4 DISCUSSION
4.1 Synopsis of key findings
In this study, we detailed the clinical manifestations, genetic results and audiological features of four patients with BOR syndrome who accepted CI. Auditory and speech performance after CI may vary postoperatively. In addition, the surgery of case 2 was most challenging as with aural atresia.
4.2 Comparisons with other studies
CI outcomes in patients with ROR syndrome were scarcely documented in the literature, because it accounts for only about 2% profound hearing loss(1). Most surgical process reported in the literature seemed normal, no further details were provided(2-5). A perilymphatic gusher was reported in one adolescent case with bilateral dilated vestibule, enlarged vestibular aqueduct, ossicular anomalies, and bilaterally deviated facial nerves. However, this was easily controlled by conventional methods(3).
But there were challenging case report due to ear deformity. Absent temporal bone structures including the lateral semicircular canal, incus and stapes, and oval windows were mentioned in previous case reports, then it took more time to expose the cochlea(6). Patient with aural atresia is most challenging, because few anatomical landmarks were present and the dura might get exposed during mastoidectomy as intraoperative complications. Previous imaging study had showed that non-pneumatized mastoid, antrum and low lying tegmen were very common in BOR. Thus, restricted transmastoid access should be anticipated (7).
Furthermore, aberrant courses of facial nerve definitely makes the operation more difficult(6). Residual soft tissue resembling the nerve definitely increased operating time, such as in case 2. Thus facial nerve monitoring were essential. It is important to not cut any soft tissue too hastily. Finally, malformed cochlea also made precise location of the scala tympany and insertion difficult. Full insertion was unattainable. Cochleostomy was sited more anterosuperior to the round window niche than usual as a result of rotated cochlea, such as in case 3(6). Intraoperative navigation CT may be helpful with cochlear location in such patients.
Most previous studies reported promising outcomes no matter in pediatric(4, 8), adolescent(3) or adult patients(5). Morisada reported 4 in 11 patients who didn’t show good effect without details(8). In this study, we observe unfavorable CI outcomes in three patients. Dysplasia of cochlear nerve is the main reason (9), which was rarely mentioned before. Cochlear implant in children with CND, especially those with CN aplasia, has been controversial. Oblique sagittal high-resolution MRI is routinely performed to screen CND in most CI centers, although it’s not the golden standard test due to limited resolution. Audiological effective cases indicate that certain children do benefit from CI despite of radiographic CND. Thus preoperative communication with CI candidates and their families are essential to help them establish reasonable expectations.
4.3 Strengths and limitations of the study
This study is the first to describe the correlation between CND and CI outcomes in patients with BOR syndrome. However, because of the limited number of cases (only four patients) in this study, our speculation is not conclusive. As BOR syndrome is a disease with extremely low prevalence, large-scale meta-analyses are essential to clearly delineate the correlation between CND, audiological features and CI outcomes.
5 . CONCLUSION
BOR syndrome patients with profound hearing loss could benefit from cochlear implantation. the surgery is challenging in the presentence of complex ear malformations. CI outcomes may be affected by dysplasia of cochlear nerve.