Histopathologic study of congenital aural atresia in the human embryo

We studied the histopathologic features of the temporal bones in a human embryo with unilateral aural atresia. The developmental stage of the embryo was at stage 22 in the Carnegie system, and the estimated ovulation age was 8 weeks. There were severe hypoplastic changes in Meckel's and Reichert's arch cartilages without differentiation of the auditory ossicles, hypoplasia of the tubotympanic recess, and resultant abnormal passing of the facial nerve in the affected ear. Abnormal lateral extension of the cartilaginous otic capsule replaced a posterior half of the middle ear region and seemed to form the so-called atresia plate. The external and middle ears of the unaffected side and the bilateral inner ears were morphologically normal. These findings might explain some parts of the complicated mechanism in the development of middle ear anomalies encountered in surgery for congenital aural atresia.