EXTERNAL EAR
AURICLE
Auricular malformations (microtia) can affect the size, shape, position, and orientation of the pinna. Complete absence may also occur, and it is called anotia. Anterior to the auricle, ear appendages, ear sinus, and ear pits may also be found [4]. Weerda's classification is the most accepted and commonly used for microtia at the present time [5].
EAC
Failures in the canalization result in EAC malformations, stenotic or even absent canal. It can affect the fibrous canal, bony, or both. It must be suspected with auricular anomalies or narrow external meatus (less than 4 mm) [6].
MIDDLE EAR
Isolated anomalies of the middle ear structures without the involvement of external ear malformations are less common than combined ones. Altmann´s classification differentiates three combined malformations of the external and middle ear, called congenital aural atresia [7]:
OSSICLES
There is a wide spectrum of ossicular chain malformations. The ossicles may present with any kind of dysplasia, decreased size, abnormal rotation, displacement, fusion, or even absence. The most common abnormalities are fixation of the malleus and/or incus, incudostapedial discontinuity, and stapes fixation [6,8].
FACIAL NERVE
The most common facial nerve anomaly when other middle ear malformations are present is the displacement of the tympanic segment [8]. The nerve is usually displaced medially and inferiorly crossing the oval window inferiorly.
TYMPANIC CAVITY
The tympanic cavity may be hypoplastic or completely aplastic. An extra misplaced cavity can occur, and it is called extracavitation.
MASTOID PNEUMATIZATION
Mastoid pneumatization is very variable. It may be increased or severely reduced/absent.
VASCULAR ANOMALIES
- Aberrant internal carotid artery: results from the regression of the cervical portion during development [9]. It courses posterior to the normal path of the original artery, entering the tympanic cavity through an enlarged inferior tympanic canaliculus.
- Persistent stapedial artery: usually associated with aberrant ICA.
- Jugular bulb variations: the most common is a high-riding jugular bulb.
INNER EAR
COMPLETE LABYRINTHINE APLASIA (also called Michel deformity)
The complete absence of the inner ear structures (cochlea, vestibule, semicircular canal, vestibular and cochlear aqueducts) due to an arrest during a very early stage in pregnancy, before the otic placode, has completely developed [10]. Usually, the petrous bone may be hypoplastic and the internal auditory canal may be affected.
There are three subgroups of CLA:
- CLA with hypoplastic or aplastic petrous bone.
-CLA without otic capsule.
- CLA with otic capsule.
COCHLEAR APLASIA
The complete absence of the cochlea. The other elements of the inner ear may develop normally or may be malformed [10,11].
There are two subgroups according to the accompanying vestibular system:
- Cochlear aplasia with a normal labyrinth
- Cochlear aplasia with a dilated vestibule
COMMON CAVITY
The common cavity is the result of the failure of the vestibule and cochlear differentiation [10]. It consists of a single ovoid structure or cystic cavity with no defined internal architecture. It is frequently seen that its shape is wider than it is tall. The SCC can be normal or rudimentary. The IAC usually opens at the central part of this cavity.
COCHLEAR HIPOPLASIA
Cochlear and vestibule are well-differentiated but the cochlea is smaller, and it may have internal deformities. There are four subtypes [10-12]:
INCOMPLETE PARTITIONS
Group of anomalies with correct differentiation of the cochlea and vestibule and normal external dimensions but with internal architecture defects. There are three different subtypes according to the defect in the modiolus and the interscalar septa [10-13].
VESTIBULE AND SEMICIRCULAR CANALS (SCC)
The malformed canals are usually short and wide, with a small bony island, and the vestibule may appear dilated. The malformation of the lateral SCC is one of the most common inner ear anomalies, and the most frequent of the three canals as is the last to develop [6,10].
INTERNAL AUDITORY CANAL (IAC)
An abnormal or stenotic IAC (<2mm) could suggest an underlying hypoplastic or absent cochlear nerve [13,14]. MRI must be performed to assess this involvement.
ENLARGED VESTIBULAR AQUEDUCT (EVA)
EVA is the most common radiological abnormality in early sensorineural hearing loss onset and is bilateral in >90%. Different criteria have been described to determining the exact measurements for an EVA. Some use an axial measurement between common crus and external aperture >1mm (or when the diameter exceeds that of the posterior SCC) [13,14].