International Journal of Pediatric Otorhinolaryngology
The shortened cochlea: its classification and histopathologic features☆
Introduction
Congenital malformation of the inner ear is a common cause of congenital sensorineural hearing loss. The malformation may result from arrested development at various stages of fetal life or from abnormal development due to genetic defects. Cochlear malformation may occur in the membranous and/or osseous labyrinth and vary widely in severity. Michel dysplasia is characterized by a complete failure of development of the inner ear; Scheibe and Siebenmann-Bing dysplasias are characterized by malformation of the membranous labyrinth. Mondini dysplasia was originally described as malformation in which the cochlea is shortened to 1.5 cochlear turns with normal semi-circular canals, an enlarged vestibular aqueduct and dilated endolymphatic sac [1]. Since then, the term ‘Mondini’ has been used as an umbrella term in clinical practice to describe almost any type of congenital cochlear deformity. Paparella [2] and Schuknecht [3] reported histopathologic descriptions of a number of cases they called Mondini dysplasia, these included temporal bones with a common cavity and an incomplete interscalar septum of the cochlea.
Jensen [4] recognized Mondini's anomaly on polytomography in 1969. Later, he described a more severe type of deformity that consisted of an amorphous cochlear sac continuous with a dilated vestibule, for which he suggested the term ‘dysplasia’ [5]. Since then, the term ‘Mondini dysplasia’ has come to mean virtually any congenital malformation of the osseous labyrinth, detectable on radiographic examination. In recent years, radiological studies, such as CT and MRI have not only permitted the clinical diagnosis of these disorders, but also the ability to distinguish the different types of cochlear malformations [5], [6]. As confusion still exists as to ‘what is a Mondini and what is not’, we propose a new classification to describe the various types of shortened cochlea.
Although patients with shortened cochlea had been previously considered as poor candidates for cochlear implantation, they now account for an increasing percentage of patients receiving this type of hearing augmentation. Because of the surgical risks that these patients represent, due to anomalies of the inner ear, a concise description of the various types of shortened cochlea is important. In this paper, we present 21 temporal bones from 12 cases with shortened cochlea. Using the original description of Mondini [1] and Phelps's classification [7] (based on radiographic findings of the basal turn of the cochlea) as a guideline, we classify malformations of the cochlea based on histopathologic findings of the temporal bone.
Section snippets
Materials and methods
From the collection the Otopathology Laboratory at the University of Minnesota, Minneapolis, we selected 21 temporal bones from 12 cases with congenital malformation of the bony cochlea. These temporal bones were harvested at the time of autopsy using the bone plug technique, fixed in 10% formalin, defatted in graded series of alcohol, decalcified in 5% trichchloroacetic acid, neutralized with 5% sodium sulfate, dehydrated in graded concentrations of alcohol, and embedded in celloidin.
Results
The age of the patients included in this study ranged from stillborn to 50 years. The malformations varied over a broad range from those with the common cavity type of abnormality to others lacking only the interscalar septum in the second turn of the cochlea. The mean value of modiolar length in temporal bones of controls (Fig. 1) was 2.45 (±0.254) and in temporal bones with cochlear anomalies, 2.045 (±0.518). Mean length of the cochlear ducts in control temporal bones was 32 mm (8) and in
Discussion
Congenital malformation of the inner ear has been reported to occur in approximately, 20% of children with congenital sensorineural hearing impairment [9]. The malformation can result from an arrest of embryogenesis, abnormal development at some stage of fetal life, or genetic defects that may result in distinctive cochlear anomalies entirely different from those found in simple arrests in embryogenesis. Since Mondini first described a case of congenital malformation of the cochlea [1], the
Acknowledgements
This work was supported in part by the International Hearing Foundation; and the Lions International of Minnesota.
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Presented at the Midwinter Meeting of the Association of Research in Otolaryngology, St. Petersburg Beach, Florida, 2001.