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40 The ear GRANT J.E.M. BATES

Surgical anatomy of the ear

The external ear consists of the pinna and the ear canal. The pinna is made of yelloelastic cartilage co!ered "y tightly adherent s#in. The external and middle ear de!elop

from the first to "ranchial arches. The external ear canal is $ cm in length% the outer

to&thirds is cartilage and the inner third is "ony. The s#in on the lateral surface of

the tympanic mem"rane and the inner to&thirds of the ear canal is highly specialised.

't does not simply shed li#e the s#in from the rest of the "ody. 't migrates outards

from the tympanic mem"rane and along the ear canal. As a result of this migration

most people(s ears are self&cleaning. )isorders of s#in migration can result in ear

disease *e.g. cholesteatoma+. The external canal is richly inner!ated and the s#in is

tightly "ound don to the perichondrium so that oedema in this region results in

se!ere pain.

The lymphatics of the external ear drain to the retro auricular% parotid% retropharyngealand deep upper cer!ical lymph nodes.

The middle ear contains the ossicles. ,aterally it is "ounded "y the tympanic

mem"rane% medially "y the cochlea% anteriorly "y the eustachian tu"e and posteriorly

it communicates ith the mastoid air cells *-ig. /.0+. Entined in this tiny space is

the facial ner!e hich pursues a tortuous course through the middle ear and exits the

s#ull "ase at the stylomastoid foramen. 1noledge of the anatomy of the middle ear

is important "ecause infection can spread through it to the cranial ca!ity hich lies

millimetres aay.

The tympanic mem"rane has three layers2 an inner mucosal layer% a dense fi"rous

middle layer and the outer stratified s3uamous epithelium *s#in+. The upper portion

that lies a"o!e the lateral process of the malleus is called the pars flaccida. The loerportion% ma#ing up the ma4ority of the drum% is called the pars tensa *-ig. /.5+.

The tympanic mem"rane and ossicles act as a transformer system con!erting

!i"rations in the air to !i"rations ithin the fluid&filled inner ear *perilymph+.The

e!olution of the middle ear is interesting. -ish do not ha!e one% hereas amphi"ians

*e.g. salamanders+ ha!e a single strut for an ossicle. At an air6ater interface there is

a $/ deci"els loss of sound energy. The mammalian middle ear o!ercomes !irtually

all of this potential loss of sound energy.

The inner ear comprises the cochlea and !esti"ular la"yrinth *saccule% utricle and

semicircular canals+. These structures are em"edded in dense "one called the otic

capsule. The cochlea is a minute spiral of to and three&3uarter turns. 7ithin this

spiral% perilymph and endolymph are partitioned "y the thinnest of mem"ranes

*Reissner(s mem"rane+. The endolymph has a high concentration of potassium similar

to intracellular fluid% and the perilymph has a high sodium concentration similar to

extracellular fluid. Maintenance of the ionic gradients is an acti!e process and is

essential for neuronal acti!ity.

There are approximately 08 /// hair cells in the human cochlea. They are arranged in

ros of inner and outer hair cells. The inner hair cells act as mechanicoelectric

transducers% con!erting the acoustic signal into an electric impulse. The outer hair

cells contain contractile proteins andha!e an efferent ner!e supply from the "rain.

They ser!e to tune the "asilar mem"rane on hich they are positioned.

Each inner hair cell responds to a particular fre3uency and hen stimulated itdepolarises and passes an impulse to the cochlea nuclei in the "rainstem.

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The !esti"ular la"yrinth consists of the semicircular canals% the utricle and saccule%

and their central connections. The three semicircular canals are arranged in the three

planes of space at right angles to each other. As in the auditory system% hair cells are

present. 'n the lateral canals the hair cells are em"edded in a gelatinous cupula% and

shearing forces% caused "y angular mo!ements of the head% produce hair cell

mo!ements and generate action potentials. 'n the utricle and saccule the hair cells areem"edded in an otoconial mem"rane hich contains particles of calcium car"onate.

These respond to changes in linear acceleration and the pull of gra!ity.

'mpulses are carried centrally "y the !esti"ular ner!e% and connections are made to the

spinal cord% cere"ellum and external ocular muscles.

The sensory ner!e supply of the ear is complex. The external ear is supplied "y the

auriculotemporal "ranch of the trigeminal ner!e *9+% and this supplies most of the

anterior half of the pinna and the external auditory meatus. The greater auricular ner!e

*:5%$+% together ith "ranches of the lesser occipital ner!e *:5+% supply the posterior

part of the pinna. The 9''th% ';th and ;th cranial ner!es also supply small sensory

"ranches to the external ear< this explains hy the !esicles of herpes =oster affecting

the 9''th ner!e appear in the concha *see -ig. /.5> later+. The middle ear is supplied"y the glossopharyngeal ner!e *';+.

This complicated and rich sensory inner!ation means that referred otalgia is common

and may originate from the normal area of distri"ution of any of the a"o!e ner!es. A

classic example is the referred otalgia caused "y a malignancy in the pyriform fossa of

the pharynx or a cancer of the larynx.

Anatomy of the ear

?Referred otalgia has many causes *e.g. cancer of the larynx+

?Middle ear is intimately related to the cranial ca!ity

?The 9llth ner!e has a tortuous course through the ear

:onditions of the external ear

:ongenital anomalies

:ongenital anomalies can range from total a"sence of the ear through to mild

cosmetic deformities such as tiny accessory auricles or s#in tags. External ear

anomalies can "e isolated or may "e associated ith middle ear deformity. The

external and middle ear originate from the first and second "ranchial arches% hereas

the cochlea is of neuroectodermal origin. This means that an indi!idual may ha!e no

pinna or ear canal "ut a normal cochlea may ell "e present. 'n these circumstances%

sound can "e transmitted from a hearing aid connected to an osteo integrated peg that

is screed into the mastoid "one. *Ta" /.0+

:hildren ho ha!e a significant deformity of the pinna *microtia+ can "e helped ithosteointegrated implants to hich a prosthetic ear is connected *-ig. /.$+. The ear

can "e unclipped prior to playing !iolent sport *e.g. rug"y+ and this unsettles the

opposition. @reauricular sinuses are a common congenital a"normality and

occasionally need excising "ecause of recurrent infections and discharge. The sinus

usually ends near the external canal "ut occasionally the trac# is !ery extensi!e and is

closely related to the facial ner!e% hich ma#es life exciting.

@rominent ears are a common deformity hich usually results from the a"sence of the

antihelix cur!e. 9arious cartilage scoring methods are a!aila"le to correct this

deformity.

Trauma

Trauma often affects the external ear. A haematoma of the pinna occurs hen "loodcollects "eteen the penchondrium and the cartilage. The cartilage recei!es its "lood

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metastasise to the parotid andFor nec# nodes and need radical surgical clearance. The

ear canal may "e in!aded "y tumours from the parotid and postnasal space carcinoma

hich creep( up the eustachian tu"e. All resecta"le malignant tumours of the ear are

treated primarily ith surgery ith or ithout the addition of radiation therapy.

The external ear

? titis externa responds to topical medication? nilateral otitis externa in a dia"etic may "e fatal

?Auricular haematoma needs a ro"ust incision% drainage and pressure dressing

?Thin# osteo integration for congenital malformations

:onditions of the middle ear *Ta" /.5+

:ongenital anomalies

:ongenital anomalies of the middle ear may "e isolated or may "e associated ith

other ear or general congenital deformities. There is a num"er of "ranchial arch

syndromes 6 for example @ierre Ro"in(s syndrome% craniofacial dysostosis% )on(s

syndrome and Treacher :ollins( syndrome. 'f there is an external ear a"normality% itshould raise suspicion of an underlying middle ear deformity. Middle ear deformity

can "e assessed "y high&resolution computerised tomography *:T+ scanning and% if

the inner ear is normal% reconstructi!e surgery of the middle ear can "e !ery

successful.

Trauma

Trauma to the middle ear can result in a perforated tympanic mem"rane *-ig. /.>a+.

Such perforations usually heal spontaneously *-ig. /.>"+. Trauma can result is

ossicular discontinuity and typically it is the incus that is displaced. 9arious

operations termed tympanoplasties( are a!aila"le to reconstruct the damaged

ossicular chain and repair the tympanic mem"rane if necessary.

'nflammatory disorders

The most common inflammatory condition of the middle ear is acute suppurati!e

otitis media. 't is extremely common in childhood and is characterised "y purulent

fluid in the middle ear. Mastoiditis may "e associated ith otitis media "ecause the

mastoid air cells connect freely ith the middle ear space. The tympanic mem"rane is

hyperemic and "ulges oing to pressure from the pus in the middle ear *-ig. /.0/+.

The child suffers extreme pain until the tympanic mem"rane "ursts. The most

common infecting organisms are Streptococcus pneumoniae and Haemophilus

influen=ae. Appropriate systemic anti"iotics should "e gi!en for 0/ days.

The incidence of acute mastoiditis has diminished ith the idespread use of

anti"iotics for otitis media. Sometimes% hoe!er% a child ill ha!e had a num"er ofcourses of anti"iotics% none of hich completely resol!es the middle ear infection. 'n

such cases the pain and selling "ehind the ear may not "e 3uite so apparent as in -ig.

/.00. 7hen mastoiditis is present% if the tympanic mem"rane can "e seen% there is

alays a sag in the posterior superior part of the drum. *:on!ersely% a normal

tympanic mem"rane excludes mastoiditis.+ Treatment re3uires hospital admission and

intensi!e parenteral anti"iotics. 'f this does not resol!e the infection 3uic#ly a cortical

mastoidectomy is re3uired% together ith a myringotomy.

Mastoiditis

? Se3uelae of acute otitis media

? May "e mas#ed "y anti"iotics

?Re3uires intensi!e anti"iotics andFor drainage

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titis media ith effusion *glue ear+ is !ery common ith the ma4ority of children

experiencing at least one episode of it during de!elopment. Many factors ha!e "een

implicated% although it is primarily thought to "e due to poor eustachian tu"e function.

xygen is continually "eing a"sor"ed "y the middle ear mucosa and this results in a

negati!e middle ear pressure unless the eustachian tu"e opens to replenish the air.

This negati!e middle ear pressure initially results in transudation of fluid into themiddle ear space *-ig. /.05+. 'f the hypoxia continues% a mucoid exudate is produced

"y the glands ithin the middle ear mucosa. This stic#y exudate is referred to as glue

ear(.

The folloing symptoms may "e associated ith glue ear2

?hearing impairment hich often fluctuates/ per cent of cases the operation is highly successful% "ut rare complica&

tions include se!ere sensorineural hearing loss and "alance distur"ance.

tosclerosis

?Ne "one formation in otic capsule

?Stapes fixation?ptions2

6 Reassurance>D+ Scott&Bron(s tolaryngology% Cth edn% 9ol. $% Butterorth&

Heinemann% xford.

,udman% H. and 7right% A. *eds+ *0>>+ Mason(s )iseases of the Ear% Cth edn%

Arnold% ,ondon.

9an Hassell% A.% Milford% :.A. and Bleach% N. *eds+ *0>>D+ perati!e

tolaryngology% Blac#ell Scientific% xford.