Objective To study a distinct type of cochlear malformation,differentiated by its radiological feature,from the current Sennaroglu's classification criteria along with its clinical manifestations.Methods By analyzing the radio-logical findings from high-resolution CT(HRCT)of the temporal bone and 3D-dimensional magnetic resonance imaging(3D-MRI)of the inner ear in 11 cases(13 ears)with special cochlear malformations,we summarized the characteristics of this type of cochlear deformity.Results ① The radiological features of this type of cochlear malformation showed that only a part of the cochlear basal turn originated ventrally from the vestibule,with no or only partial inward turning.There were no upper,middle,or apical turns(cochlea with less than 0.5 turns),and the modiolus and interscalar septa were absent.On HRCT axial images,there was no connection observed between the cochlea and the internal auditory canal(IAC).MRI results consistently showed a cochlear nerve deficiency(CND),with audiometric findings indicating complete hearing loss.Most cases were accompanied by abnormally developed vestibules and malformed semicircular canals,and the cochlea on the opposite side often had severe malformations as well.② Based on the imaging characteristics,this type of cochlear malfor-mation,with only partial development of the basal turn(cochlea with less than 0.5 turns),was categorized as cochlear hy-poplasia(CH).We provisionally designated it as cochlear hypoplasia type X(CH-X).Conclusion Cochlear hypoplasia(CH-X),characterized by cochlea with less than 0.5 turns,represents a severe type of inner ear malformation,accounting for approximately 2％of such deformities.Due to the malformed cochlea lacking a distinct bony cochlear nerve canal(BC-NC)and cochlear nerve(CN),the potential benefits of cochlear implant surgery may be relatively limited.
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