Characteristics of the Eustachian tube in children

1. Anatomy

The Eustachian tube is arched, the entire tube is about 35 to 39 mm long, and consists of two parts: the cartilaginous part and the bony part. Its outer 1/3 is bony, the internal carotid artery is located inside, and the tympanic opening is located in the upper part of the anterior wall of the tympanic cavity; the inner 2/3 is cartilaginous, and the pharyngeal opening at the medial end is located on the side wall of the nasopharynx, specifically at the posterior and inferior part of the posterior end of the inferior turbinate. The bony part is the shorter outer part of the tube, and its tympanic end opens into the anterior wall of the tympanic cavity; the cartilaginous part passes through the pharyngeal opening of the Eustachian tube and opens into the lateral wall of the nasopharynx. The cartilaginous part is usually closed and only opens when swallowing or yawning to balance the air pressure in the middle ear and outer ear, which is conducive to the normal vibration of the eardrum. Because the Eustachian tube is connected to the nasopharynx, pharyngeal infection can easily invade the tympanic cavity along the Eustachian tube and cause otitis media.

The Eustachian tube extends inward, forward, and downward from the tympanic opening to the pharyngeal opening, tilted at an angle of approximately 40 degrees to the horizontal plane. The tympanic opening is 2 to 2.5 cm higher than the pharyngeal opening and is funnel-shaped. It is the widest part of the bone inner diameter, about 4.5 mm, and becomes narrower as it goes inward. It is narrowest at the junction of the bone and cartilage, with an inner diameter of only 1 to 2 mm. From here, the canal gradually widens towards the pharyngeal opening, reaching its widest point at the pharyngeal opening, with upper and lower diameters reaching up to 9 mm.

The Eustachian tube is located in a hidden location and is not easy to teach when studying anatomy. In the outpatient clinic, the pharyngeal opening of the Eustachian tube can only be seen through a nasopharyngeal endoscope. It is even more difficult to see the tympanic cavity opening clearly. Only when the tympanic membrane is lifted up to explore the tympanic cavity can its trumpet-shaped opening be seen. The tubular part of the Eustachian tube is more of a potential muscular tube, and its true appearance can only be revealed when a considerable portion of the skull anatomical specimen is removed.

The Eustachian tube mucosa is connected to the tympanic cavity mucosa of the nasopharynx and is composed of pseudostratified ciliated columnar epithelial cells with a considerable number of secretory cells. The fluid secreted by these cells maintains the appropriate tension in the Eustachian tube, so that it is neither completely open nor able to open occasionally at appropriate opportunities, such as opening the mouth, swallowing, yawning or chewing, thereby regulating the pressure inside the tympanic cavity and maintaining the balance of pressure inside and outside the tympanic cavity.

The Eustachian tube is the only channel for ventilation and drainage of the middle ear. Its main function is to guide nasopharyngeal gas into the tympanic cavity to maintain pressure balance on both sides of the tympanic membrane, thereby ensuring normal vibration of the tympanic membrane. If the Eustachian tube is blocked or the nasopharyngeal opening is closed due to inflammation, the pressure in the tympanic cavity will decrease and the external pressure will increase relatively, causing the tympanic membrane to collapse and affect hearing. At this time, Eustachian tube catheter inflation is advisable.