Case of the Week
Section Editors: Matylda Machnowska1 and Anvita Pauranik2
1University of Toronto, Toronto, Ontario, Canada
2BC Children's Hospital, University of British Columbia, Vancouver, British Columbia, Canada
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June 30, 2016
Complete Labyrinthine Aplasia (CLA)
- Background:
- Michel aplasia, also known as complete labyrinthine aplasia, is a rare congenital inner ear abnormality accounting for approximately 1% of cochlear bony malformations.
- This condition is defined as complete absence of inner ear structures and is caused by developmental arrest of the otic placode early during the third week of gestation.
- Clinical Presentation:
- Congenital sensorineural hearing loss (SNHL)
- Key Diagnostic Features:
- Petrous apex hypoplasia
- Internal auditory canal hypoplasia
- Hypoplastic stapes
- Absence of inner ear structures (absence of cochlea, vestibule, SCC, vestibular aqueduct, round and oval windows)
- Absence of vestibular and cochlear nerve and aberrant course of facial nerve canal
- It is associated with abnormalities of the skull base (platybasia) and the craniocervical junction; vascular abnormalities, such as abnormal transverse sinus and jugular veins; and abnormalities of the posterior fossa (arachnoid cysts).
- There are different degrees of hypoplasia of the middle ear and mastoid, though associated anomalies of middle and external ear are uncommon because of their different embryologic origin.
- Areas of sclerotic bone can be observed in the temporal bone (may mimic labyrinthitis ossificans).
- Differential Diagnoses:
- Cochlear aplasia: Failure of cochlea development late in the third week of gestation. The vestibule and semicircular canals are either normal, dilated, or hypoplastic.
- Common cavity: Developmental arrest occurs at the fourth week of gestation, resulting in a cystic space formed by a rudimentary cochlea and vestibule. The semicircular canals may be normal or dysplastic. The internal auditory canal can be wide or narrow.
- Cochlear hypoplasia: The cochlea and vestibule can be differentiated from each other, but the size of the cochlea is smaller than normal. Developmental arrest occurs at the sixth week of gestation.
- Incomplete partition I: It is also known as cystic cochleovestibular malformation, where the cochlea has no bony modiolus, resulting in an empty cystic cochlea. This is accompanied by a dilated cystic vestibule with developmental arrest at the fifth week of gestation.
- Incomplete partition II: The cochlea consists of 1.5 turns; the apical and middle cochlea turns are undifferentiated and form a cystic apex. The vestibule is normal, while the vestibular aqueduct is almost always enlarged. Developmental arrest occurs at the seventh week of gestation.
- Labyrinthine ossificans: Most commonly bilateral and is affected in child weeks to months after acute meningitis episode. It shows high-density bone deposition within membranous labyrinth, promontory well-formed (flat in labyrinthine aplasia).
- Treatment:
- Cochlear implant is not possible in these patients due to the lack of inner ear structures and absent cochlear nerve. Therefore, the treatment of choice is auditory brainstem implant (ABI).
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