Eustachian Tube

EUSTACHIAN TUBE/AUDITORY TUBE/PHARYNGOTYMPANIC TUBE

• 36mm long in adults(Range 32-38 mm)
  
• Runs downwards, forwards and medially from tympanic end
  
• Two parts – Postero lateral bony part (12mm) and Antero medial fibro cartilaginous part (24mm)

Auditory tube is formed by Elastic Cartilage.

• Two parts meet at the isthmus – narrowest part of ET
  
• Tympanic end (bony) – anterior wall of middle ear.
  
• Pharyngeal end – lateral wall of nasopharynx, it raises an elevation called torus tubarius 1 cm behind the posterior end of inferior turbinate.

Eustachian Tube develops from the first and second pharyngeal arch.

3 muscles –

• tensor veli palatini(dilator tubae) opens tubal lumen
  
• levator veli palatini
  
• salpingopharyngeus

Ostmann’s pad of fat- helps the tube closed at pharyngeal end

Lined by pseudo stratified ciliated columnar, cilia beat in the direction of nasopharynx.

Normally Eustachian tube (ET) is closed and opens intermittently during yawning, swallowing and sneezing through  contraction of Tensor vili palatini and Levator veli palatini muscle.

NERVE SUPPLY OF EUSTACHIAN TUBE

• Tympanic branch of 9th cranial nerve supplies sensory as well as secretomotor fibres
• Tensor veli palatine- mandibular branch of 5th nerve
• Levator veli palatine and salpingopharyngeus – pharyngeal plexus

BLOOD SUPPLY OF EUSTACHIAN TUBE

•  Ascending pharyngeal artery
•  Middle meningeal artery
• Artery of pterygoid canal

INFANT AND ADULT EUSTACHIAN TUBE DIFFERENCES

• Size of infant’s Eustachian Tube is 13-18mm at birth as compared to 36 mm in Adults.
• At birth,the angulation of tube is 10 degree with horizontal which becomes adult angulation of 45 degree with horizontal at 7 years of age.
• In infant’s ET,no anulation is present at Isthmus as compared to angulation present at Isthmus in Adults.
• In Infant’s ET,Bony part slightly longer than 1/3rd of the total length
• In infant’s ET,Tubal Cartilage is Flaccid due to which reflux of nasopharyngeal secretions may occur as compared to Adult’s ET in the Tubal Cartilage is comparitively rigid.
• In Infant,Ostmann pad of fat is comparitively less in volume as compared to the adults.
• Elastin content is higher in adult’s ET.

FUNCTIONS OF EUSTACHIAN TUBE

•  Ventilation & regulation of middle ear pressure
•  Protection against nasopharyngeal sound pressure and reflux of nasopharyngeal secretions
•  Clearance of middle ear secretions 

TESTS FOR EUSTACHIAN TUBE PATENCY

• Valsalva test
• Methylene blue test 
• Sonotubometry
• Politzer test
• Toynbee test 
• Frenzel maneuver
• Catheterization
• Inflation – Deflation test

LYMHATIC DRAINAGE OF EUSTACHIAN TUBE

• Retropharyngeal Lymph Nodes-Upper Jugular Chain

CLINICAL SIGNIFICANCE OF EUSTACHIAN TUBE

• Cholesteatoma invading Eustachian tube is an indication for Radical Mastoidectomy.
• Patency of Eustachian Tube is closed  and communication of middle ear with ET is obliterated during Radical Mastoidectomy.
• Sphenopetrosal synchondrosis is cartilagenous union b/w lateral half margin of great wing of sphenoid & petrous bone. On the under surface of sphenopetrosal synchondrosis, is a furrow, the sulcus of auditory tube for lodgement of cartilagenous part of auditory tube.
• Otoscopic findings of Eustachian tube dysfunction are Malleus is easily visible,Lusterless tympanic membrane,No movement of the tympanic membrane on siegel’s method,distorted light image on the anterior quadrant of tympanic membrane.
• Common cause of eustachian tube diseases is Adenoids.
• Throat infection causes Ear infection through Eustachian Tube.
• Eustachian tube gets blocked if pressure difference is more than 90 mm.
• Structures seen on posterior Rhinoscopy are Both choanae ,Posterior end of nasal septum ,Opening of Eustachian Tube,Posterior end of superior/tube  middle and inferior turbinates,Fossa of Rosenmuller,Torus Tubarius, Adenoids ,Roof and posterior wall and nasopharynx.