Estimated Locations of the Narrowest Portion of the Eustachian Tube Lumen during Closed and Open States

Abstract

To morphologically evaluate the location of the narrowest portion of the eustachian tube (ET) lumen during closed and open states, we used computer-assisted 3-dimensional reconstruction methods to investigate 13 normal human temporal bone–ET specimens obtained from 13 individuals 3 months to 81 years old. On the basis of recent endoscopic observations, we assumed that the site of minimum circumference of the ET lumen represents the site of minimum cross-sectional area during the open state. We tested the hypothesis that the location of the narrowest site of the ET lumen in the closed state is not identical to the site of minimum circumference of the ET lumen. Confirmation of this hypothesis would imply that the site of greatest constriction shifts with contraction of the tensor veli palatini muscle. In 11 of 13 cases, both the site of minimum cross-sectional area and the site of minimum circumference of the ET lumen were located in the cartilaginous portion of the ET, near the anterior margin of the junctional portion. In the 2 remaining cases, the site of minimum circumference was located in the junctional portion of the ET, whereas the site with the narrowest cross-sectional area stayed in the cartilaginous portion. The site of minimum circumference shifted significantly in the direction of the tympanic orifice of the ET, relative to the site of minimum cross-sectional area (p < .01). The average distance between these sites was 2.01 ± 1.75 mm. There was no significant difference between children (n = 6) and adults (n = 7). The so-called isthmus portion of the ET, located between the cartilaginous and bony portions, has been considered traditionally as the narrowest site through the entire ET. However, our results suggest that the narrowest portion of the ET lumen is located in the cartilaginous portion in both closed and open states.