Changes of visualised Eustachian tube lengths by age and position: Radiologic study in sitting and supine positions using cone beam and conventional CT

Abstract

Objectives: Patulous eustachian tube (ET) has been characterised by the visualisation of full-length ET on computed tomography (CT) results. We wanted to investigate the changes of visualised ET lengths by age in supine and sitting positions. Design: Retrospective study. Setting: Tertiary care academic referral centre. Participants: One hundred subjects who underwent cone beam CT (CBCT) in a sitting position and conventional CT in a supine position for non-otitis-related or dental complaints. Main outcome measures: Visualised ET lengths from the nasopharyngeal orifice measured by different positions and ages. Results: Subjects did not show visualisation of full-length ET throughout the study. The visualised ET lengths (9.0 ± 2.5 mm) of the CBCT group were significantly larger than those (6.8 ± 2.3 mm) of the conventional CT group (P < 0.0001).Women showed longer visualised ET lengths than men in CBCT group (P < 0.001). The visualised ET lengths of the CBCT group were consistent or slightly increasing as a function of age (P = 0.06); however, the visualised ET lengths of the conventional CT group decreased as a function of age (P = 0.001). The slopes of regression lines of the two groups were significantly different. Conclusions: When in the supine position, the ET lengths gradually shortened as the subjects got older, most likely due to venous engorgement and the collapse of surrounding tissues; this finding thus suggests that CT in a supine position is an inappropriate method to diagnose patulous ET. The visualised ET lengths by CBCT in a sitting position were consistent throughout the different ages of the subjects and may be used as a diagnostic test for patulous ET.