Disclaimer: The information contained within the Grand Rounds Archive is intended for use by doctors and other health care professionals. These documents were prepared by resident physicians for presentation and discussion at a conference held at Baylor College of Medicine in Houston, Texas. No guarantees are made with respect to accuracy or timeliness of this material. This material should not be used as a basis for treatment decisions, and is not a substitute for professional consultation and/or peer-reviewed medical literature. Congenital Inner Ear Malformations The reported incidence of significant sensorineural hearing loss in young children varies from 1:1000 to 1:2000 depending on the population studies. Approximately 20% of patients with congenital sensorineural hearing loss have radiographic anomalies of the inner ear. The structure of the inner ear consists of a membranous labyrinth surrounded by a bony labyrinth within the petrous temporal bone. The primordium of the membranous labyrinth, which is referred to as the otic placodes, appears in the third week of gestation as thickened planes of surface ectoderm on either side of the developing hindbrain. It differentiates into the otic pit and then fuses to become the otic vesicles, or otocyst, by the fifth week. The otocyst subdivides into two pouches. The ventral portion develops into the cochlear duct and saccule. The dorsal segment is transformed into the endolymphatic sac and duct, utricle, and semicircular canals. By the 10th week, the adult membranous labyrinth is recognized, and completely developed by week 26. The bony semicircular canals began at the sixth week and are complete by week 22. The superior semicircular canals are completed first, followed by the posterior and finally the lateral. The bony labyrinthine begins in the fourth week as a condensation of mesenchyme and forms a cartilage capsule around the developing membranous labyrinth. Its ossification begins at week 14 and is completed by week 23. Congenital ear malformation results from a defect in the development of the membranous labyrinthine, the osseous labyrinthine, or both. The malformations limiting the membranous labyrinthine cannot be detected radiographically. Complete labyrinthine dysplasia is very rare, and was first described by Bing and Siebenmann in 1907. It has been associated with Jervell-Lange Nielson and Usher's syndromes. Cochleosaccular dysplasia was first described by Schiebe in 1892. It is characterized by a collapse of the cochlear duct and saccule. It is probably the most common form of inner ear pathology in patients with congenital deafness. The Alexander's ear deformity, or the cochlear base turn dysplasia, is related to familial high frequency sensorineural hearing loss. Jackler has classified cochlear anomalies based on inner ear embryogenesis. The complete labyrinthine aplasia, known as Michel's deformity, represents an early failure in development correlating to the third week of gestation. It is extremely rare. The common cavity deformity represents developmental arrest at the fourth week, and a common cavity of the cochlea and vestibule is formed with internal architecture. Cochlear aplasia results from the arrested development of the cochlea during the fifth week. The cochlea fails to form and appears as a single cavity. The vestibule and semicircular canals may be normal or malformed. Cochlear hypoplasia displays a small, rudimentary cochlea but is associated with a normal or malformed vestibule and semicircular canals. This lesion is due to an arrest at the sixth week of gestation. Incomplete partition deformity, also well known as Mondini's deformity, represents a small cochlea with incomplete or no intrascalar septa. The cochlea is usually flat and has one and one-half turns instead of the normal two and one-half turns. Arrest of maturation at the gestational seventh week may result in the Mondini deformity. The internal auditory canal (IAC) may be enlarged or stenosed. The narrow IAC can be associated with a failure of the 8th nerve development. Patients with the wide IAC may be predisposed to cerebral spinal fluid (CSF) leaks, resulting in recurrent meningitis. Patients with the Mondini deformity and other congenital inner ear malformations are at an increased risk for developing recurrent meningitis or perilymphatic fistula. They are predisposed to develop a CSF leak due to the enlarged cochlear aqueduct or an abnormal connection between the internal auditory canal and the membranous labyrinth. A thorough clinical, audiological and radiological evaluation should be made of all patients suspected of having these deformities. Clinical history should include possible exposure to teratogen during pregnancy, family history of hearing impairment, progression and/fluctuation of the hearing loss, and associated vestibular symptom. A routine audiologic evaluation is required. Work-ups can be helpful in determining possible etiology. These include TORCH titers, FTA-ABS, urinalysis, and thyroid function tests. High resolution, computed tomography provides excellent visualization of the bony labyrinthine of the inner ear. Patients are advised to avoid contact sports because of the increased risk of CSF leak following minor head injury. Middle ear infections are treated aggressively because of the increased risk for meningitis. Genetic counseling is provided after a careful analysis of the family history. Hearing rehabilitation, including amplification and especially educational efforts, are also indicated. Currently, cochlear implantation is indicated for bilaterally profound sensorineural hearing loss without speech discrimination using hearing aids. It is contraindicated in the patient with complete cochlear aplasia and narrow IAC since neural elements for stimulation would be absent. Further study is required to evaluate the long-term benefits of cochlear implantation in the congenital inner malformation. Case Presentation A patient was referred to Texas Children's Hospital at eight months of age with a history of developmental delay and no perception to auditory stimuli. She was a term infant, weighing 7 lbs 11 oz when delivered by Caesarean section due to breech presentation. Her postnatal care was uncomplicated. The pregnancy was only complicated by a urinary tract infection and hypertension during the third trimester. She was recently diagnosed with congenital hypotonia, but was otherwise healthy without any previous ear problems. An ABR demonstrated no response to air or bone conduction click stimuli. Her family history was only significant for a maternal grandmother with a hearing loss. Physical examination was unremarkable. Titers were negative for cytomegalovirus, rubella, toxoplasma, and herpes simples virus. Thyroid function tests were within normal limits. A high resolution temporal bone CT scan revealed cochlear common cavity deformity. She was fitted with bilateral behind-the-ear (BTE) hearing aids. Repeat audiogram demonstrated her aided speech detection threshold to be 60 dB, and a 1000 Hz warble tone at 70 dB. She has been involved in a total communication program. Her parents noted significant differences in her sound perception with hearing aids. Currently she has been using a five-word vocabulary. Bibliography Brookhouser PE. Sensorineural hearing loss in children. In: Cummings CW, Harker LA, editors. Otolaryngology - Head and Neck Surgery, 2nd ed. St. Louis: Mosby, 1993:3080-3102. 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Laryngoscope 1987;97(Suppl):15-17. Johnsson L-G, Hawkins JE Jr, Rouse RC, Kingsley TC. Four variations of the Mondini inner ear malformations as seen in microdissections. Am J Otolaryngol 1984;5:242-257. Jorgensen MB, Kristensen HK, Buch NH. Thalidomide-induced aplasia of the inner ear. J Laryngol Otol 1964;78:1095-1101. Lindsay JR. Profound childhood deafness: inner ear pathology. Ann Otol Rhinol Laryngol 1973;82(Suppl 5):1-73. Makishima K, Snow JB Jr. Pathologic features of the inner ear in congenital deafness. Arch Otolaryngol 1975;101;600-604. Mangabeira-Alberrnaz PL. The Mondini dysplasia - from early diagnosis to cochlear implant. Acta Otolaryngol 1983;95:627-631. Mangabeira-Albernaz PL, Fukuka Y, Chammas F, Ganança MM. The Mondini dysplasia - a clinical study. ORL J Otorhinolaryngol Relat Spec 1981;43:131-152. Mitchell DP, Rubin AM. Mondini dysplasia - late complications. J Otolaryngol 1985;265-267. Miyamoto RT, McConkey Robbins AJ, Myres WA, Pope ML. Cochlear implantation in the Mondini inner ear malformation. Am J Otol 1986;7:258-261. Molter DW, Pate BR Jr, McElvenn JT Jr. Cochlear implantation in the congenitally malformed ear. Otolaryngol Head Neck Surg 1993;108:174-177. Murakami Y, Schuknecht HF. Unusual congenital anomalies of the inner ear. Arch Otolaryngol 1968;87:335-349. Nadol JB Jr. Histological considerations in implant patients. Arch Otolaryngol 1984;110:160-163. Nadol JB Jr, Young Y-S, Glynn RJ. Survival of spiral ganglion cells in profound sensorineural hearing loss: implications for cochlear implantation. Ann Otol Rhinol Laryngol 1989;98:411-416. Ohlms LA, Edwards MS, Mason EO, Igarashi M, Alford BR, Smith RJH. Recurrent meningitis and Mondini dysplasia. Arch Otolaryngol Head Neck Surg 1990;116:608-612. Otte J, Schuknecht HF, Kerr AG. Ganglion cell populations in normal and pathological human cochleae: implications for cochlear implantation. Laryngoscope 1978;88:1231-1246. Paparella MM. Mondini's deafness: a review of histopathology. Ann Otol Rhinol Laryngol 1980;89(Suppl 65):1-23. Phelps PD. Cochlear implants for congenital deformities. J Laryngol Otol 1992;106:967-970. Phelps PD. Congenital lesions of the inner ear, demonstrated by tomography: a retrospective study of 34 cases with special reference to the lateral semicircular canal. Arch Otolaryngol 1974;100:11-18. Reilly JS. Congenital perilymphatic fistula: a prospective study in infants and children. Laryngoscope 1989;99:393-397. Sando I, Takahara T, Ogawa A. Congenital anomalies of the inner ear. Ann Otol Rhinol Laryngol 1984;93:(Suppl 112):110-118. Schmidt JM. Cochlear neuronal populations in developmental defects of the inner ear. Acta Otolaryngol 1985;99:14-20. Schuknecht HF. Mondini dysplasia: a clinical and pathological study. Ann Otol Rhinol Laryngol 1980;89:3-23. Shelton C, Luxford WM, Tonokawa LL, Lo WW, House WF. The narrow internal auditory canal in children: a contraindication to cochlear implants. Otolaryngol Head Neck Surg 1989;100:227. Suehiro S, Sando I. Congenital anomalies of the inner ear: introducing a new classification of labyrinthine anomalies. Ann Otol Rhinol Laryngol 1979;88:2-24. Supance JS, Bluestone CD. Perilymph fistulas in infants and children. Otolaryngol Head Neck Surg 1983;91:663-671. Swartz JD, Harnsberger HR. Imaging of the Temporal Bone, 2nd ed. NY: Thieme, 1992;192-246. Tom LW, Bilaniuk L, Roa RA, Potsic WP. Recurrent meningitis and a congenital perilymph fistula. Ear Nose Throat J 1992;71:287-290. Tsuzuki T, Kaga K. The relation between motor function development and vestibular function tests in four children with inner ear anomaly. Acta Otolaryngol 1991;481:443-446. Wetmore SJ, Herrmann P, Fisch U. Spontaneous cerebrospinal fluid otorrhea. Am J Otol 1987;8:96-102. Zalzal GH, Shott SR, Towbin R, Cotton RT. Value of CT scan in the diagnosis of temporal diseases in children. Laryngoscope 1986;96:27-32. 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