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KEY POINTS

KEY POINTS

  1. Fetal ears are not routinely evaluated in prenatal anatomical screening.

  2. High-resolution sonography enables assessment of the fetal auditory system by demonstration of the pinnae, external meatus, and tympanic rings.

  3. Imaging of the cochlear labyrinths is possible only in the early second trimester.

  4. Detection of auricular abnormalities can provide useful information for genetic counseling.

  5. An abnormal tympanic ring in a fetus with microtia may indicate congenital aural atresia and an increased risk of postnatal conductive hearing loss.

INTRODUCTION

The ears are an auditory sense organ and play a role in the balance and physical orientation of the body. Abnormal ear development can be associated with dysmorphism, many genetic syndromes, and hearing loss.

The ear has three parts: external, middle, and internal. The external ear is comprised of the auricle and the external acoustic meatus, leading to the tympanic membrane. The middle ear contains the tympanic cavity and three small bones: the malleus, incus, and stapes. The inner ear consists of the cochlea and the semicircular canals. In this chapter each part is discussed separately.

Formation of the human ear is one of the most complex embryonic processes, based on coordinated development of the ectodermal, mesodermal, and endodermal anlages. Such a great complexity may cause a wide variety of structural and functional anomalies. Although the prevalence of permanent bilateral congenital hearing loss is 1.33 per 1000 live births,1 the estimated incidence of ear malformations is approximately 1 in 3800 newborns.2 Malformations of the external ear may present with anotia, abnormalities in the size, shape, orientation, and position of the pinna, and ear tags. A small dysplastic auricle (microtia) is frequently associated with congenital aural atresia (CAA) and anomalous tympanic ring (TR) and middle ear malformations which include abnormal shape and size of the middle ear cavity and the ossicles, and anomalies of the boundary orifices: the TR, the oval, and rarely the round window. Abnormal development of the inner ear results in malformations of the bony and membranous labyrinths, which typically manifest with sensorineural hearing loss (SNHL). Anomalies of the membranous labyrinth and malfunction of the sensory auditory components represent the major cause of the congenital deafness; however, contrary to malformations of the bony labyrinth, they have no imaging features. Radiologically detectable defects of the bony labyrinth (aplasia, hypoplasia, and dysplasia) are responsible for only 20% of congenital SNHL.3

Malformations of the inner ear differ in their embryogenetic mechanisms from those of the outer and middle one. This explains relatively low coincidence (11% to 30%) of inner ear anomalies with outer and middle ones.4

Ear malformations are one of the main features of many syndromes including Treacher-Collins, Goldenhar, Crouzon, Apert, Klippel-Feil, Wildervanck, van der Hoeve-de-Kleyn, Albers-Schönberg, trisomies 13, 18, 21, and 18q syndrome.2 Multiple genes, transcription factors, secretion factors, growth factors, receptors, and cell adhesion ...

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