Development of the stapedius muscle canal and its possible clinical consequences

To study the development of the stapedius muscle canal in human embryos and foetuses.

46 temporal bones with ages between 9mm and new-borns were studied. The preparations were dyed using Martins' trichrome technique.

Two areas of different embryological origin form the stapedius muscle canal, which contains this muscle and the facial nerve. On the otic capsule, at 11 weeks an extension starts to grow from its caudal part, which moves outwards and near to Reichert's cartilage, forming the footplate and internal wall. The pyramidal eminence comes from the mesenchyme that surrounds the muscle, forming a partition to separate it from the laterohyale portion of Reichert's cartilage. Extensive connections are observed in its development between bone marrow and mesenchyme. At 35 weeks the muscle and nerve start to separate by means of a bony partition. If this partition does not form, there is going to be a dehiscence that could cause peripheral nerve pathology due to the repeated contraction of the muscle, or the dissemination of infections from middle ear.

During the development of the stapedius muscle canal the presence of dehiscences between the facial nerve and the muscle may have clinical repercussions.