Congenital Inner Ear Malformations as a Cause of Single Sided Deafness

Abstract

Learning Objectives: To understand the relationship with concurrent clinically significant inner ear abnormalities (IEMs) and single sided deafness (SSD). To increase awareness of the functional impact of SSD and its radiological findings which may influence the treatment of this condition. To interpret the treatment modalities of SSD by the help of radiological data and find out which IEMs constitute a contraindication to cochlear implantation. Introduction: Single sided deafness (SSD) was a negligible entity until recently because of normal language development by the help of contralateral normal hearing. A Number of studies revealed that many SSD cases had concurrent inner ear malformations (IEM) which may influence the treatment plan of SSD. The aim of this study was to elucidate the prevalence and distribution of IEMs in congenital SSD which is crutial for the treatment. Method(s): This is a retrospective study of temporal boneCTand MRI findings of 77 consecutive patients 0-18 years old with congenital SSD. Cases with acquired etiology were excluded. On MRI; the diameter, and signal intensity of the cochlear nerve (CN) were compared to the ipsilateral facial nerve. Also the width of the BCNC was measured on axial CT and it was defined as "stenotic"if the width was less than 1.5 mm. The diagnosis of pediatric SSD is initially verified by pure-tone audiometry or ABR. Result(s): 40 cases had normal CT&MRI findings whereas the remaining 37 had various IEMs. The most common pathology was BCNC stenosis/atresia together with CN deficieny(CND) seen in 27(72%) of the subjects. Interestingly this stenotic/atretic BCNC is seen in otherwise normal cochlear morphology which can be termed as ''isolated aperture atresia/stenosis''. Next in frequency were cochlear hypoplasias followed by incomplete partition I with 6 and 2 patients respectively. The most unexpected finding of the present studywas the exceptionally high prevalence of CND accompanied by isolated BCNC stenosis/atresia as a cause of SSD rather than other IEMs. Conclusion(s): All cases with SSD should have a CT in addition to MRI scan, because the prevalanceof BCNC anomalies with CND is very high in SSD.Since the non-functioning hypoplastic or aplastic CN together with BCNC atresia is a contraindication for CI, management of these patients is complex and BAHA could be an option.Cases with SSD should not be implanted before detailed evaluation of BCNC and CN.