Anatomical feature of the middle cranial fossa in fetal periods: possible etiology of superior canal dehiscence syndrome.

Conclusion: Different from adults, the superior semicircular canal (SSC) protrudes into the cranium during the fetal period. This might cause adhesion of the membranous labyrinth to dura as the bony labyrinth develops much later than the membranous labyrinth. This adhesion interferes with ossification and leads to a bony defect in the SSC.

Objectives: The purpose of this study was to investigate a possible etiology of superior canal dehiscence syndrome (SCDS) from a view point of ontogeny.

Methods: Forty-two adult cadavers and 4 fetal cadavers were used for macroscopic observation of the middle cranial fossa (MCF). In addition, six fetuses underwent computed tomography (CT) examinations. The volume data of the CT obtained from four adults were also used for comparison. Using these CT data, we investigated the anatomic relationship between the MCF and SSC.

Results: The SSC and the cochlea in fetuses protruded into the cranium in macroscopic anatomy and CT examination. On the other hand, the SSC of all adults was completely or mostly buried in the temporal bone.