Mondini malformation

Mondini malformation is a historical term used to described incomplete partition type II anomaly with large vestibular aqueduct.

The term is often used inappropriately to describe any cochlear abnormality, rather than a specific type of cochlear hypoplasia. Thus, most would favour not using the term, except perhaps in cases where the findings exactly match those described by Mondini.

Clinical presentation

Patients have sensorineural hearing loss, which is usually bilateral as the basal turn of the cochlea is intact, high-frequency hearing is generally preserved.

Pathology

The abnormality is thought to result from a relatively late insult during the 7^th week of embryological development when most of the inner ear has already formed. Earlier insults result in more severe abnormalities (Michel deformity, cochlear aplasia and cochlear hypoplasia).

See classification of congenital cochlear anomalies.

There are only 1.5 turns to the cochlea instead of the expected 2.5. The interscalar septum between the middle and apical segments also fails to form leading to a confluent, sac-like cochlea

Associations

Mondini dysplasia has been associated with thalidomide and rubella embryopathies as well as a number of syndromes:

• Pendred syndrome: bilateral sensorineural hearing loss and goitre ^3,5
• CHARGE syndrome ⁴
• Klippel-Feil syndrome ⁵
• DiGeorge syndrome ⁵
• Wildervanck syndrome ⁵

Some publications have suggested a link between Mondini malformation and spontaneous CSF fistulae and meningitis; however, this appears to be only the case with more severe forms of cochlear hypoplasia, and not with a true isolated Mondini malformation ^1,4.

Radiographic features

The Mondini abnormality consists a triad ¹:

1. abnormal cochlea
   • only 1.5 turns (instead of the normal 2.5 turns)
   • normal basal turn with a cystic apex in place of the distal 1.5 turns
2. enlarged vestibule with normal semicircular canals
3. enlarged vestibular aqueduct containing a dilated endolymphatic sac

Additionally, complete or partial absence of the normal interscalar septum is also present, which can now be demonstrated on high-resolution MRI ⁴.

Treatment and prognosis

Hearing can be improved by implantation of multichannel cochlear implant ⁶.

Complications

There is an increased risk of:

• meningitis
• perilymphatic fistula

History and etymology

It was first described in Latin by Carlo Mondini: Italian anatomist (1729-1803) in 1791 ^1-2.