Postnatal change on the location of Ostmann's fatty tissue in the region lateral to Eustachian tube

Objective: To delineate a possible role of protective function by Ostmann's fatty tissue (OF) in the lateral region to Eustachian tube (ET). Study design: Morphometric and histopathological examination on human temporal bones. Methods: OF in the region lateral to the cartilaginous portion of the ET between the ET lumen and the tensor veli palatini muscle (TVP) was studied histopathologically and morphometrically by analyzing a series of vertically cut histologic sections for the ET structures. Sections were obtained from 25 individuals with age ranging from 33 gestational weeks to 38 years at the time of their death. Results: In fetus and neonates, the region lateral to ET was filled with mesenchyme. OF appeared first in this region at 2-3 weeks postnatally, and increased in volume with development of the ET. In the cases of older children and adults (Group-B), the ratio of the volume of OF in the region to that of ET lumen (OF/L) was significantly higher in the posterior half than in the anterior half of the cartilaginous portion of ET. However, in the cases of infants and younger children (Group-A), there was no significant difference in the ratio between the two regions. In the posterior half of the cartilaginous portion of ET, OF/L was significantly higher in Group-B than in Group-A, while in the anterior half, there was no significant difference in the ratio between two age groups (Group-A and B). Conclusions: In Group-B, the dominant OF in the area of the posterior half of the cartilaginous region, which includes the narrowest portion of ET, may be responsible for restorating the ET lumen back to its closed static condition after active tubal opening by contraction of TVP. This is thought to be important for protection of the middle ear. On the other hand, in Group-A, poor OF near the narrowest portion of ET may cause insufficient restoration of the ET lumen and increased risk of developing otitis media (OM).