Plain language summary

Here, we describe two congenitally deaf male siblings with the same compound heterozygotic, likely pathogenic mutations in the FGF3 gene, associated with the labyrinthine aplasia, microtia and microdontia (LAMM) syndrome. Both children had bilateral cochleovestibular aplasia, precluding cochlear implantation. The elder brother received an auditory brainstem implant (ABI) with very limited auditory responses. During the ABI-surgery of the younger subject, it was discovered that excellent auditory responses could be obtained when the electrode array was placed considerably more caudally and more medially than standard. It was observed that the foramen of Luschka, the entrance to the lateral recess of the fourth ventricle was located more caudally. In view of this observation the good auditory development of the latter child, it was decided to give the older child a contralateral ABI. Again, it turned out that the anatomy of the brainstem was abnormal with a more caudal location of the foramen of Luschka and the cochlear nucleus, and this child is showing good progress with his auditory development. It is concluded that one should be aware of the anatomical differences at the level of the brainstem when placing an ABI in children with this genetic disorder (and most likely also in the LAMM syndrome). This also underpins the need of a multidisciplinary approach with closely collaborating team members and good family guidance when diagnosing and treating children with rare deafness.

Deviant surgical anatomy for auditory brainstem implants with FGF3 gene defects, associated with LAMM syndrome

This case series describes three placements of Auditory Brainstem Implants (ABIs) in two congenitally deaf brothers with a gene defect associated with the Labyrinthine Aplasia, Microtia and Microdontia (LAMM) syndrome. In line with this syndrome, they both had no inner ears and no hearing nerves and therefore couldn’t be helped with a cochlear implant. The only option was an ABI, with a mesh electrode positioned on the cochlear nucleus, the first relay station of the hearing system in the brainstem. The first ABI electrode in the elder brother was placed in the classical position and did not yield much benefit. During the ABI surgery in the younger sibling, it was discovered that the location of the cochlear nucleus (the target site for an ABI) was located further down and the electrode had to be inserted deeper. This child showed a good auditory development, and it was decided to give the older child an ABI at the other side. Again, it turned out that the anatomy of the brainstem was abnormal with a lower location of the cochlear nucleus. With this second implant, this child’s auditory development is showing good progress. It is concluded that one should be aware of the anatomical differences at the level of the brainstem when placing an ABI in children with this genetic disorder (and most likely also in the LAMM syndrome).

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Neuroanatomical anomalies due to a defect in the FGF3 gene,associated with the Labyrinthine Aplasia,Microtia and Microdontia syndrome: insights from the placement of auditory brainstem implants in two siblings