The shortened cochlea: its classification and histopathologic features

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Abstract

Introduction: The term ‘Mondini dysplasia’ has been used to describe virtually any congenital abnormality of the osseous labyrinth resulting in confusion and seemingly contradictory observations and conclusions about this type of deformity. The purpose of this study is to histopathologically classify and describe temporal bones whose cochleas have less than 2.5 turns. Methods: Of the 1800 temporal bones in our collection, 21 from 12 cases were found to have cochleas with less than 2.5 cochlear turns. Ages ranged from stillborn to 50 years. Temporal bones were harvested at autopsy, processed and embedded in celloidin. Sections were cut at a thickness of 20 μm and every 10th section stained with hematoxylin–eosin and examined using light microscopy. The number of turns, length of cochlea, integrity of cochlear base, length of modiolus, abnormalities of the semicircular canals and vestibule, enlargement of the vestibular aqueduct and middle ears were documented. Twenty-one temporal bones from age-matched patients without cochlear deformities were used as controls for modiolar length measurements. Results: Malformation of the shortened cochlea was histopathologically classified into three groups as follows: (1) Common cavity, cochlear dysplasia (one ear)—severe dysplasia of the cochlea without a complete basal turn; (2) Mondini dysplasia (11 ears)—1.5 cochlear turns, a complete basal turn, an incomplete or absent interscalar septum and a complete bone at the base of the modiolus; and (3) Mondini-like dysplasia type A (five ears)—2 turns to the cochlea including a complete basal turn and complete bone at the base of the modiolus; and type B (four ears)—1.5–2 turns to the cochlea, hypoplasia of or a missing bone at the base of the modiolus (either with or without a communication between the internal auditory canal and the cochlea) and a complete basal turn. Conclusion: The range of congenital malformations in short cochlea is highly variable. Fundamental to the accurate evaluation of a labyrinthine anomaly, malformations of the inner ear should be classified according to the findings in the labyrinth. We suggest the use of common cavity cochlear dysplasia, Mondini dysplasia and Mondini—like dysplasia to describe these variable anomalies.

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.

References (21)

  • C. Mondini, Anatomica hati sectio. De Bononiensi Scientarum et Artium Instituto atque Academia Commentarii, Bononiae...
  • M.M. Paparella

    Mondini Deafness: a review of histopathology

    Ann. Otol. Rhinol. Larygol.

    (1980)
  • H.F. Schuknecht

    Mondini's Dysplasia: a clinical and pathological study

    Ann. Otol. Rhinol. Larygol.

    (1980)
  • J. Jensen

    Malformation of the inner ear in deaf children

    Acta Radiologia

    (1969)
  • J. Jensen

    Congenital anomalies of the inner ear

    Radiol. Clin. North Am.

    (1972)
  • R.K. Jackler et al.

    Congenital malformations of the ear: a classification based on embryogenesis

    Laryngoscope

    (1987)
  • P.D. Phelps

    The basal turn of the cochlea

    Br. J. Radiol.

    (1992)
  • H.F. Schuknecht
  • D.L. Tucci et al.

    Cochlear implantation in patients with cochlear malformations

    Arch. Otolaryngol. Head Neck Surg.

    (1995)
  • P.D. Phelps

    Mondini and ‘Pseudo Mondini’

    Clin. Otolaryngol.

    (1990)
There are more references available in the full text version of this article.

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Presented at the Midwinter Meeting of the Association of Research in Otolaryngology, St. Petersburg Beach, Florida, 2001.

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