Microfissure between the round window niche and posterior canal ampulla.

The microfissure between the round window niche and the posterior canal ampulla was examined in fetal, child, and adult human temporal bones. The communication which was filled with mesenchymal tissue and blood vessels extending from the middle ear, was observed between the round window niche and the posterior canal ampulla in 10 to 15-week human fetuses. The mesenchymal tissue in the communication was replaced by cartilage with advancing age of the fetus. No communication was observed at birth. From newborn to 12 months of age, no microfissure was observed. After one year of age, the microfissure was first observed and the frequency of the observation increased with increasing age of the patient. After six years of age, the microfissure was observed bilaterally in 100% of cases studied. The microfissure has its origin from the communication between the round window niche and the posterior canal ampulla in fetal life, and is a normal developmental and anatomical structure, and not a pathological finding.