Comparison of Cochlear Implant Relevant Anatomy in Children Versus Adults

Abstract

Hypothesis To test whether there are significant differences in pediatric and adult temporal bone anatomy as related to cochlear implant (CI) surgery Background Surgeons rely upon anatomical landmarks including the round window (RW) and facial recess (FR) to place CI electrodes within scala tympani. Anecdotally, clinicians report differences in orientation of such structures in children versus adults. Methods IRB approval was obtained. High resolution CT scans of 24 pediatric patient (46 ears) and 20 adult patients (40 ears) were evaluated using software consisting of a of a model-based segmentation algorithm that automatically localizes and segments temporal bone anatomy (e.g. facial nerve, chorda tympani, external auditory canal (EAC), and cochlea). On these scans, angles pertinent anatomy were manually delineated and measured blinded as to the age of the patient. Results The EAC and FR were more parallel to the basal turn (BT) of the cochlea in children versus adults (∠EAC:BT 20.55 ° vs. 24.28°, p = 0.003; ∠FR:BT 5.15° vs. 6.88°, p=0.009). And, the RW was more closely aligned with the FR in children versus adults (∠FR:RW 30.43° vs. 36.67°, p=0.009). Comparing the lateral portion of the EAC (using LatEAC as a marker) to the most medial portion (using ⊥TM as a marker), the measured angle in children was 136.57° and 172.20° in adults (p<0.001). Conclusion There are significant differences in temporal bone anatomy of children versus adults pertinent to CI electrode insertion.

Predicting Round Window Niche Visibility via the Facial Recess Using High-Resolution Computed Tomography

“…This finding is consistent with the fact that surgeons often describe cochlear implantation as being more difficult in the pediatric population than in the adult population (10) and evidence that RWM visibility is worse in children (8). Furthermore, several studies compared the temporal bone anatomy of adults and children in relation to cochlear implantation and showed that facial recess width is not significantly different between children and adults (10Y14), consistent with our result.…”

“…These parameters can affect FN location and should be studied in a large cohort. Finally, our finding that EAC angle is significantly wider in adults is consistent with the report by McRackan et al (10). Assuming that the EAC maintains the same angle relative to the sagittal plane irrespective of age, the Lloyd et al (17) report also supports our observation.…”

“…However, Lloyd et al (17) reported that the angle between the basal turn and the midsagittal plane decreases with age, and McRackan et al (10) suggested that the change in the angle between the facial recess and the basal turn is related to age. These parameters can affect FN location and should be studied in a large cohort.…”

Impingement of the Carotid Canal on the Basal Turn of the Cochlea as Pertaining to Cochlear Implantation

“…This finding is also supported by the study by Martinez-Monedero et al (9), which states that age does not affect the dimensions of the cochlear base. In contrary, McRaken et al (25) found significant differences in temporal bone anatomy (e.g., the angle of external auditory canal, facial recess tympanic membrane, and ideal drilling trajectory for cochleostomy with the basal turn of the cochlea) between children and adults.…”

“…A surgeon depends heavily on anatomy knowledge of the cochlea to estimate structures hidden by bone (25). Thus, the preoperative topographic information of the cochlea and the carotid canal, such as impingement of the carotid canal on the anterior cochlear wall (8.6% cases) and the carotid canal abutting the anterior cochlear wall (5.2% cases), may assist in the interpretation of the patient's radiology, selection of ear to be implanted, and operative strategy for atraumatic cochlear implant insertion.…”