Evaluation of round window accessibility to cochlear implant insertion.

Area of Science:

• Otolaryngology
• Neurosurgery
• Medical Engineering

Background:

• Hearing preservation is a key goal in cochlear implantation.
• The round window membrane (RWM) is increasingly utilized as an insertion portal for cochlear implant electrode arrays.
• The St Thomas' Hospital (STH) classification system was developed to assess RWM accessibility for electrode insertion.

Purpose of the Study:

• To prospectively evaluate the STH classification's utility in determining the optimal cochlear implantation route for RWM-intended cases.
• To compare RWM accessibility for electrode insertion between adult and pediatric patients.

Main Methods:

• Prospective cohort study involving consecutive adult and pediatric patients undergoing cochlear implantation.
• RWM visibility was graded using the STH classification after posterior tympanotomy and niche overhang removal.
• Surgical approach (membranous vs. bony cochleostomy) was recorded based on RWM visibility and accessibility.

Main Results:

• Most adults (89%) and children (78%) had adequate RWM exposure (STH Types I and IIa).
• Less RWM exposure (Types IIb and III) was significantly more common in children (p=0.004).
• Successful RWM insertion via membranous cochleostomy was achieved in 96% of Type I and 63% of Type IIa cases, while Type III required conventional bony cochleostomy.

Conclusions:

• The STH classification is a practical tool for correlating RWM visibility with the appropriate cochlear implant insertion route.
• Pediatric patients present greater challenges for RWM electrode insertion compared to adults due to reduced accessibility.