Familial lateral semicircular canal malformation with external and middle ear abnormalities

Abstract

We report a family with inner ear lateral semicircular canal (LSC) malformation and external and middle ear abnormalities. The family had no history of known syndromes or toxic exposures. Distinct phenotypic manifestations were found in three family members. A young girl exhibited bilateral LSC malformation with a right-sided preauricular tag, a mildly deformed auricle, a stenotic external auditory canal, and a constricted middle ear cavity. She had moderate conductive hearing loss in the right ear but normal hearing in the left ear. Her younger brother exhibited right-sided LSC malformation, microtia, external auditory canal atresia, a malformed middle ear cavity, and abnormal auditory ossicles. He had severe mixed hearing loss in his right ear. Their mother exhibited left-sided LSC malformation without external and middle ear abnormalities, and the hearing was normal in her left ear. None of the three cases had vestibular symptoms, and their results of balance tests were appropriate for the corresponding ages. In contrast, significantly decreased LSC function was revealed by caloric tests in an ear with LSC malformation. Previously, LSC malformation may have been underdiagnosed in patients presenting with external and middle ear abnormalities and their relatives, since this malformation is frequently associated with normal hearing and balance or conductive hearing loss only. To our knowledge, this condition has not been described previously. This condition supports a genetic basis for the combination of LSC malformation and external and middle ear abnormalities and may represent an autosomal dominant condition with variable expressivity. KEY WORDS: lateral semicircular canal malformation; external ear malformation; middle ear malformation; hearing loss; autosomal dominant inheritance INTRODUCTIONDevelopmental defects of the first and second branchial arches and the first branchial cleft lead to malformations of the external ear, such as microtia characterized by underdeveloped auricles, stenosis or atresia of the external auditory canal, and preauricular pits, fistulas, and tags [Melnick et al., 1979;Moore and Persaud, 1998]. The prevalence of microtia in different populations ranges from 0.4 to 5.5 per 10,000 births [Allanson, 1995;Mastroiacovo et al., 1995;Calzolari et al., 1999]. This anomaly is most commonly associated with stenosis or atresia of the external auditory canal [Jafek et al., 1975;Kountakis et al., 1995]. Because the external and middle ears share a common embryological origin, concomitant malformation of these structures is also common [Jafek et al., 1975;Swartz and Faerber, 1985;Kountakis et al., 1995;Mayer et al., 1997]. In contrast, malformation of the inner ear is much less frequently associated with external and middle ear abnormalities [Jafek et al., 1975;Mayer et al., 1997], since the inner ear has an independent embryological origin and develops during different gestational period. Among previously described inner ear malformations associated with external and middle ear abnormalities,...

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