Mesenchyme Remaining in Human Temporal Bones

This study was conducted in order to gain basic information about mesenchyme remaining in the middle ear cleft in normal infants. Because no previous report has objectively described the quantity or quality of such postnatal remnants in normal infants, it has not been possible to accurately evaluate the significance of mesenchyme remaining in the middle ears of infants with pathologic conditions, such as otitis media and congenital anomalies. Thus, 53 temporal bones obtained from 41 individuals reported upon here—from 26 weeks' gestation to 8 years of age—will be controls for future studies of pathologic conditions. The children from whom these temporal bones were obtained had no anomalies of the ear (or any other known part of the body); nor did they have any pathologic conditions in the ear. The temporal bones were prepared for histologic study with hematoxylin and eosin staining and were examined under the light microscope. After areas of the mesenchyme in the histologic sections were projected and illustrated for each of 19 portions in the middle ear cleft under the microprojector, those areas were measured by compensating polar planimetry. The findings obtained in this study were as follows: (1) The amount of mesenchyme remaining in the days after birth seemed to gradually decrease in volume with increased maturity and had nearly disappeared within the first year in normal infants. Where mesenchyme was noted in the temporal bones of infants over 1 year of age, it was usually present only in small niches. (2) Most mesenchyme found in temporal bones of normal infants was seen in the mastoid antrum; it was also found in the aditus ad antrum, the epitympanum, the hypotympanum, the sinus tympani, the round window niche, the oval window niche, and the mesotympanum.