Mondini malformation

Findings

Non-contrast axial CT images through the temporal bones demonstrate incomplete partitioning of the left cochlea and nonvisualization of the modiolus resulting in confluency between the middle and apical segments. Compare this to the right cochlea, which is normal. There is also abnormal dilitation of the left vestibular aqueduct.


Diagnosis: Mondini malformation


Case points

Mondini malformation occurs when there is abnormal development of the cochlea resulting in less than 2.5 turns and incomplete formation of the modiolus.
It is a cause of sensorineural hearing loss.


Discussion

Mondini malformation refers to an anomaly of the cochlea in which the modiolus fails to develop properly in the seventh week of fetal life, resulting in a cochlea with only 1.5 turns instead of the normal 2.5 turns. In addition, the interscalar septum between the middle and apical segments fails to form leading to a confluent, sac-like cochlea. There is an association with an enlarged vestibular aqueduct and anomalies of the vestibules and semicircular canals. In some cases, Mondini malformation may also be associated with Pendred Syndrome (bilateral sensorineural hearing loss and goiter)

Patients present with gradual or sudden sensorineural hearing loss with preservation of high-frequency hearing because the basal turn of the cochlea is usually preserved. These patients are also at increased risk for developing meningitis or perilymphatic fistula.

Treatment revolves around clinical presentation. Cochlear implants may be used to enhance hearing while middle ear infections are treated aggressively due to the increased risk for meningitis.