Feasibility of Automated Drilling for Robotic Cochlear Implantation Determined by Pediatric Anatomy

The facial recess (FR) access is the gold standard for cochlear implant (CI) surgery indicated to rehabilitate profound deafness. Recently, robot-assisted and navigation-based keyhole surgeries also use the same FR access to drill an entry toward the inner ear for placing a CI array. In robot-assisted CI surgery (RACIS) with the HEARO system, a 1.8 mm diameter cutting drill is used directly through the FR without damaging the chorda tympani and the facial nerve. To make the leap toward pediatric cases with this system, a thorough knowledge of the developmental anatomy of the FR is essential. Here, we assess the developmental dimensions of FR in children aged 0 to 18 years and determine the feasibility of pediatric RACIS.

Computed tomography (CT) images of the temporal bone scans from 2 boys and 2 girls aged between 0 and 18 years old were retrieved retrospectively. Pathologic scans and abnormal anatomy cases were excluded. The samples were categorized by age groups to evaluate the growth pattern of FR. FR width (FRW), FR angle (FRA), depth of FR (DFR), and direction of FR (DrFR) were assessed with RadiAnt DICOM Viewer. SPSS 24.0 was used for statistical analysis, and P<0.05 was accepted as statistically significant.

CT images of 65 children (mean age: 10.34±4.92), 33 boys and 32 girls, were included in the study. FR depth was significantly greater in boys than in girls (P=0.007), while no significant difference was found between genders in FR dimensions (P>0.05). The FRW and DFR increased progressively from birth until the prepubescent period and remained constant in the postpubescent period (P=0.011). The FRW did not differ between the genders (P>0.05). In the risk assessment using an anatomic facial recess width (FRW) threshold of 2.2 mm (for a minimum 0.4 mm distance for the facial nerve), the highest anatomic risk was observed during infancy (100%), followed by early childhood (81.8%). This risk decreased to below 50% during the prepubescent and postpubescent periods (10 y of age and older).

Our findings demonstrate significant anatomic differences between pediatric and adult populations that may affect the applicability of RACIS. Within the pediatric population, FR dimensions approached adult values during the prepubescent period. Using a facial recess width (FRW) threshold of 2.2 mm, 50% of pediatric cases aged 10 years and older were considered anatomically suitable for RACIS with the current HEARO procedure. However, pediatric robotic surgery may still carry an increased risk of facial nerve injury. Therefore, drill bits with diameters smaller than 1.8 mm should be developed to maintain a safe distance from the facial nerve and improve the safety of pediatric robotic surgery.