Anatomy of external ear, embryology and clinical significance

anatomy of external ear

1. External Ear Dr.Suman Chaulagain ENT Resident HAMS Hospital Embryology Anomalies Structure Blood supply Nerve supply Lymphatic drainage Clinical and surgical importance

2. Contents Embryology Anomalies Structure Blood supply Nerve supply Lymphatic drainage Clinical and surgical importance

3. Pharyngeal apparatus Composed of Pharyngeal(Brachial) C lefts, A rches, P ouches. Pharyngeal C lefts- derived from E ctoderm. Also called pharyngeal grooves. P haryngeal A rches—derived from M esoderm (muscles, arteries) and neural crest (bones, cartilage). Pharyngeal P ouches—derived from E ndoderm.

4. At 5 weeks of gestation, 5 paired structures(1,2,3,4,6 pharyngeal arch) are visible Externally. External Ear: 1 st & 2 nd pharyngeal arch.

5. The embryologic source and the time of development of external and middle ears are independent of the inner ear development. Therefore malformed and non-functional inner ear can have normal external and middle ears and vice versa.

6. Embryology Development of external ear At 6 weeks of embryonic life, S ix Tubercles(hillock of his) appears around first pharyngeal cleft . Tragus, helix & cymba concha develop from hillocks arising from 1 st pharyngeal arch. Concha cavum , antihelix and antitragus arise from the hillocks of the second arch. Initially developing pinna is located in the neck. and, by the 20 th week of gestation, pinna attains adult shape.

7. External A uditory Canal Development EAC develops from deepening of the first pharyngeal cleft. The 1 st pharyngeal pouch deepens to contact the first cleft. As the embryonic connective tissue proliferates between the first pouch and the first cleft, the contact between the two developing structures is lost and the meatal plate develops. The meatal plate starts to canalize between 21 and 28 weeks , forming the inner two-third of the EAC. The innermost plate contribute to the outer layer of the tympanic membrane.

8. Developmental anomalies Preauricular sinus Preauricular appendages Microtia ( dimunitive ear)- isloated congenital abnormality. Associated with syndromes like: Fetal alcohol syndrome, Maternal Diabetic Mellitus, Thalidomide, Isotreninoin exposure. Anotia (Failure of development of hillock of his) Bat ear deformity(defective in development of 4 th tubercle) Cryptotia (hidden/pocket ear) Polyotia (mirror ear)- due to persistence of preauricular tissue. Stahl’s bar ( satrio’s ears) Congenital canal atresia Syndromes associated with microtia and external ear abnormalities

9. Pre auricular sinus/cyst: commonly seen between the tragus and crus of helix. Due to faulty fusion between first and the second arch tubercles. tragus Crus of helix

10. Anomalies of External Auditory Canal Atresia-due to failure of meatal plug to canalize. Changes in curvature of canal Stenosis

11. Tympanic Membrane Development Develops by apposition of tubotympanic recess of 1 st pharyngeal pouch and 1 st pharyngeal cleft. 1. Outer cuticular layer : derived from Ectodermal lining of first pharyngeal cleft. 2. Intermediate fibrous layer :derived from intervening Mesoderm between the 1 st pharyngeal cleft and 1 st pharyngeal pouch. 3. Inner endodermal layer : derived from Endodermal lining of 1 st pharyngeal pouch.

12. Anatomy of External Ear

13. Anatomy of External E ar Pinna -paired structure. Size: 60mm in length. Medial surface-convex Lateral surface-concave with folds & hollows. Focus and aid in the localization of sound. superior margin of the pinna lies in line with the eyebrow, and the lower limit of the lobule is in line with the base of the nasal septal columella . Cartilagenous framework and non cartilagenous part(lobule) Skin of lateral and medial surface of the pinna possesses hair and both sebaceous and sudoriferous glands. Consists of extrinsic( auricularis anterior,posterior,superior ) and intrinsic muscles. 2 ligaments-anterior and posterior.

14. External features of auricle

15. Blood supply Arterial supply- E xternal Carotid A rtery Anterior auricular branches of superficial temporal artery. Posterior auricular artery. Superior auricular artery. Venous drainage -auricular veins correspond to the arteries of the auricle. - arteriovenous anastomoses are numerous in the skin of the auricle and are thought to be important in the regulation of core temperature.

16. Lymphatic drainage The posterior aspect of the pinna drains to nodes at the mastoid tip . The tragus and upper part of the pinna drain into preauricular nodes . The remaning part of the pinna drains to upper deep cervical lymph nodes.

17. Clinical Importance Incisura terminalis - devoid of cartilage, incision for procedures in ear to avoid postoperative perichondritis . Lateral surface -skin firmly adherent to perichondrium; so more prone for frost bite . Medial surface - more subcutaneous tissue, skin loosely adherent to underlying cartilage, so cyst like sebaceous cyst are common.

18. Stripping the perichondrium from the cartilage can result into hematoma formation which can lead to cartilage necrosis with crumpled up ‘’Boxer’s ears.’’ Small pieces of skin from the lobule of the pinna are used for identifying l epra bacilli to confirm the diagnosis of leprosy.

19. External auditory canal Extends from concha cavum to the tympanic membrane .(Length=24mm) The lateral 1/3 rd of EAC – cartilaginous framework. Contains hair follicles & glandular structures.(Length= 8mm ) The middle 2/3 rd of EAC- B ony canal . It is tightly adherent layer of epidermis.(Length= 16mm )

20. ‘’S’’ shaped -its outer part is directed u pwards, b ackwards and m edially while its inner part is directed d ownwards, f orwards and m edially. Therefore, to see the tympanic membrane, the pinna has to be pulled u pwards, b ackwards and l aterally so as to bring the two parts in alignment. In the Neonates , t ympanic bone is not fully developed, and the tympanic membrane is more h orizontally placed so that the auricle must be gentle drawn d ownwards and b ackwards for the best view of the tympanic membrane.

21. Isthmus - narrowest part of canal lying medial to junction of bony & cartilaginous parts nearly 5mm lateral to tympanic membrane. The roof & posterior wall of EAC are shorter than floor & anterior wall ; thus tympanic membrane fits obliquely in deeper end of the canal. Anterior recess -anterior wall of EAC goes sharply forward to the tympanic membrane to form a blind pouch. Tympanic sulcus -medial end of the bony canal is marked by a groove, the tympanic sulcus, which is absent superiorly.

22. Clinical importance Anterior recess - common site for foreign body impaction lodgment. Furunculosis -outer cartilaginous canal. Wax-impaction ( deafness,irrigatioin,itching,otalgia etc.) Tympanomastoidectomy - incision at 6, 12 O’ clock then curvilinear incision to join both to raise a flap(anteriorly attached with pedicle) which acts as vascular supply for graft.

23. Clincal importance Skin lining tympanic membrane and bony canal has self cleansing property due to migration of keratin layer of epithelium form drum towards cartilaginous portion. Loss of this property- keratosis obturans Involvement of the ear in herpes zoster of the geniculate ganglion depends on the connectioin between the auricular branch of the vagus and the facial nerve within the petrous temporal bone.

24. Irritation of the auricular branch of vagus nerve in the external ear by ear wax or syringing may reflexly produce persistent cough, vomiting or even death due to sudden cardiac inhibition. On the other hand, mild stimulation of this nerve may reflexly produce increased appetite. Accumulation of wax in the external acoustic meatus is often a source of excessive itching, although fungal infection and foreign bodies should be excluded. Troublesome impaction of large foreign bodies like seed, grains, insects is common.

25. Blood supply Arterial supply- derived from branches of the External Carotid artery. The auricular branches of the superficial temporal artery supply the roof and anterior portion of the canal . The deep auricular branch of the first part of the maxillary artery supplies the anterior meatal wall skin and the epithelium of the outer surface of the tympanic membrane . The auricular branches of the posterior auricular artery pierce the cartilage of the auricle and supply the posterior portions of the canal. Venous drainage- the veins drain into the External J ugular V ein , the maxillary veins and the pterygoid plexus .

26. Nerve supply Anterior wall and roof : Auriculotemporal branch of mandibular nerve(V3) Posterior wall and floor : Auricular branch of vagus (CN X) Posterior wall of the auditory canal also receives sensory fibers of CN VII through auricular branch of vagus .

27. Lymphatic drainage of EAC Anterior wall - pre-auricular Lymphnode Posterior wall - post auricular Lymphnode Floor - R etroauricular Lymphnode

28. Tympanic membrane

29. Tympanic membrane

30. Tympanic membrane Thin semi-translucent membrane. Pearly white in color, oval in shape. Lies obliquely at an angle of 55 . Vertical Diameter- 10mm ; Horizontal Diameter- 9mm Inner surface is convex. Forms majority of lateral wall of middle ear cavity.  

31. Tympanic membrane Peripheral part is thicker and rounded(except in upper part)- annulus tympanicus Annulus is attached at its circumference to tympanic sulcus which ends in a notch know as ‘’NOTCH of RIVINUS’’ in upper part. Malleolar folds-anterior and posterior arising from notch of rivinus to lateral surface of malleus.

32. Tympanic membrane It has two parts: A)Pars tensa . Largest part below malleolar folds. Contains all 3 layers. Central part is tented inwards at the level of tip of malleus and is called UMBO. Anterioinferior part is the most illuminated part. B)Pars flaccida ( sharpnell’s membrane) T riangular area above malleolar folds T hin,devoid of fibrous tissue and annulus. It fits into notch of rinivus .

33. Tympanic membrane It has three layers 1.Outer cuticular /epithelial layer It is continuous with skin of EAC 2.Middle fibrous layer The lamina propria of the pars tensa has radial, circular , parabolic and transverse fibres . This arrangement is for tympanic membrane displacement during sound stimulation. In the pars flaccida , the lamina propria is less marked and the orientation of the collagen fibres seems random. 3.Inner mucosal layers It is continuous with middle ear mucosa.

34. Blood supply Arterial supply- Outer surface - manubrial artery, deep auricular branch of maxillary artery. Inner surface -anterior tympanic branch of maxillary artery. Inferior tympanic artery, branch of ascending pharyngeal artery.

35. Venous drainage Outer surface-external jugular vein Inner surface- transverse sinus and venous plexus around Eustachian tube

36. Nerve supply Lateral surface Anterior half- auriculotemporal nerve Posterior half- auricular branch of vagus Medial surface- Tympanic plexus(tympanic branch of CN IX( Jocobson’s nerve)

37. References Scott brown’s otorhinolaryngology, head & neck surgery Glasscock- Shambaugh surgery of the ear Gray’s anatomy Diseases of ENT & HNS – PL Dhingra , Shruti Dhingra

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