Eustachian Tube (Anatomy, Physiology and Diagnostic Tests)

Anatomy 

Eustachian tube (ET) is also called auditory tube or pharyngo tympanic tube. This tube connects the lateral part of nasopharynx to the anterior wall of the tympanic cavity (middle ear).  ET is approximately 36mm in length. The lateral 1/3 of ET is bony. The medial 2/3 is cartilaginous. The narrowest part of ET is known as Isthmus. Isthmus is located on bony cartilaginous junction. The cartilaginous end of eustachian tube protrudes in nasopharynx called Torus Tubarius.  ET is an angle of 45 degrees to the horizontal plane. Incase of neonates, this ET is always horizontal and tube length is always half of it. It is almost 16-18mm. Since the ET is shorter and horizontal in children, so the children are more prone to middle ear infection.   ET has middle ear opening (5mmX2mm), has broader  opening in the pharynx (8mmX3mm). The narrowest part (junction of bone and cartlage)is approximately 3mm

This is a high-yield topic for ENT subject and it is highly important for NEET PG exam Preparation.

Ostmanns Pad of Fat

Keeps the eustachian tube in a closed position. The eustachian tube  is closed at rest and that is because of Ostmanns Pad of Fat. The median fibres of tensor veli palatini is the main opener or dilator of the eustachain tube. Also known as dilator tubee. When tensor vili palatini contract, pulls the cartilage of eustchian tube anteriorly, that leads to opening of the eustachian tube. Secondary function of the levator vili palatini is opening of the eustachian tube. 

Also read: Eustachian Tube (Anatomy, Physiology and Diagnostic Tests)

Tensor and Levator Vili Palatini

Eustachian tube opens in the lateral wall of the nasopharynx, just behind the nasal cavity. Levator pili palatini and tensor vili palatini attached to the anterior surface. Tensor vili palatini contracts and open the eustachian tube. Tensor vili palatini goes down , takes a turn in pterygoid hamulus and attached in the centre (soft palate). Patients of cleft palate has ET dysfunction that lead to middle ear disorders because in cleft palate the muscles wont able to meet in the centre.

Also read: Anatomy of Middle Ear - NEET PG ENT

Functions of Eustachian tube 

• It maintains middle ear air pressure equal to outside atmospheric pressure. Normally it is closed at rest. At yawning or swallowing, the soft palate moves, that leads to the contraction of tensor vilipalatini , which opens the eustachian tube, the air enters the middle ear and air pressure is restored.  The advantage of closing the eustachian tube at rest is that it prevents food  and infection going into the middle ear. 
• It drains middle ear secretions. The middle ear is lined by mucosa and its almost a closed cavity. It keeps on receiving air from the ET. Mucosa has a property that it absorbs oxygen from the surface, which means middle ear has more carbon dioxide and less oxygen as compare to atmospheric air. The advantage of low oxygen is that it prevents growing of aerobic bacteria in the middle ear. Therefore the middle ear is maintained as sterile environment. If there is tympanic membrane perforation or hole, the chance of infection and bacteria will increase. 

Euctashian Tube Function Test 

Passive test- Also known as non physiological test. 

1. Valsalva Maneuver- Ask the patient to close the nose and blow the cheeks. Positive pressure is generated in the naso pharynx. It forcefully opens the eustachian tube. The air will go in the middle ear and the tympanic membrane will bulge out. That shows that its anatomically normal. 
2. Politizer test- Done in children who are unable to perform valsalva test. It consist of bag. Insert the tip of the bag in the nose, close the nose and ask the child to keep the mouth close and press the bag. By pressing it will create pressure in the nose and euctashian tube, which opens the euctashian tube and tympanic membrane bulges out. 
3. Eustachian Tube Catheterization

This catheter has soft rounded ending with a bulge. On the other side the ring is present . The ring helps to identify the side of the turn.  Insert the ET cathether straight into the nasal cavity, pass it along into the nasopharynx and than rotate it medially and pull it back. The turn will engage behind the nasal septum. Rotate it by 180 degrees and enter into the eustachian tube. Attach the politizer bag and blow open the ET. 

Also read: Disorders of Nose and Paranasal Sinus - NEET PG ENT

Active Test - Also known as physiological test

1. Toynbee test-  The patient is asked to drink water against the closed nasal cavity. Swallowing generates the negative pressure against the closed nose.,which will lead to contraction of tensor vili palatini and that opens the eustachian tube.  The negative pressure of the nasopharynx and oropharynx will pull the air out of the middle ear, which causes retraction of the tympanic membrane. It’s a physiological test because the ET is being opened by the negative pressure. 
2. Tympanometry- also called inflation, deflation test. Insert probe in the ear. On the probe there is sound source, microphone (that receive how much sound is reflected back  after striking the tympanic membrane and pressure meter (in which  we can increase or decrease the pressure in the EAC). Ask the patient to do valsalva, the ET will open up, air will enter and tympanic membrane bulges out. Than ask the patient to do Toynbee test, patient swallows against the closed nose. It will generate the negative pressure and all the air will be sucked out and tympanic membrane will retract. The typanometry test can also be done even with a perforated membrane. 
3. Radiological Test- generally done in perforated tympanic membrane. Instill radio opaque dye in the middle ear, take an Xray, observe ET and check for obstruction.

In perforated tympanic membrane instead of dye can also instill saccharine . Saccharine has sweet taste, it will come in the throat. Can also use dye ( methylene blue) 

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Patulous Eustachian tube

When the eustachian tube is open at rest. The patulous eustachian tube will lead to autophony. The patient hear his only voice very loud. Patulous eustachian tube can happen incase of rapid weight loss or in pregnancy. Treatment- Scar the eustachian tube or inject fat in the eustachian tube.

 SONOTUBOMETRY

Sono means sound, tubometry is to check the eustachian tube function. This is the latest investigation. Sound is given in the nose, which reach in the middle ear and sound source can be picked up by a probe in the EAC. 

Chronic Eustachian Tube Disorders

The most disorders of the eustachian tube are because of the obstruction of the eustachian tube.  Obstruction can be due to mass, polyp, malignancy. In these condtions, treat the cause. However sometimes, because of the repeated infections, euctachian tube may undergo scarring, fibrosis. Because of that eustachian tube may undergo stenosis. In these chronic eustachian tube disoredrs, now a days eustachian tube balloon dialation is done. 

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