than 50% but less than 100% of the round window membrane. Type IIb: the exposure of the round window is less than 50% but more than 0%. Type III: no round window membrane can be visualized despite the best surgical effort. Type I and Type IIa access occurred in 72% of cases. 8% had Type III access and these cases were more likely to be associated with temporal bone anomalies.

■ CONCLUSION: In the large majority of cases the round window membrane can be adequately accessed via posterior tympanotomy.