Session 7: Functional Anatomy and Disorders of the Ear Flashcards
Three parts of the ear.
External
Middle
Inner
Common symptoms and signs of ear disease.
Otalgia Discharge Hearing loss Tinnitus Vertigo Facial nerve palsy
What are the parts of the external ear?
Pinna and external auditory meatus
What is the external ear lined with?
Skin
Contents of the middle ear.
Air filled cavity containing the ossicles.
What is the middle ear lined with?
Pseudostratified columnar epithelium
What are the three ossicles?
Malleus Incus Stapes
What separates the external ear from the middle ear?
The tympanic membrane
Contents of the inner ear.
Cochlea (hearing) Semicircular canals (balance)
What is the inner ear filled with?
Fluid
How does the inner ear communicate with the middle ear?
Cochlea communicates with the stapes by vibration of the stapes leading to vibration of the fluid in the cochlea.
What else does middle ear communicate with?
The oropharynx
What allows the middle ear to communicate with the oropharynx?
The pharyngotympanic tube also called the eustachian tube.
Why is the eustachian tube important?
It allows air to equilibrate with atmospheric pressure to relieve the negative pressure that would otherwise build up.
What opens the eustachian tube?
E.g. swallowing and yawning
What nerves carry general sensation from ear?
Branches of cervical spinal nerves C2/C3 Vagus nerve Trigeminal nerve (auriculotemporal) Glossopharyngeal nerve (tympanic) Small contribution from facial nerve This can lead to referred pain.
Give examples of other pains that can lead to otalgia.
Tonsils and pharynx Larynx Oropharynx (CN IX) TMJ pain (CN Vc) As well as cancers.
Special sensory of ears (hearing and balance).
Vestibulocochlear nerve
How does the pinna and external auditory meatus differ?
The pinna has elastic cartilage The external auditory meatus is made of bone.
Explain Ramsey Hunt syndrome.
Shingles of facial nerve due to varicella zoster. This leads to facial palsy on one side and a rash in external ear.
What is perichondritis?
Inflammation of perichondrium in pinna of ear.
What is a pinna haematoma?
Accumulation of blood between cartilage and its overlying perichondrium.
What usually causes a pinna haematoma?
Secondary to blunt injury to the pinna common in contact sports.
Pathophysiology of pinna haematoma.
The perichondrium is stripped off the cartilage. The perichondrium has the blood supply and this deprives the cartilage of the blood supply. Instead blood builds up between these layers in a subperichondrial space. This also leads to pressure necrosis of the tissue.
How is pinna haematoma treated?
By drainage of the blood as well as cotton rolls on either side of the pinna to pinch the perichondrium and make it re-apposition of the two layers to each other.
What happens if the pinna haematoma isn’t treated?
Fibrosis of the ear and new asymmetrical cartilage develops to cause what is called a cauliflower deformity.
How long is the external acoustic meatus?
2.5 cm
What is the shape of the external ear?
Sigmoid shape
What serves as a barrier to foreign objects in the ear?
Hair Sebaceous glands Ceruminous glands The bony part lacks these glands and hairs
What is another purpose of the ceruminous glands?
To produce ear wax
Explain the self-cleaning function of the external acoustic meatus.
Desquamation and skin migration laterally off tympanic membrane out of canal by epithelial migration. Mixes with wax to shed out of the ear.
Common conditions involving external acoustic meatus.
Wax / Foreign bodies
Otitis externa
What is malignant otitis externa?
A rare serious potentially life threatening disease which happens to immunocompromised patients like diabetics.
Pseudomonas aeruginosa as pathogen
How will acute otitis media present looking at the tympanic membrane?
Bulging tympanic membrane
How will otitis media with effusion present looking at the tympanic membrane?
Retraction of the tympanic membrane and evidence of fluid in the inner ear.
What is a cholesteatoma?
A retraction of pars flaccida of the TM to form a sac or a pocket. This traps stratified squamous epithelium and keratin which proliferates to form a cholesteatoma.
What is a cholesteatoma usually secondary to?
Chronic eustachian tube dysfunction where there is negative pressure in the ear leading to pulling the tympanic membrane inwards.
Symptoms of cholesteatoma?
Painless
Often smelly otorrhea
Sometimes hearing loss
Why are cholesteatomas important to diagnose?
They are not malignant but will slowly grow and expand to have more serious consequences.
This is because of enzymatic bone destruction of e.g. ossicles, mastoid and petrous bone or the cochlea leading to hearing impairment or infection of the brain.
What are the ossicles connected via?
Synovial joints
What are the functions of the ossicles?
To amplify and relay vibration from the TM to the oval window of the cochlea.
What is the ossicle movement tampered by?
Two muscles:
Tensor tympani and stapedius.
What is the acoustic reflex?
Contraction of the tensor tympani and stapedius due to loud noise to protect hearing.
What is one of the most common causes of acquired hearing loss in young adults?
Otosclerosis
What is otosclerosis?
Fused articulations of the ossicles due to abnormal bone growth. Particularly between the base plate of stapes and oval window.
This leads to sound vibrations not beeing transmitted as effectively.
This leads to gradual usually bilateral conductive hearing loss.
Why does the middle ear get negative pressure in absence of eustachian tube?
Because the mucous membrane of middle ear continuously reabsorbs air in middle ear which causes negative pressure.
The eustachian tube allows for equilibration.
It also allows for ventilation and drainage of mucous from middle ear.
Explain otitis media with effusion.
What causes it?
Not an actual infection.
Due to eustachian tube dysfunction.
Explain the pathophysiology of otitis media with effusion.
Fluid and negative pressure builds up in the middle ear due to eustachian tube dysfunction.
This leads to decreased mobility of tympanic membrane and the ossicles and affects hearing.
How is otitis media with effusion treated?
Usually conservatively as it usually resolves spontaneously in 2-3 months.
Complications and treatment of otitis media with effusion if it doesn’t spontaneously resolve.
Impede speech, language development and school performance.
Grommets which is a tympanostomy tube to equilibrate the pressure.
Explain acute otitis media.
Acute middle ear infection which is more common in infants than adults.
Signs and symptoms of acute otitis media.
Otalgia (infants may pull or tug at ear)
Fever
Red and bulging TM and loss of normal landmarks
Is acute media otitis usually bacterial or viral?
Viral
If otitis media is bacterial what is the usual pathogen?
Streptococcus pneumoniae
or
Haemophilus influenzae
Why might infants suffer from acute otitis media more commonly than adults?
Easier passage for infection because the ET is shorter and straighter in infants.
The tube can block more easily as well leading to otitis media with effusion.
Complications of acute otitis media.
Tympanic membrane perforation
Facial nerve involvment because its close relationship to the middle ear cavity via the facial canal.
Two intrapetrous branhes run through the midle ear cavity which are the chorda tympani and the nerve to stapedius.
Mastoiditis and intracranial complications like meningitis, sigmoid sinus thrombosis or brain abscess.
What is mastoidits?
Infection in the mastoid air cells as the middle ear cavity communicates via mastoid antrum and the mastoid air cells.
This is a potential route of spread into the mastoid bone.
Presentation of mastoiditis.
Bulging ear and red inflamed mastoid process.
What can be found in the inner ear?
Vestibular apparatus (semicircular canals) and cochlea.
Function of the cochlea.
Converts fluid movement into action potentials in CN VIII to be perceived as sound
Function of the vestibular apparatus.
Converts fluid movement generated by position and rotation of head in to action potentials in CN VIII. This is perceived as position sense and balance.
What does disease of the inner ear most commonly present as?
Hearing loss due to sensorineural
Tinnitus
Disturbances balance and vertigo
Important structures of the cochlea.
Explain their functions.
Oval window which sets up the movements of the fluid in the cochlear duct.
Waves of fluid cause movement of special sensory cells known as stereocilia which generates action potentials in CN VIII.
What is the function of the round window?
To move out when the oval window is pushed in by transmission of sound via the stapes.
This is necessary for fluid vibrations in the cochlea.
Explain how we hear.
Pinna and EAC focuses and funnels sound waves towards the TM which starts to vibrate.
The vibration of the ossicles sets up vibrations in cochlear fluid.
These vibrations are sensed by stereocilia nerve cells in the cochlear duct in the part of the spiral organ of the corti.
The movement of the stereocilia in organ of Corti trigger action potentials in cochlear part of CN VIII.
Primary auditory cortex perceive this as sound.
Functions of the vestibular apparatus.
Three semicircular canals: Anterior, posterior and lateral.
They are fluid filled with specialised hair cells that generate action potentials when moved.
The fluid filled tubes contain sterecilia. When the fluid moves due to moving position or rotation of head the stereocilia bends. This generate action potential via CN VIII to the brain. This is perceived and maintain our sense of balance.
What are the parts of the vestibular apparatus.
The semicircular ducts, the saccule and utricle.
Explain presbycusis.
Inner ear pathology.
Presbycusis which is a sensorineural hearing loss associated with old age. This is both bilateral and gradual.
Explain benign paroxysmal positional vertigo.
Benign Paroxysmal Positional Vertigo or BPPV.
Inner ear pathology.
This causes vertigo only. Which are short-lived and triggered by movement of the head as small crystals become dislodged and cause vibration of fluid in the semicircular canals even when head is still and you’re not moving.
So the brain thinks you are moving but you aren’t. This leads to vertigo.
How can BPPV be treated and managed?
Dix-Hallpike and Epley manoeuvres.
Explain Meniere’s disease.
Inner ear pathology where there is both hearing loss and vertigo as well as tinnitus.
Aural fullness, nausea and vomiting.
The symptoms are longer lasting from 30 mins to 24 hrs.
There is recovery between episodes but hearing may gradually get worse.
Explain acute labrynthitis.
History of upper respiractory tract infection where there is involvement of all inner ear structures associated with hearing loss and tinnitus as well as vomiting and vertigo.
Explain acute vestibular neuronitis.
History of upper respiratory tract infection.
Usually no hearing disturbance or tinnitus but there is sudden onset of vomiting and severe vertigo.
How do you investigate a patient presenting with hearing loss?
History
Examination by inspection and palpation of external ear and otoscopy.
Gross hearing assessment.
Tuning forks tests (Weber’s and Rinne’s test)
What is conductive hearing loss?
Pathology involving the external or middle ear.
Give examples of conductive hearing loss.
Wax
Acute otitis media
Otitis media with effusion
Otosclerosis
Cholesteotoma
What is sensorineural hearing loss?
Pathology involving the inner ear structures (cochlea) or CN VIII.
Give examples of sensorineural hearing loss.
Presbyacusis
Noise-related hearing loss
Meniere’s Disease
Ototoxic medications
Acoustic neuroma
