Auditory tube/ Pharyngotympanic tube/ Eustachian tube

 Auditory tube is also known as the pharyngotympanic tube or the eustachian tube.

The auditory tube is a trumpet-shaped channel
which connects the middle ear cavity with the nasopharynx. 

It is about 4 cm long, and
is directed downwards, forwards and medially. It forms an angle of 45 degrees with the sagittal plane and 30 degrees with the horizontal plane.
The tube is divided into bony and cartilaginous parts 

The bony part forms the posterior and lateral one- third of the tube.
It is 12 mm long, and
lies in the petrous temporal bone near the tympanic plate. 

Its lateral end is wide and opens on the anterior wall of the middle ear cavity.
The medial end is narrow (isthmus) and is jagged
for attachment of the cartilaginous part. 

The lumen of the tube is oblong being widest from side to side. 

Relations 

Superior : Canal for the tensor tympani
Medial: Carotid canal.
Lateral: Chorda tympani nerve, spine of sphenoid, auriculotemporal nerve and the temporomandibular joint. 

CARTILAGINOUS PART 

The cartilaginous part forms the anterior and medial two-thirds of the tube.
It is 25 mm long, and
lies in the sulcus tubae, a groove between the greater wing of the sphenoid and the apex of the petrous temporal. 

It is made up of a triangular plate of cartilage which is curled to form the superior and medial walls of the tube.
The lateral wall and floor are completed by a fibrous membrane. 

The apex of the plate is attached to the medial end of the bony part.
The base is free and forms the tubal elevation in the nasopharynx 

Relations 

Anterolaterally: Tensor veli palatini, mandibular nerve and its branches, otic ganglion, chorda tympani, middle meningeal artery and medial pterygoid plate. 

Posteromedially: Petrous temporal and levator veli palatini.
The levator veli palatini is attached to its inferior surface, and the salpingopharyngeus to lower part near the pharyngeal opening. 

Vascular Supply 

The arterial supply of the tube is derived from the ascending pharyngeal and middle meningeal arteries and the artery of the pterygoid canal.
The veins drain into the pharyngeal and pterygoid plexuses of veins.
Lymphatics pass to the retropharyngeal nodes. 

Nerve Supply 

1. At the ostium, by the pharyngeal branch of the pterygopalatine ganglion suspended by the maxillary nerve.
2. Cartilaginous part, by the nervus spinosus branch of mandibular nerve.
3. Bony part, by the tympanic plexus formed by glossopharyngeal nerve. 

Function 

The tube provides a communication of the middle ear cavity with the exterior, thus ensuring equal air pressure on both sides of the tympanic membrane. 

The tube is usually closed.
It opens during swallowing, yawning and sneezing, by the actions of the tensor and levator veli palatini muscles. 

Clinical Anatomy 

Infections may pass from the throat to the middle ear through the auditory tube,
This is more common in children because the tube is shorter, wider and straighter in them Inflammation of the auditory tube (eustachian catarrh) is often secondary to an attack of common cold, or of sore throat.
This causes pain in the ear which is aggravated by swallowing, due to blockage of the tube.
Pain is relieved by instillation of decongestant drops in the nose, which helps to open the ostium. 

The ostium is commonly blocked in children by enlargement of the tubal tonsil. 

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Auditory Tube/Pharyngotympanic Tube/Eustachian Tube | Parts | Relations | Functions |