Eustachian Tube and Its Disorders PDF

Chapter 9 Eustachian Tube and Its Disorders ANATOMY LINING OF THE EUSTACHIAN TUBE Histologically, the mucosa shows pseudostratified cilia...

Chapter 9 Eustachian Tube and Its Disorders ANATOMY LINING OF THE EUSTACHIAN TUBE Histologically, the mucosa shows pseudostratified ciliated Eustachian tube, also called auditory or pharyngotympanic columnar epithelium interspersed with mucous secreting tube, connects nasopharynx with the tympanic cavity. In goblet cells. Submucosa, particularly in the cartilaginous an adult, it is about 36 mm long and runs downwards, part of the tube, is rich in seromucinous glands. The cilia forwards and medially from its tympanic end, forming beat in the direction of nasopharynx and thus help to an angle of 45° with the horizontal. It is divided into drain secretions and fluid from the middle ear into the two parts: bony, which is posterolateral, forms one-third nasopharynx. (12 mm) of the total length and fibrocartilaginous, which is anteromedial, forms two-thirds (24 mm). The two parts meet at isthmus which is the narrowest part of the NERVE SUPPLY tube (Figure 9.1). The fibrocartilaginous part of the tube Tympanic branch of cranial nerve (CN) IX supplies sen- is made of a single piece of cartilage folded upon itself sory as well as parasympathetic secretomotor fibres to the in such a way that it forms the whole of medial lamina, tubal mucosa. Tensor veli palatini muscle is supplied by roof and a part of the lateral lamina; the rest of its lateral mandibular branch of trigeminal (V3) nerve. Levator veli lamina is made of fibrous membrane. palatini and salpingopharyngeus muscles receive motor The tympanic end of the tube is bony, measures nerve supply through pharyngeal plexus (cranial part of 5 × 2 mm and is situated in the anterior wall of middle CN XI through vagus). ear, a little above the level of floor. The pharyngeal end of the tube is slit-like, vertically. The cartilage at this end raises an elevation called torus tubarius, which is situated DIFFERENCES BETWEEN THE INFANT AND in the lateral wall of the nasopharynx, 1–1.25 cm behind ADULT EUSTACHIAN TUBE the posterior end of inferior turbinate. The eustachian tube of infants is wider, shorter and more horizontal; thus infections from the nasopharynx can easily reach the middle ear. Even the milk may regurgitate STRUCTURE into the middle ear if the infants are not fed in head-up position (see Table 9.1). MUSCLES RELATED TO EUSTACHIAN TUBE (FIGURE 9.2) Three muscles are related to the tube: tensor veli palatini, FUNCTIONS levator veli palatini and salpingopharyngeus. The medial Physiologically, eustachian tube performs three main fibres of the tensor veli palatini are attached to the lateral functions: lamina of the tube and when they contract help to open the tubal lumen. These fibres have also been called dilator 1. Ventilation and thus regulation of middle ear pressure. tubae muscle. The exact role of the levator veli palatini 2. Protection against (i) nasopharyngeal sound pressure and the salpingopharyngeus muscles to open the tube is and (ii) reflux of nasopharyngeal secretions. uncertain. It is believed that the levator veli palatini mus- 3. Clearance of middle ear secretions. cle, which runs inferior and parallel to the cartilaginous part of the tube forms a bulk under the medial lamina 1. VENTILATION AND REGULATION OF MIDDLE EAR and during contraction pushes it upward and medially PRESSURE. For normal hearing, it is essential that pres- thus assisting in opening the tube. sure on two sides of the tympanic membrane should be The elastin hinge. The cartilage, at the junction of me- equal. Negative or positive pressure in the middle ear af- dial, and lateral lamina at the roof, is rich in elastin fibres fects hearing. Thus, eustachian tube should open peri- which form a hinge. By its recoil it helps to keep the odically to equilibrate the air pressure in the middle ear tube closed when no longer acted upon by dilator tubae with the ambient pressure. Normally, the eustachian tube muscle. remains closed and opens intermittently during swallow- Ostmann’s pad of fat. It is a mass of fatty tissues relat- ing, yawning and sneezing. Posture also affects the func- ed laterally to the membranous part of the cartilaginous tion; tubal opening is less efficient in recumbent position tube. It also helps to keep the tube closed and thus pro- and during sleep due to venous engorgement. Tubal func- tect it from the reflux of nasopharyngeal secretions. tion is also poor in infants and young children and thus 61 mebooksfree.com 62 SECTION I — Diseases of Ear responsible for more ear problems in that age group. It normal hearing. Normally, the eustachian tube remains usually normalizes by the age of 7–10 years. closed and protects the middle ear against these sounds. A normal eustachian tube also protects the middle ear 2. PROTECTIVE FUNCTIONS. Abnormally, high sound from reflux of nasopharyngeal secretions into the middle pressures from the nasopharynx can be transmitted to ear. This reflux occurs more readily if the tube is wide in the middle ear if the tube is open thus interfering with diameter (patulous tube), short in length (as in babies) or the tympanic membrane is perforated (cause for persis- tence of middle ear infections in cases of tympanic mem- brane perforations). High pressures in the nasopharynx can also force na- sopharyngeal secretions into the middle ear, e.g. forceful nose blowing, closed-nose swallowing as in the presence of adenoids or bilateral nasal obstruction. 3. CLEARANCE OF MIDDLE EAR SECRETIONS. Mucous membrane of the eustachian tube and anterior part of the middle ear is lined by ciliated columnar cells. The cilia beat in the direction of nasopharynx. This helps to clear the secretions and debris in the middle ear to- wards the nasopharynx. The clearance function is fur- ther augmented by active opening and closing of the tube. EUSTACHIAN TUBE FUNCTION TESTS 1. VALSALVA TEST. The principle of this test, as also of Figure 9.1. Horizontal section through the eustachian tube showing politzerization, is to build positive pressure in the naso- bony and cartilaginous parts, isthmus, tympanic and pharyngeal ends. pharynx so that air enters the eustachian tube. To do this Figure 9.2. Vertical section through eustachian tube. Note: Cartilage of the tube forms medial wall, roof and part of lateral wall. Elastin is situated in the roof at the junction of medial and lateral laminae and helps the medial laminae to regain its original position of closure. (A) Eustachian tube is closed in resting position. (B) Tube is open when tensor veli palatini (dilator tubae) muscle contracts. TABLE 9.1 DIFFERENCES BETWEEN INFANT AND ADULT EUSTACHIAN TUBE Infant Adult Length 13–18 mm at birth (about half as long as in adult) 36 mm (31–38 mm) Direction More horizontal. At birth, it forms an angle of 10° Forms an angle of 45° with the horizontal with the horizontal. At age 7 and later it is 45° Angulation at isthmus No angulation Angulation present Bony versus cartilaginous part Bony part is slightly longer than one-third of the Bony part one-third; cartilaginous part two-thirds total length of the tube and is relatively wider Tubal cartilage Flaccid. Retrograde reflux of nasopharyngeal Comparatively rigid. Remains closed and protects secretions can occur the middle ear from the reflux Density of elastin at the hinge Less dense; tube does not efficiently close by recoil Density of elastin more and helps to keep the tube closed by recoil of cartilage Ostmann’s pad of fat Less in volume Large and helps to keep the tube closed mebooksfree.com  Chapter 9 — Eustachian Tube and Its Disorders 63 test, patient pinches his nose between the thumb and in- (b) Bleeding from the nose. dex finger, takes a deep breath, closes his mouth and tries (c) Transmission of nasal and nasopharyngeal infection to blow air into the ears. If air enters the middle ear, the into the middle ear causing otitis media. tympanic membrane will move outwards, which can be (d) Rupture of atrophic area of tympanic membrane if verified by otoscope or the microscope. In the presence too much pressure is used. of a tympanic membrane perforation, a hissing sound is produced or if discharge is also present in the middle 4. TOYNBEE’S TEST. While the above three tests use a ear, cracking sound will be heard. Failure of this test does positive pressure, Toynbee’s manoeuvre causes negative not prove blockage of the tube because only about 65% pressure. It is a more physiological test. It is performed of persons can successfully perform this test. This test by asking the patient to swallow while nose has been should be avoided (i) in the presence of atrophic scar of pinched. This draws air from the middle ear into the na- tympanic membrane which can rupture and (ii) in the sopharynx and causes inward movement of tympanic presence of infection of nose and nasopharynx where in- membrane, which is verified by the examiner otoscopi- fected secretions are likely to be pushed into the middle cally or with a microscope. ear causing otitis media. 5. TYMPANOMETRY (ALSO CALLED INFLATION–DEFLATION 2. POLITZER TEST. This test is done in children who are TEST). In this test, positive and negative pressures are cre- unable to perform Valsalva test. In this test, olive-shaped ated in the external ear canal and the patient swallows re- tip of the Politzer’s bag is introduced into the patient’s peatedly. The ability of the tube to equilibrate positive and nostril on the side of which the tubal function is desired negative pressures to the ambient pressure indicates nor- to be tested. Other nostril is closed, and the bag com- mal tubal function. The test can be done both in patients pressed while at the same time the patient swallows (he with perforated or intact tympanic membranes (see p. 26). can be given sips of water) or says “ik, ik, ik.” By means of an auscultation tube, connecting the patient’s ear under 6. RADIOLOGICAL TEST. A radio-opaque dye, e.g. hy- test to that of the examiner, a hissing sound is heard if paque or lipoidal instilled into the middle ear through a tube is patent. Compressed air can also be used instead pre-existing perforation and X-rays taken should deline- of Politzer’s bag. The test is also used therapeutically to ate the tube and any obstruction. The time taken by the ventilate the middle ear. dye to reach the nasopharynx also indicates its clearance function. This test is no longer popular now. 3. CATHETERIZATION. In this test, nose is first anaesthe- tized by topical spray of lignocaine and then a eustachian 7. SACCHARINE OR METHYLENE BLUE TEST. Saccharine tube catheter, the tip of which is bent, is passed along the solution is placed into the middle ear through a pre-ex- floor of nose till it reaches the nasopharynx. Here it is ro- isting perforation. The time taken by it to reach the phar- tated 90° medially and gradually pulled back till it engag- ynx and impart a sweet taste is also a measure of clearance es on the posterior border of nasal septum (Figure 9.3A). function. It is then rotated 180° laterally so that the tip lies against Similarly, methylene blue dye can be instilled into the the tubal opening (Figure 9.3B). A Politzer’s bag is now middle ear and the time taken by it to stain the pharyn- connected to the catheter and air insufflated. Entry of air geal secretions can be noted. into the middle ear is verified by an auscultation tube. Indirect evidence of drainage/clearance function is es- The procedure of catheterization should be gentle as it is tablished when ear drops instilled into the ear with tym- known to cause complications such as: panic membrane perforation cause bad taste in throat. (a) Injury to eustachian tube opening which causes scar- 8. SONOTUBOMETRY. A tone is presented to the nose and ring later. its recording taken from the external canal. The tone is Figure 9.3. Catheterization of eustachian tube (see text). mebooksfree.com 64 SECTION I — Diseases of Ear heard louder when the tube is patent (compare patulous eu- TABLE 9.3 CAUSES OF EUSTACHIAN TUBE stachian tube). It also tells the duration for which the tube OBSTRUCTION remains open. It is a noninvasive technique and provides information on active tubal opening. Accessory sounds Upper respiratory infection (viral or bacterial) Allergy produced in the nasopharynx, during swallowing, may in- Sinusitis terfere with the test results. The test is under development. Nasal polyps Deviated nasal septum Hypertrophic adenoids DISORDERS OF EUSTACHIAN TUBE Nasopharyngeal tumour/mass Cleft palate Submucous cleft palate 1. TUBAL BLOCKAGE. Normally, eustachian tube is Down syndrome closed. It opens intermittently during swallowing, yawn- Functional ing and sneezing through the active contraction of tensor veli palatini muscle. Air, composed of oxygen, carbon di- oxide, nitrogen and water vapour, normally fills the mid- retracted tympanic membrane, congestion along the dle ear and mastoid. When tube is blocked, first oxygen is handle of malleus and the pars tensa, transudate behind absorbed, but later other gases, CO2 and nitrogen also dif- the tympanic membrane, imparting it an amber colour fuse out into the blood. This results in negative pressure and sometimes a fluid level with conductive hearing loss. in the middle ear and retraction of tympanic membrane. In severe cases, as in barotrauma, tympanic membrane If negative pressure is still further increased, it causes is markedly retracted with haemorrhages in subepithelial “locking” of the tube with collection of transudate and layer, haemotympanum or sometimes a perforation. later exudate and even haemorrhage. Effects of acute and long-term tubal blockage are shown in Table 9.2. 2. ADENOIDS AND EUSTACHIAN TUBE FUNCTION. Ad- Eustachian tube obstruction can be mechanical, func- enoids cause tubal dysfunction by: tional or both. Mechanical obstruction can result from (i) intrinsic causes such as inflammation or allergy or (ii) (a) Mechanical obstruction of the tubal opening. extrinsic causes such as tumour in the nasopharynx or (b) Acting as reservoir for pathogenic organisms. adenoids. Functional obstruction is caused by collapse of (c) In cases of allergy, mast cells of the adenoid tissue re- the tube due to increased cartilage compliance, which re- lease inflammatory mediators which cause tubal block- sists opening of the tube or failure of active tubal-opening age. mechanism due to poor function of tensor veli palatini. Thus, adenoids can cause otitis media with effusion The common clinical conditions which can cause tubal or recurrent acute otitis media. Adenoidectomy can help obstruction are listed in Table 9.3. both these conditions. Symptoms of tubal occlusion include otalgia, which may be mild to severe, hearing loss, popping sensation, 3. CLEFT PALATE AND TUBAL FUNCTION. Tubal function tinnitus and disturbances of equilibrium or even vertigo. is disturbed in cleft palate patients due to: Signs of tubal occlusion will vary and depend upon the acuteness of the condition and severity. They include (a) Abnormalities of torus tubarius, which shows high elastin density making tube difficult to open. (b) Tensor veli palatini muscle does not insert into the TABLE 9.2 EFFECTS OF ACUTE AND PROLONGED torus tubarius in 40% cases of cleft palate and where TUBAL BLOCKAGE it does insert, its function is poor. Acute Otitis media with effusion is common in these pa- Acute tubal blockage tients. Even after repair of the cleft palate deformity, ↓ many of them require insertion of grommets to ventilate Absorption of ME gases the middle ear. ↓ Negative pressure in ME 4. DOWN SYNDROME AND TUBAL FUNCTION. Function of ↓ Retraction of TM eustachian tube is defective possibly due to poor tone of ↓ tensor veli palatini muscle and abnormal shape of naso- Transudate in ME/haemorrhage (acute OME) pharynx. Children with this syndrome are prone to fre- Prolonged quent otitis media or otitis media with effusion. Prolonged tubal blockage/dysfunction ↓ 5. BAROTRAUMA. See p. 71. OME (thin watery or mucoid discharge) ↓ Atelectatic ear/perforation ↓ RETRACTION POCKETS AND EUSTACHIAN Retraction pocket/cholesteatoma TUBE ↓ Erosion of incudostapedial joint In ventilation of the middle ear cleft, air passes from eus- tachian tube to mesotympanum, from there to attic, adi- ME, middle ear; TM, tympanic membrane; OME, otitis media with effusion. tus, antrum and mastoid air cell system. Mesotympanum mebooksfree.com  Chapter 9 — Eustachian Tube and Its Disorders 65 communicates with the attic via anterior and posterior administration of potassium iodide is helpful but some isthmi, situated in membranous diaphragm between the long-standing cases may require cauterization of the mesotympanum and the attic. Anterior isthmus is situ- tubes or insertion of a grommet. ated between tendon of tensor tympani and the stapes. Posterior isthmus is situated between tendon of stapedius muscle and pyramid, and the short process of incus. In EXAMINATION OF EUSTACHIAN TUBE some cases, middle ear can also communicate directly Pharyngeal end of the eustachian tube can be examined with the mastoid air cells through the retrofacial cells. by posterior rhinoscopy, rigid nasal endoscope or flexible Any obstruction in the pathways of ventilation can nasopharyngoscope. The extrinsic causes which obstruct cause retraction pockets or atelectasis of tympanic mem- this end can be excluded (Figure 9.4). brane, e.g. Tympanic end of the tube can be examined by micro- 1. Obstruction of eustachian tube → Total atelectasis of scope or endoscope, if there is a pre-existing perforation. tympanic membrane. Eustachian tube endoscopy or middle ear endoscopy can 2. Obstruction in middle ear → Retraction pocket in poste- be done with very fine flexible endoscopes. Simple exami- rior part of middle ear while anterior part is ventilated. nation of tympanic membrane with otoscope or micro- 3. Obstruction of isthmi → Attic retraction pocket. scope may reveal retraction pockets or fluid in the middle 4. Obstruction at aditus → Cholesterol granuloma and ear. Similarly, movements of tympanic membrane with collection of mucoid discharge in mastoid air cells, respiration point to patulous eustachian tube. while middle ear and attic appear normal. Further assessment of function of the tube can be made by Valsalva, politzerization, Toynbee and other tests al- Depending on the location of pathologic process, oth- ready described. er changes such as thin atrophic tympanic membrane, Aetiologic causes of eustachian tube dysfunction can be partial or total (due to absorption of middle fibrous layer), assessed by thorough nasal examination including endos- cholesteatoma, ossicular necrosis and tympanosclerotic copy, tests of allergy, CT scan of temporal bones and of changes may also be found. paranasal sinuses. MRI may be required to exclude multi- Principles of management of retraction pockets and ple sclerosis in patulous eustachian tube. atelectasis of middle ear would entail correction/repair of the irreversible pathologic processes and establishment of the ventilation. PATULOUS EUSTACHIAN TUBE In this condition, the eustachian tube is abnormally pat- ent. Most of the time it is idiopathic but rapid weight loss, pregnancy especially third trimester, or multiple sclerosis can also cause it. Patient’s chief complaints are hearing his own voice (autophony), even his own breath sounds, which is very disturbing. Due to abnormal potency, pressure changes in the nasopharynx are easily transmitted to the middle ear so much so that the movements of tympanic can be seen with inspiration and expiration; these movements are further exaggerated if patient breathes after closing Figure 9.4. Endoscopic view of nasopharynx showing torus tubarius the opposite nostril. in the right lateral wall of nasopharynx. Note also the fossa of Rosen- Acute condition of patulous tube is self-limiting and müller which lies behind it. Fossa of Rosenmüller is the commonest site does not require treatment. In others, weight gain, oral for the origin of carcinoma nasopharynx. mebooksfree.com