Head And Neck Week 7 Flashcards
What are the functions of the ear? (broadly)
Hearing Balance
How can the ear be divided anatomically?
External Middle Internal
What structures is the external ear composed of?
Auricle/pinna External acoustic meatus (ear canal)
Describe the structure and function of the auricle
Composed of an irregularly shaped plate of elastic cartilage that is covered by thin skin Has several depressions and elevations Concha - deepest depression Elevated margin - helix Non cartilaginous lobule/lobe - consists of fibrous tissue, fat and blood vessels Tragus - tongue-like projection overlapping the opening of the external acoustic meatus
Arterial supply- posterior auricular and superficial temporal arteries
Nerves to skin - great auricular nerve - supplies back of ear/ medial surface and the posterior part of the lateral surface/front (helix, antihelix, lobule)
Auriculotemporal nerve - branch of CNV3 - skin of auricle - anterior to external acoustic meatus
Minor contributions to skin of concha and its eminence by vagus and facial nerves
Lymphatic drainage - lateral surface/front of superior half - superficial parotid lymph nodes, back/medial surface of superior half - mastoid lymph nodes and deep cervical lymph nodes, remainder - superficial cervical lymph nodes
Function - collect sound
Describe the structure and function of the external acoustic meatus
Canal that leads inward through the tympanic part of temporal bone from auricle to tympanic membrane - 2.5cm long
S shaped
Keratinised skin
Lateral third is cartilaginous and lined with skin that is continuous with the auricular skin, contains ceruminous and sebaceous glands in the subcutaneous tissue - producing cerumen (earwax) - self-cleaning function - only bit with hair - hair and wax aids in preventing objects entering the canal and desquamation and skin migration out of canal
Medial two thirds - bony and lined with thin skin that is continuous with external layer of tympanic membrane
Function - conduct sound to the tympanic membrane
Describe the structure and function of the tympanic membrane
1cm diameter
thin, oval semitransparent membrane at medial end of meatus
forms partition between external acoustic meatus and tympanic cavity of middle ear
covered with thin skin externally and mucous membrane of the middle ear internally
Is concave when viewed through an otoscope - shallow cone-like central depression - peak is the umbo
Superior to lateral process of malleus - membrane is thin - pars flaccida - lacks radial and circular fibres - forms lateral wall of superior recess of tympanic cavity
Remainder of membrane - pars tensa - contains radial and circular fibres
Function - Moves in response to air vibrations that pass to it through the external acoustic meatus
Transmitted by the ossicles through the middle ear to the internal ear
Nerve supply - external surface of tympanic membrane supplied by auriculotemporal nerve (branch of CN V3)
Some innervation by small auricular branch of vagus (CN X)
Internal surface is supplied by glosspharyngeal nerve (CNIX)
Describe the basic structure and contents of the middle ear
Tympanic cavity - narrow air-filled chamber in petrous part of temporal bone
Tympanic cavity proper (immediately behind tympanic membrane) and the epitympanic recess (superior to the tympanic membrane)
Connected anteromedially with the nasopharynx via the pharyngotympanic tube/eustachian tube
Connected posterosuperiorly with the mastoid cells through the mastoid antrum
Lined with mucous membrane that is continuous with the lining of the phayngotympanic tube, mastoid cells and mastoid antrum
Contents:
Auditory ossicles : Malleus, incus, stapes
Stapedius and tensor tympani
Chorda tympani (branch of CN VII)
Tympanic plexus of nerves
Describe the structure and function of the pharyngotympanic/eustachian tube
Connects tympanic cavity to nasopharynx - opens posterior to inferior nasal meatus
Posterolateral third is bony, remainder cartilaginous
Lined by mucous membrane that is continuous psoteriorly with that of the tympanic cavity and anteriorly with that of the nasopharynx
function - equalise pressure in the middle ear with the atmospheric pressure by allowing air to enter and leave the tympanic cavity - allowing free movement of the tympanic membrane - also important in ventilation and drainage of mucous from middle ear
Walls of cartilaginous part normally in apposition - must be actively opened - by expanding girth of the belly of levator veli palatini as it contracts longitudinally - pushes against one wall - tensor veli palatini pulls on the other wall - muscles of soft palate - “popping the eardrums” associated with yawning and swallowing
Arteries - ascending pharyngeal artery - branch of ECA, middle meningeal artery and artery of pterygoid canal - branches of maxillary artery
Veins - drain into pterygoid venous plexus
Lymphatic drainage to deep cervical lymph nodes
NErves - tympanic plexus - formed by fibres of the glossopharyngeal nerve - anteriorly also receives fibres from pterygopalatine ganglion
Describe the structure and function of the auditory ossicles
Form a mobile chain of small bones across teh tympanic cavity from tympanic membrane to the oval window - an oval opening on the labyrinthine wall of the tympanic cavity leading to the vestibule of the bony labyrinth
First bones to full ossify during development - mature at birth
bone from which they are formed is exceptionally dense/hard
covered with mucous membrane lining the tympanic cavity -
lack a surrounding layer of osteogenic periosteum
Malleus (hammer) - attaches to tympanic membrane - rounded superior head of the malleus lies in epitympanic recess and articulates with the incus - neck lies against pars flaccida and handle is embedded in the tympanic membrane with its tip at the umbo –> moves with the membrane - tendon of tensor tympani inserts into handle near neck - chorda tympani crosses medial surface of neck - functions as a lever
Incus (anvil) - located between malleus and the stapes and articulates with them - body and two limbs - body lies in epitympanic recess - long limb lies parallel to handle of malleus and its interior end articulates with stapes by the lenticular process (medial projection) - short limb connected by ligament to posterior wall of tympanic cavity
Stapes (stirrup) - smallest - head, two limbs and a base - head articulates with incus, base fits attached to margins of oval window on medial wall of tympanic cavity - smaller than tympanic membrane –> vibratory force is increased x10 compared to tympanic membrane –> therefore ossicles increase the force but decrease the amplitude of vibrations transmitted from tympanic membrane to internal ear
What is unusual about the ossicles compared to other bones of the body
lack a surrounding layer of osteogenic periosteum
Describe the muscles associated with the auditory ossicles
Two muscles dampen or resist movements of the auditory ossicles
Tensor tympani - short muscle that arises from the superior surface of the cartilaginous part of the eustachian tube, greater wing of sphenoid and petrous part of temporal bone - inserts into handle of malleus - pulls handle medially, tensing tympanic membrane and reducing amplitude of its oscillations–> prevents damage to internal ear when exposed to loud sounds - supplied by mandibular nerve
Stapedius - tiny muscle- inside pyramidal eminence (hollow, cone-shaped prominence on posterior wall of tympanic cavity) - tendon enters tympanic cavity through pinpoint foramen in apex of the eminence - inserts on neck of stapes - pulls stapes posteriorly and tilts its base in the oval window - tightening anular ligament and reducing oscillartory range - prevents excessive movement of stapes - suppled by branch of facial nerve
Describe the basic structure and function of the inner ear
In petrous part of temporal bone
Contains the vestibulocochlear organ - concerned with sound reception and balance
Membranous labyrinth - contains endolymph - suspended in the perilymph-filled bony labyrinth - by delicate filaments similar to filaments of arachnoid mater or by the substantial spiral ligament - doesnt float
Membranous labyrinth - series of communicating sacs and cuts that are suspended in the bony labyrinth - contains endolymph - watery fluid similar to intracellular fluid in composition - stimulates end organs for balance - consists of vestibular labyrinth (utricle and saccule sacs), semicircular ducts and cochlear labyrinth (cochlear duct)
Bony labyrinth - perilymph (like extracellular fluid) filled space surrounded by the otic capsule of the petrous temporal bone - stimulates end organs for hearing - series of cavities - cochlea, vestibule, semicircular canals
Describe the structure and function of the cochlea
Shell-shaped
Spiral canal begins at vestibule and makes 2.5 turns around bony core (modiolus - spongy bone - contains canals for blood vessels and cochlear nerve)
Contains the cochlea duct - concerned with hearing
Communicates with subarachnoid space superior to jugular foramen through cochlear aqueduct
Round window - separated from tympanic cavity by secondary tympanic membrane
Describe the structure and function of the vestibule
Small oval chamber (5mm long) contains utricle and saccule and parts of the balancing apparatus
Oval window on lateral wall - occuppied by base of stapes
Continuous with bony cochlea anteriorly, semicircular canals posteriorly and posterior cranial fossa through vestibular aqueduct - extends to posterior surface of petrous temporal bone - opens posterolateral to internal acoustic meatus - transmits endolymphatic duct and two small blood vessels
Describe the structure and function of the semicircular canals
Anterior, posterior, lateral
Communicate with vestibule of bony labyrinth - lying posterosuperior to the vestibule
Right angles to eachother - occupying three planes in space
Each forms approx 2/3 of a circle - approx 1.5mm in diameter - except at the bony ampulla swelling
Have 5 openings to vestibule because anterior and posterior canals have one limb common to both
Contain semicircular ducts within
What is the spiral ligament?
Spiral thickening of the periosteal lining of cochlear canal - secures cochlear duct to the spiral canal of the cochlea
Describe the structure of the vestibular labyrinth (membranous)
Semicircular ducts open into utricle through 5 openings
Utricle communicates with saccule via utriculosaccular duct - wheree endolymphatic duct arises
Saccule continuous with cochlear duct through ductus ruiniens
Utricle and saccule have specialised areas of sensory epithelium - maculae - hair cells - innervated by vestibular division of vestibulocochlear nerve - primary sensory neurons in vestibular ganglia in internal acoustic meatus
endolymphatic duct traverse vestibular aqueduct - emerges through bone of posterior cranial fossa - expands into pouch called endolymphatic sac - located under dura mater on posterior surface of petrous temporal bone - storage reservoir for excess endolymph
Describe the structure and function of the semicircular ducts
Each has an ampulla at one end containing sensory area - ampullary crest - sensors for recording movements of endolymph in ampulla resulting from rotation of head in plane of the duct - hairs of crests - stimulate primary sensory neurons- cell bodies in vestibular ganglia
Describe the structure and function of the cochlear duct
Spiral tube closed at one end - firmly suspended across canal between spiral ligament on the external wall of cochlear canal and osseus spiral lamina of the modiolus
Cochlear duct divides the spiral canal into two channels that are continuous at the apex of the cochlea at helicotrema - semilunar communication
Roof of duct - vestibular membrane
Floor of duct - basilar membrane plus outer edge of osseus spiral lamina
Receptor of auditory stimul - spiral organ of Corti - situated on basilar membrane - overlaid by tectorial membrane
Describe how sound is detected in the inner ear
Waves of hydraulic pressure created in perilymph of vestibule by vibrations of stapes - ascend to apex of cochlea via scala vestibuli - pass through helicotrema and back to base by scala tympani - vibrates secondary tympanic membrane in the round window - energy finally dissipated into the air of the tympanic cavity
Spiral organ of corti contains hair cells - tips in tectorial membrane - stimulated to respond by deformation of cochlear duct induced by hydraulic pressure waves in the perilymph - ascend and descend in surrounding scalae vestibuli and tympani
Describe the internal acoustic meatus
A narrow canal that runs laterally for approx 1 cm in the petrous pat of the temporal bone
Opening is in the posteromedial part of petrous temporal bone - in line with external acoustic meatus
Closed laterally by a thin perforated plate of bone that separates it from the internal ear - the facial nerve, vestibulocochlear nerve and blood vessels pass through this plate
Vestibulocochlear nerve divides near the lateral end of the internal acoustic meatus into two parts:
cochlear and vestibular nerve
What might trauma to the external ear cause and what are the consequences if this is left untreated?
Auricular haematoma - localised collection of blood between the perichondrium and auricular cartilage –> distorts contours of the auricle
As the haematoma enlarges it comprises the blood supply to the cartilage and causes pressure necrosis- if left untreated, fibrosis and new asymmetrical cartilage develops in the overlying skin, forming a deformed auricle (cauliflower or boxer’s ear)
How should an auricular haematoma be treated?
Aspiration of the blood
Measures to prevent reaccumulation and re-apposition of the two layers are necessary
How is an otoscopic examination performed and what information can be gained from it?
In adults - helix is grasped and pulled posterosuperiorly (up, back and out) to reduce the curvature of the external acoustic meatus and facilitate the insertion of the otoscope
In children and infants - meatus is short so care must be taken not to insert the otoscope too far - meatus is straightened by pulling the auricle inferoposteriorly
The examination provides information about the appearance of the external acoustic meatus and tympanic membrane - also provides a clue to tenderness, which can indicate inflammation of the auricular or meatus
Describe the normal/healthy appearance of the tympanic membrane
Translucent and pearly grey
Handle of malleus usually visible near the centre of the membrane (the umbo)
At the inferior end of the hand a cone of light is reflected from the otoscopes illuminator - ‘light reflex’ - radiates antero-inferior lymph
What is acute otitis externa ?
Inflammation of the external acoustic meatus
The infection often develops in swimmers who do not dry their meatus following swimming and/or use ear drops
May also be the result of bacterial infection of the skin lining the meatus
Individual complains of itching and pain in external ear, particularly when pulling or applying pressure to the auricle or tragus
What is otitis media, how can it be detected, why does it occur and what are the potential consequences if left untreated?
Infection of the middle ear
More common in children than adults - shorter Eustachian tube - easier for infection to pass from nasopharynx - more horizontal - easier blockage during drainage which predisposes to infection
Earache (otalgia) and bulging red tympanic membrane, indicating pus or fluid in the middle ear - individual may complain of ear “popping” - amber-coloured bloody fluid may be observed through the tympanic membrane
May also have a temperature
Often secondary to upper respiratory infections
Inflammation and swelling of the mucous membrane lining the tympanic cavity may cause partial or complete blockage of the pharyngotympanic tube - may produce impaired hearing if untreated due to scarring of the auditory ossicles, limiting their ability to move in response to sound
May cause perforation of the tympanic membrane, facial nerve involvement
Can have otitis media with effusion which is not an infection - due to Eustachian tube issues - causes negative pressure and fluid build up - predisposes to infection - can see straw colour fluid behind the tympanic membrane - affects movement of ossicles –> decreased hearing ability - dont normally complain of pain - can resolve spontaneously in 2-3 months or requires grommets (as above)
What are the typical causes of a perforated tympanic membrane?
Otitis media, foreign bodies in the external acoustic meatus, trauma, or excessive pressure (scuba diving)
What is the result of tympanic membrane rupturing?
One of the several causes of middle ear deafness
Minor ruptures often heal spontaneously
Large ruptures usually require surgical repair
What is a myringotomy, and how and why is it performed?
An incision in the posteroinferiorior tympanic membrane to release pus from a middle ear abscess
The inferior half of the membrane if much less vascular than the superior half and it avoids the chorda tympani and auditory ossicles
Given to people with chronic middle ear infections and followed with insertion of tympanostomy or pressure-equalisation tubes in the incision to enable drainage of effusion and pressure release
What is mastoiditis, what are the potential consequences and how is it treated?
Infection of the mastoid antrum and mastoid cells
Result from middle ear infection that causes inflammation of the mastoid process - epitympanic cavity communicates with mastoid air cells, which help equilibrate the pressure
Infection may spread superiorly into the middle cranial fossa through the petrosquamous fissure in children and cause osteomyelitis (bone infection) of the tegmen tympani
Mastoiditis is uncommon since antibiotics have been invented
IV antibiotics required
Operation for mastoiditis - surgeons concerned with avoiding the facial nerve
Can access the tympanic cavity through the mastoid antrum, only thin plate of bone removed in children but 15mm or more in adults
At present, most mastoidectomies are endaural (posterior wall of external acoustic meatus)
How does the pharyngotympanic tube become blocked and what is the consequence of this?
The tube is easily blocked by swelling of its mucous membrane, even as a result of mild infections (e.g. A cold) because the walls of the cartilaginous part are normally already in apposition
When occluded the residual air int he tympanic cavity is absorbed into the mucosal blood vessels, resulting in lower pressure in the tympanic cavity, retraction of the tympanic membrane and interference with its free movement
Hearing is affected
What is the pathogenesis behind hyperacusis?
Tympanic muscles have protective action - dampen large vibrations of the tympanic membrane resulting from large noises
Paralysis of the stapedius - from facial nerve lesions –> uninhibited movement of the stapes
Associated with excessive acuteness of hearing
How does motion sickness result?
Discordance between vestibular and visual stimulation
What are the three major symptoms of an injury to the peripheral auditory system?
Hearing loss (usually conductive), vertigo (dizziness - when involves semicircular ducts), tinnitus (buzzing or ringing - when injury is localised in the cochlear duct)
What are the two types of hearing loss?
Conductive hearing loss - results from anything in the external or middle ear that interferes with conduction of sound or movement of the oval or round windows - people with this type often speak with a soft voice because their own voice sounds louder tan background sounds - this may be improved surgically or by using a hearing aid
Sensorineural hearing loss - results from defects in the cochea, cochlear nerve, brainstem or cortical connections - cochlear implants are one approach employed to restore sound perception when the hair cells of the spiral organ have been damaged - sound received by small external microphone are transmitted to an implanted receiver that sends electrical impulses to the cochlea, stimulating the cochlear nerve - hearing remains crude but enables perception of rhythm and intensity of sounds
What is Meniere syndrome?
Excess endolymph production or blockage of the endolymphatic duct - characterised by recurrent attaches of tinnitus, hearing loss and vertigo
Also sense of pressure in the ear, distortion of sounds and sensitivity to noises
Characteristic sign is ballooning of the cochlear duct, utricle and saccule caused by an increase in endolymphatic volume
What causes high tone deafness?
Persistent exposure to excessively loud sounds causes degenerative changes int eh spiral organ - commonly occurs in workers who are exposed to loud noises and dont wear protective earmuffs (e.g. Jet engine workers)
What is otic barotrauma and who does it typically occur in?
Injury caused by an imbalance in pressure between the ambient air and air in the middle ear
Usually occurs in fliers and divers
What is Ramsay Hunt syndrome?
Shingles affecting the facial nerve
What are some rare but life threatening complications of otitis media?
Meningitis, sigmoid sinus thrombosis, brain abscess
What is a cholesteatoma?
A rare but serious complication of chronic/recurring ear infections and blocked eustachian tube
Retraction pocket forms adjacent to the tympanic membrane due to negative pressure
Skin cells get trapped, collect and continue to grow in this small pocket within the middle ear - slowly grows and expands - may erode into surrounding structures - including cranial cavity - not malignant
symptoms - painless otorrhoea to more serious neurological complications
What is benign paroxysmal positional vertigo?
Most common cause of vertigo
When move head in certain directions get dizzy
Thought to be caused by tiny solid fragments (otoconia) in the inner ear labyrinth
May get better on its own
Simple treatment of moving the head to various positions to shift the position of the fragments over a period of a few minutes can cure it in many cases
Name the four components of the temporal bone
Squamous
Petromastoid
Tympanic plate
Styloid process
Which part of the temporal bone is the external acoustic meatus in?
Tympanic plate - medially fuses with the petrous part
Where are the middle and inner ear situated?
Petromastoid part of temporal bone
Where is the carotid canal in relation to the middle and inner ear?
Runs in inferior border
How can a middle ear infection lead to a facial nerve lesion?
The facial canal is separated from the middle ear by a very thin piece of bone
In what position in the Eustachian tube normally?
Closed except when swallowing - palate muscles open
What might dense, white plaques on the tympanic membrane be due to ?
Tympanosclerosis
How can you tell what ear you are looking into (from an image of tympanic membrane)?
The cone of light should reflect anteroinferiorly - so in the right ear it is in the 4/5 o clock position and in the left it is in the 7/8 o clock position
What is an acoustic neuroma?
A benign schwann cell tumour of the vestibulocochlear nerve
Can cause hearing loss, tinitus, vertigo and facial nerve compression leading to facial parasthesia
How is the Rinne’s and Weber’s test performed and how are results interpreted?
Rinne’s:
Doctor strikes tuning fork and places on mastoid bone behind ear
When no longer hears the sound the patient signals the doctor
Doctor strikes fork next to ear canal
When no longer hears the sound the patient signals the doctor
Doctor records length of time patient hears each sound
Weber’s:
Doctor strikes tuning fork and places in middle of forehead
Patients notes where they can best hear the sound: right, left or both ears
Normal results are air conduction is > 2 bone conduction for the Rinne’s test and the sound is heard equally in both ears for the Weber’s
Conductive hearing loss BC > AC for Rinne’s test because there is a problem with the structures in the external and middle ear conducting the sound to the inner ear
and sound is heard better in the side of the pathology due to lack of background noises in that ear that usually dampen the sound of the bone conduction
Sensorineural hearing loss AC>BC but less than twice as big because the communication between the inner ear and the brain is damaged
sound is heard better in the side with no pathology because it is healthy :)
Describe the sensory nerve supply to the external ear and tympanic membrane
Auricle is supplied by the auriculotemporal nerve (CNV3) - anterior to external acoustic meatus - greater auricular nerve (C2/3) - back of ear and helix/antihelix, lobule - contributions from a small sensory branch of the facial nerve (Ramsay hunt syndrome) and auricular branch of the vagus nerve
Tympanic membrane - Auriculotemporal nerve external surface - some via auricular branch of vagus nerve
internal surface - glossopharyngeal nerve
Why do patients with a sore throats sometimes complain of ear pain?
Infection spreading via the Eustachian tube to the middle ear
And/Or
Shared sensory innervation of oropharynx and interior tympanic membrane - glossopharyngeal nerve
Why might a child with recurrent ear infections benefit from an adenoidectomy?
The adenoids located close to the Eustachian tube opening- disappear in adulthood - if swollen can block the Eustachian tube leading to recurrent ear infections of glue ear - removing them will allow the Eustachian tube to function normally
