Imaging description

The spectrum of congenital cochlear and vestibular anomalies is very wide, ranging from complete absence of the inner ear structures to minimal dysplastic chances that are difficult to visualize. Essentially all of these present with bilateral congenital sensorineural hearing loss, however [1].

The most severe variety is known as labyrinthine aplasia (Michel’s anomaly), where there is no cochlea, vestibule, or semicircular canal development at all. Common cavity is lesser in severity and refers to a single “cystic” space that represents a combination of dysplastic vestibule and cochlea that does not closely resemble either [2]. When the developmental arrest occurs around week 7 of gestation the cochlea is better formed and may present as incomplete partition type I (IP-I) (Fig. 61.1), where there is incomplete development of all turns of the cochlea, with lack of modiolus. When there is normal differentiation of the basilar turn of the cochlea with incomplete partition between middle and apical cochlear turns and a large vestibular aqueduct (LVA), it is known as incomplete partition type II (IP-II) anomaly (Figs. 61.2, 61.3). This is also known as the classic Mondini type of anomaly, although in the literature the term Mondini is commonly used, erroneously, to refer to a wide spectrum of inner ear anomalies [3]. An even milder form of cochlear dysplasia is due to incomplete development of the apical turn of the cochlea, which occurs at week 8 of gestation (Fig. 61.4). It results in modiolus deficiency with mild asymmetry of the scalar vestibuli and scala tympani. It is often associated with LVA.