CASE 15574 Published on 15.04.2018

Late diagnosis of labyrinthine (Michel) aplasia in a 16-year-old girl with congenital anacusis

Section

Head & neck imaging

Case Type

Clinical Cases

Authors

Kadish Lucien K, Tiona Micheline, Amriss Omar, Moussali Nadia, El Benna Naima

CHU IBN Rochd;
Casablanca, Morocco;
Email:kadishkayij@gmail.com
Patient

16 years, female

Categories
Area of Interest Ear / Nose / Throat ; Imaging Technique CT
Clinical History
A 16-year-old female patient with bilateral congenital hearing impairment was referred to our department of radiology for a temporal bone CT.
Imaging Findings
Fig. 1: Axial and coronal temporal bone CT images showing the normal anatomy of the inner ear.

Fig. 1a: Vestibule recess, vestibular aqueduct, lateral and semicircular canals.

Fig. 1b: Modiolus, cochlea, vestibule recess and posterior semicircular canal.

Fig. 1c: Cochlea and round window.

Fig. 1d: Tympanic and labyrinthine segments of facial nerve canal.

Fig. 1e: Internal acoustic canal, vestibule recess, superior and lateral semicircular canal.

Fig. 2 and Fig. 3 show bilateral absence of vestibule, semicircular canals, cochlea and vestibular aqueducts on a 16-years-old's temporal bone CT.
Discussion
Hearing disorders are the most common impairment of the sensory nervous system. [1] Congenital hearing loss can result from genetic or environmental causes: infection and ototoxic drug exposure. [2]
The inner ear has 2 main parts: a bony labyrinth and a membraneous labyrinth. The bony labyrinth surrounds the membraneous part that contains a fluid called endolymph and two sacs, the utricle and the saccule. The bony labyrinth is composed of the cochlea, vestibule and three semicircular canals: superior, lateral, and posterior.
About 15-20% of patient with deafness have inner ear malformations. [3]

The most severe labyrinthine malformation known is Michel aplasia, a rare condition in which inner ear structures are absent at birth due to abnormal embryological development during the 3rd gestational week. [3, 4]

The role of imaging in the assessment of congenital deafness is crucial because it allows to delineate ear malformations, thus impacting management and prognosis.
High-resolution CT and MRI of the temporal are convenient to explore the inner ear as they can describe his anatomy with fine details. [2, 3, 5]
CT is most suitable for osseous anatomy and malformation evaluation while MRI better visualises the membranous labyrinth and the vestibulocochlear nerve. [3, 5]
CT images are acquired in a single imaging plane with a multi-slice detector scanner: Helical mode; 120 kV; 250 mAs; Pitch 0.5 mm.
The raw data from each ear are reconstructed separately into 0.6 mm axial images in bone algorithm that effectively magnifies the images.
The coronal set is reconstructed perpendicular to the axial set of images.

According to Jackler and later to Sennaroglu and Saatci, inner ear malformations are classified in terms of both the earliest stage of embryological development arrest and descending order of severity: 1. Michel (labyrinthine) aplasia; 2. Cochlear aplasia; 3. Common cavity; 4. Incomplete partition type I; 5. Cochlear hypoplasia and 6. Incomplete partition type II (Mondini deformity). [3, 6, 7]

Cochlear implantation is indicated in minor malformations such as cochlear hypoplasia. [8]
Auditory brainstem implant is a different approach of auditory rehabilitation that directly stimulates the cochlear nuclear complex in the brainstem.

Michel aplasia is known as complete labyrinthine aplasia. It is defined by bilateral total absence of inner ear structures, resulting in anacusis. This condition represents about 1% of cochlea bony abnormalities.
Imaging has a crucial role in the evaluation of congenital hearing impairment by enabling the diagnosis and characterisation of inner ear malformations with an impact on related prognosis and management.
Differential Diagnosis List
Michel aplasia or complete labyrinthine aplasia.
Cochlear aplasia (hypoplasia)
Other inner ear malformations
Final Diagnosis
Michel aplasia or complete labyrinthine aplasia.
Case information
URL: https://eurorad.org/case/15574
DOI: 10.1594/EURORAD/CASE.15574
ISSN: 1563-4086
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