Measurements of cochlear dimensions in cochlear hypoplasia using temporal bone computerized tomography and temporal magnetic resonance imaging and effects of cochlear implant selection

Inner ear bone anomalies constitute approximately 20% of congenital sensorineural hearing loss. Today, Sennaroglu classification is widely used to evaluate inner ear anomalies. According to this classification, cochlear hypoplasia (CH) is anomalies in which the cochlea and vestibule are selected separately but the cochlea is small in size. There are 4 subtypes, CH I, II, III and IV. The present classification is made according to the radiological image of the cochlea and does not contain an objective measurement. In this study, it was aimed to obtain objective values of hypoplastic cochlea by measuring the dimensions of healthy and hypoplastic cochleas. Thirty-six patients with cochlear hypoplasia according to temporal bone computed tomography (CT) findings and forty normal cochleas with temporal CT due to chronic otitis were included in the study. Using temporal CT, basal turn length, basal turn height and midmodiolar cochlear height were measured axial section through round window Using the 3D MPR (multiplanar reconstruction), the cochlear canal mid-scalar and lateral wall length were marked from the round window to the helicotrema, were measured. Using temporal bone Magnetic Resonance Imaging, the presence of cochlear nerve, vestibular structures and semicircular canals were investigated. According to this, there was a significant difference in basal turn length, basal turn height, midmodiolar height, cochlear canal mid-scalar and lateral wall length between control groups and CH I, II and III (p <0.001). The basal turn height and the cochlear canal lateral wall length in CH IV were significantly lower when compared with the control group (p <0.001 and p = 0.002, respectively). Cochlear hypoplasia should be suspected axial section through round window in the temporal CT is less than 7.5 mm in the basal turn length and 3.5 mm in the midmodiolar height. These two measurements can easily be done by clinicians. Once hypoplastic cochlea is diagnosed, subtyping should be performed and appropriate cochlear implant should be selected according to the type of cochlear hypoplasia. While there is not enough benefit from selecting a short electrode according to the size of the cochlea, long electrodes also increase apical damage. It is believed that this study is a guide to the clinicians in choosing the electrode to cochlear hypoplasia subtype.