Corpus: Auditory tube

The auditory tube, measuring approximately 30 to 35 mm in length, connects the tympanic cavity of the middle ear to the nasopharynx. It extends from the mesotympanum diagonally forwards and downwards to the nasopharynx, and is lined with ciliated respiratory epithelium.

The auditory tube comprises two sections:

• Bony part: Constituting the proximal one-third adjacent to the tympanic cavity, referred to as pars ossea.
• Cartilaginous part: Making up the distal two-thirds towards the nasopharynx, known as pars cartilaginea.

The transition between these parts is marked by a physiological narrowing called the isthmus tubae auditivae.

The auditory tube opens into the nasopharynx at the pharyngeal tubal ostium (ostium pharyngeum tubae auditivae) and into the tympanic cavity at the tympanic tubal ostium (ostium tympanicum tubae auditivae). Near the nasopharyngeal opening, two mucosal protrusions are evident:

• The tubal protuberance, positioned above the tubal ostium
• The levator cushion, located below the tubal ostium

The auditory tube is innervated by the tympanic nerve.

The auditory tube originates from the proximal segment of the tubotympanic recess, which is an outgrowth of the first pharyngeal pouch.

The tube is lined with ciliated epithelium; the pars ossea contains a monolayer, while the pars cartilaginea features a multilayered lining. The cartilaginous section includes elastic cartilage, referred to as tubal cartilage.

The auditory tube plays a crucial role in equalizing pressure between the middle ear and nasopharynx, essential for maintaining hearing capability under varying air pressure. It also facilitates drainage from the middle ear. Blockages can lead to tympanic effusion.

Physiologically, the auditory tube remains closed to protect against nasopharyngeal infections. It opens during activities such as swallowing, yawning, or speaking certain sounds. The tube's passive closure involves the peritubular vascular plexus and Ostmann's fat body, while the tubal cartilage aids in mechanical closure, functioning like a spring. This cartilage is hook-shaped and comprises:

• Lateral lamina of cartilage of auditory tube (thin end)
• Medial lamina of cartilage of auditory tube (thick end)

The tube's opening mechanism is controlled by three muscles:

• Tensor veli palatini muscle: Attaches to the thin end of the closure cartilage, counteracting the cartilage's tension.
• Levator veli palatini muscle: Attaches beneath the tubal cartilage, elevating it.
• Salpingopharyngeus muscle: Connects to the thick medial tubal cartilage, regulating the upward movement of the levator veli palatini muscle and extending into the pharyngeal sidewall.

Clinically, the auditory tube's functionality is assessed using a tube function test. Chronic blockage can lead to tubal catarrh, whereas a failure to close, known as tuba aperta, is characterized by autophony.