Inner Ear Anomaly with Atypical Incomplete Partition “Type 1. 5” - A Case Report

Abubakar A

Published on: 2021-04-23

Abstract

Introduction: Cochleovestibular anomalies are a spectrum of deformed inner ear structures. Incomplete partition (IP) is a common form, which includes three subtypes. Atypical form of incomplete partition is descryed in this work.

Patient: A 14-year-old male presented with a right-side sensorineural hearing loss was diagnosed to have atypical form of IP.

Intervention: Diagnosis was made with magnetic resonant imaging and audiological evaluation.

Main outcome measure: To compare our findings with the reported forms of IP.

Result: We reported an atypical form that did not mentioned before in literature and called it IP type 1.5.

Conclusion: The classifications available now in literature are still unsatisfactory. Congenital inner ear anomalies are spectrum of malformation rather than separate entities.

Keywords

Inner ear anomalies; Incomplete Partition

Introduction

It was estimated that congenital inner ear malformations account for 20% of children with sensorineural hearing loss (SNHL)[1, 2] Inner ear is susceptible to a variety of congenital malformation based upon the timing of embryogenesis at which an insult occurred. In 1987, Jackler ^[3]. were the first to classify inner ear malformation using polytomography and considering the timing of developmental arrest starting from the 3rd week to the 7th week of gestation. They classified inner ear malformation into labyrinthine aplasia, common cavity, cochlear aplasia, cochlear hypoplasia, and incomplete partition. In 2002, Sennaroglu and Saatci^[4]. proposed another detailed classification based on computed tomography (CT) with further subdivision of incomplete partition. Incomplete partition (IP) is divided into three types. IP type 1 entails cystic cochlea with completely absent modiolus and marked dilated vestibule. IP type 2 (Mondini dysplasia) entails normal basal turn with cystic fusion of the middle and apical cochlear turns, mildly dilated vestibule, and large vestibular aqueduct (LVA). IP type 3 is X-linked. [5, 6]

Case Report

A 16-year-old male presented to the Otolaryngology Department, Tanta University with a right-side hearing loss of unidentifiable onset. The actual onset was not clear, but it seemed to be of long duration with negligence from the patient and his family to seek medical advice. History taken regarding prenatal, natal, and postnatal insults were irrelevant. The patient was born during an uneventful vaginal delivery. He received immunizations according to the Egyptian Local Immunization Schedule. All his developmental milestones were excellent including the speech development. The family history was irrelevant as regard hearing loss. Otological examination revealed no apparent external or middle ear deformities. Tuning fork test revealed a right side false negative Rinne test (false hearing of the bone conduction better than air conduction, as the bone conduction was appreciated falsely by the left ear) and a left side Rinne positive. Weber’s test was lateralized to the left ear (normal one). Otherwise, otolaryngology examination was free. All the previous data suggested a right-side SNHL at least of severe degree. Audiological evaluation (Figure 1) revealed right-side severe SNHL with poor speech discrimination and within normal hearing of the left ear. Tympanometry was type A bilaterally with absent acoustic reflex in the right ear. The previous data of unilateral SNHL was suggestive of a retrocochlear lesion on the right side, so we proceeded with magnetic resonance imaging (MRI) with contrast on the temporal bone and the cerebellopontine angle (CPA). The MRI was surprising, as there was a right-side inner ear malformation, CPA was free, and the left-side cochlea was normally developed. MRI of the right inner ear showed normally developed cochlear basal turn (Figure 2), fused middle and apical turns (Figure 3), marked dilation of the vestibule, and distorted lateral semicircular canal (SCC) (Figure 4). The endolymphatic duct and sac were of normal diameter. The internal auditory canal documented the presence of the cochlear nerve (Figure 3).

Figure 1: Audiological evaluation showing right severe sensorineural hearing loss with poor speech discrimination and absent stapedial reflex. (Note there is some residual hearing).

Figure 2: Temporal bone magnetic resonance imaging showing developed basal turn of the right cochlea which is differentiated into scala vestibule (anterolateral) and scala tympani (posteromedial).

Figure 3: Temporal bone magnetic resonance imaging showing fused middle and apical turns of the right cochlea together with the presence of the cochlear nerve.

Figure 4: Temporal bone magnetic resonance imaging showing marked dilated vestibule with dysplastic lateral semicircular canal.

Discussion

Incomplete partition type 1 entails completely absent modiolus with cystic cochlea without the development of any cochlear turns, marked dilated vestibule, and dysplastic SCCs. [7] Since the cochlea is not developed, the cases developed total hearing loss since birth and gain little benefit from traditional hearing aids. Cochlear implantation is the best option for hearing rehabilitation [8-13]. Incomplete partition type 2 entails normally developed modiolus at the basal cochlear turn, cystic fusion of the middle and apical turns due to deficient modiolus, leading to one and half turns cochlea instead of two and half turns, together with mildly dilated vestibule, normal SCCs, and large vestibular aqueduct (LVA).[7, 14]. Since there is basal cochlear development, the cases showed some degree of residual hearing.^[15]. In incomplete partition type 3, the cochlea has the interscalar septa with completely absent modiolus. The cochlea is displaced posteriorly to be located directly at the lateral end of the IAC. [5, 16]. The novelty of our case is that it retains some criteria from IP type 1 and some other criteria from IP type 2. To be considered IP type 1, positive findings include marked dilation of the vestibule, dysplastic lateral SCC, and normal endolymphatic duct size, however, negative findings include normal developed basal cochlear turn and the presence of some residual hearing. To be considered IP type 2, positive findings include normal developed basal cochlear turn, cystic fusion of the middle and apical turns, dilated vestibule, and the presence of residual hearing, however, negative findings include dysplastic lateral SCC and normal size endolymphatic duct. In our case, the presence of residual hearing can be explained by the development of the basal cochlear turn which was documented in MRI by the presence of scala tympani and scala vestibule We assume that in our case the inner ear development was arrested somewhen in between IP type 1 and type 2, hence, we called it IP type 1.5.

Conclusion

Incomplete partition spectrum is one of the commonest inner ear malformations. Sennaroglu and Saatci classification [4]. for inner ear anomalies is the most widely used classification. It seems that this classification needs to be updated to include other atypical cases and further studies of cochlear development need to be done. Congenital inner ear anomalies are a spectrum of malformation rather than separate entities.

International Journal of Rhinology and Otology