Endoscopic assessment of eustachean tube function
Sunday, May 01 2011 @ 06:05 am IST
Contributed by: Admin
The eustachean tube connects the middle ear cavity with atmospheric air. It thus plays an important role in ventilating the middle
ear cavity, clearing the secretions from the middle ear cavity. It also plays a vital role in protecting the middle ear cavity from
the nasopharyneal secretions. Anatomically the proximal third of the eustachean tube is bony in nature and is lined by a thin
layer of respiratory epithelium. This portion of the tube is fixed in its dimensions and does not vary much.
The lateral 2/3 of this tube is cartilageanous. This portion of the eustachan tube is acted upon by
the peritubal muscles, hence its dimensions are variable.
How secretions are cleared from the middle ear cavity?
Secretions are cleared from the middle ear cavity by the following mechanisms:
By the mucociliary activity
Muscular pumping action that occurs due to tubal closing
The proximal bony portion of the eustachean tube is permanently open
The distal portion of the eustachean tube is closed at rest. It opens with active dilatation of the pharyngeal end of the
eustachean tube due to contraction of the peritubal muscles. This occurs primarily during swalling / yawning.
How is the middle ear protected from the secretions of nasopharynx?
The middle ear is protected from the reflux of secretions from the nasopharynx due to the normal closed position of the
pharyngeal end of the eustachean tube. The entrapped air in the middle ear cavity acts as a gas cushion preventing reflux.
Role of endoscopy in studying the function of eustachean tube:
Small diameter flexible endoscopes have been used to study the eustachean tube function. It should be remembered that the
narrowest portion of the eustachean tube is the isthumus area. The cross section of the isthumus is about 1 – 1.5 mm.
So 1 mm endoscopes are ideal tool for studying the function of ET.
Studies have shown that the act of swallowing produced transient opening of the eustachean tube. Repeated acts of
swallowing causes fatigue of peritubal muscles causing the eustachean tube to open only up to the level
of isthumus failing to open up the valve area. 1 mm flexible endoscopes can be passed through the pharyngeal end of eustachean tube to study its interiors.
These studies reveal the fundamental problems in eustachean tube dysfunctions.
These problems include:
Primay mucosal disease caused by infections, inflammation and allergy
Reflux from the nasopharynx
Anatomical obstruction due to congential abnormalities