Sense of hearing, CNVIII, middle ear disorders

Question 1

What is the function of the semi-circular canals?

Answer 1

Function is to detect displacement and acceleration of the head.

Question 2

What are the utricle and saccule

Answer 2

Otolith organs
One responsible for linear acceleration on the horizontal plane and other for acceleration in the vertical plane

Question 3

Where do the sensory neurones of vestibulocochlear organs have serve/supply and where are their cell bodies?

Answer 3

Serves the semi-circular canals, utricle and saccule, cochlear
Cell bodies found in the Vestibular/Scarpa’s ganglion and the modiolas of the cochlear

Question 4

What does the vestibulocochlear nerve split into?

Answer 4

Vestibular nerve - balance
Cochlear nerve - hearing

Question 5

Describe the course of CNVIII

Answer 5

2 parts of the nerve travel together from their sites of origin within the petrous part of the temporal bone, leave via the internal acoustic meatus (in the acousticofacial bundle). They cross the posterior cranial fossa to access the brain from its inferior surface at the ponto-medullary junction. Here they cross a CSF cistern of the cerebellopontine angle.

Question 6

What is the pontomedullary junction?

Answer 6

A natural groove on the inferior surface of the brain between the lower border of pons and the medulla

Question 7

Where is CNVIII vulnerable to certain pathological conditions?

Answer 7

Compression at level of cerebellopontine angle
Infection and inflammation
Neoplasms (vestibular schwannomas invade the substance of the brain and damage the nerve in the process)

Question 8

Which nerve is tested for hearing acuity?

Answer 8

Cochlear nevre

Question 9

What are the 2 recognised forms of deafness and how are they different?

Answer 9

Sensorineural deafness = damage to the nerve, usually irreversible and needs prostheses to fix
Conductive deafness = blockage of the auditory meatus - causes failure of pressure exertion on the tympanic membrane. Reversible by removal of blockage.

Question 10

What do the tests to differentiate between sensorineural and conductive deafness rely on?

Answer 10

Tests rely on air conduction being better than bone conduction. If air passages are blocked, air conduction is reduced = conductive deafness. If the nerve is affected, both modalities are reduced = sensorineural deafness.

Question 11

Is the Webber’s test for sensorineural or conductive deafness?

Answer 11

Conductive hearing loss or deafness

Question 12

Is the Rinnes test for sensorineural or conductive deafness?

Answer 12

Sensorineural hearing loss or deafness

Question 13

How is the Webber’s test performed and what are the results?

Answer 13

Tuning fork is struck and its base is placed at the vertex of the skull of a patient. Sound will be equal in both ears if there is no conductive loss. Sound will be hear louder on the side in which the ear is blocked.

Question 14

How do you conduct a rinnes test and what are the results?

Answer 14

Tuning fork is struck and its base is placed against the mastoid process. Strike fork again and bring it close to external meatus of the ear being tested. Ask patient if they can hear both times. If there is sensorineural hearing loss the patient will not be able to hear the vibrating fork in both tests.

Question 15

What will damage to the vestibular nerve cause?

Answer 15

Loss of balance, vertigo, nausea, nystagmus, impairment of caloric response

Question 16

What is acute otitis media?

Answer 16

Means acute infection of the middle ear. Occurs between the tympanic membrane and the inner ear. Usually products of an inflammatory response can clog up the middle ear to produce a build up and increase pressure, resulting in bulging of the tympanic membrane.

Question 17

What can happen in severe untreated cases of acute otitis media?

Answer 17

Tympanic membrane will rupture leading to drainage of pus through the external auditory meatus.

Question 18

Complications of acute otitis media?

Answer 18

Can lead to mastoiditis

Question 19

What can mastoiditis lead to?

Answer 19

Mastoiditis and AOM can invade the middle and posterior cranial fossae, leading to intracranial infection in the brain and death.

Question 20

What is otitis media with effusion/ serous/secretory otitis media?

Answer 20

Secretions from epithelium lining the middle ear accumulate together with the products of inflammation.

Question 21

What is Eustachian tube dysfunction?

Answer 21

Leads to a negative pressure in the middle ear cavity drawing the tympanic membrane in and reducing its ability to vibrate efficiently.

Question 22

What is glue ear characterised by?

Answer 22

Glue ear is characterised by adherence of tympanic membrane to ear ossicles. A bulging middle ear. The epithelium changes to become absorptive and absorbs all the fluid accumulating, leaving a super concentrate of mucous. Middle ear negative pressure results in the ossicles shrink wrapped in thick mucous and lining of tympanic membrane, providing a medium for bacteria to thrive in.

Question 23

How is glue ear treated?

Answer 23

Improving drainage via Eustachian tube via grommets to ventilate the middle ear.

Question 24

What are grommits?

Answer 24

Ventilation tubes applied through the tympanic membrane

Question 25

Complications of glue ear

Answer 25

Infections can spread into the middle cranial fossa via the temporal bone Infections can spread into posterior cranial fossa via epitympanic recess and mastoid antrum Infections can spread into sigmoid sinus via mastoid air cells In children loss of hearing can cause delayed maturation of brain and if untreated can lead to mental retardation

Question 26

How can the tympanic membrane get perforated?

Answer 26

Via direct trauma to the TM e.g., loud sounds Inflammation - myringitis Infections of the membrane

Question 27

How does TM repair after perforation?

Answer 27

But membrane can repair spontaneously as long as there is no infection

Question 28

Disorders of the ear ossicles

Answer 28

Synovial joints between the ossicles can become rigid due to calcification Osteosclerosis is the fusing of the stapes to the oval window, resulting in dampened movements of the ossicles (hence, hearing problems).