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Neurosurgery > Hearing > Flashcards

Hearing Flashcards

1
Q

What is sound?

A

vibration of air molecules from a wave like diffusion form a special source
Hight of wave = loudness

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2
Q

How does decibel work?

A

BD is log scale, change from 0 to 30 is an increase in 1000 times loudness

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3
Q

What frequency and loudness is normal speech?

A

Normal speaking is between 50-70 bd and between 100-4000 (k) hz

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4
Q

Anatomy of the outer ear

A

In external we have the auricle (visible ear) with an external meatus (the ear canal). The tympanum is the ear drum (the beginning of the middle ear)

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5
Q

Anatomy of the middle ear

A

The tympanum is the ear drum (the beginning of the middle ear) with the ossicles (consists of the malleus, indicus and the staple). You have your TheEustachian tube(it is a small passageway that connects your throat to your middleear)

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6
Q

how is sound created in the inner ear?

A

The stapes push on the oval window, which is the “opening” to the scala vestibuli chamber of the cochlear. This creates waves in the perilymph, that can move the basilar membrane. The basilar membrane is the most stiff at the base, which is why we need a high frequency to stimulate the membrane. The movement of the basilar membrane activates the inner hair cells.
When the basilar membrane moves, endolymph is rushed through the space between the hair cells and the tectorial membrane. This causes the hair cells to be bend towards the tectorial membrane. If the stereocilia are bend towards the kinocilia, it opens up the channels, which allows the K+ from the endolymph in. This causes the hair cells to release glutamate. This depolarizes the next cell and sense signals through the cohlear nerve.

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7
Q

Pitch and frequency

A

pitch depends on frequency - the basilar membrane responds to different frequencies in waves, which is translated into a different pitches.

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8
Q

inner hair cells

A

Are primarily responsible for sound (95%) and are only in one row in the scala media. The inner hair cells have stereocilia and kinocilia.

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9
Q

Outer hair cells

A

are in rows of 3 at the scala media - helps modualte sound captures by the inner hair cells.

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10
Q

Endolymp

A

in the scala media, high in K+ and low in Na+

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11
Q

Perilymph

A

In the scala vestibuli (upper compartment of the cochlear) and the scala tympani. Rich in Na+ and low in K+.

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12
Q

The 3 compartments of the cochlear

A

Scala vestibuli, scala media and scala tympani

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13
Q

What 2 mechanisms are important for the liquid in the cochlear being moved?

A

(1) changes from the eardrum to oval window and (2) the higher pressure per unit at the oval window

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14
Q

How do we see transduction in the cochlear?

A

Transduction: the process by which the ear converts sound waves into electric impulses
We see this by the inner hair cells opening their channels based on being pushed towards the kinocillium by pressing up on the tectorial membrane. Here we transform the waves in the liquid to the electrical signal created in the hair cells by glutamate release.

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15
Q

TheEustachian tube

A

a small passageway that connects your throat to your middleear

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16
Q

Frequency of AP in the cochlear never correlates with?

A

Loudness (DB)

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17
Q

helicotrema

A

Where the scala vestibuli and scala tympanic meet (where the basilar membrane is the most flexible and is activated by the lowest frequency sounds)

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18
Q

the ganglion spriale

A

The bipolar neurons that recive the gulatemate input form hair cells in the organ of corti. Has both efferent and afferent parts and signal to the cochlear nerve.

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19
Q

Auditory tract (afferent)

A

The inner and outer hair cell activation leads to the Nervus vestibulocochlearis (Cranial nerve 8), which projects to the cochlear nuclei in the brainstem. The signal crosses over and goes up the lateral lemniscus to the inferior colliculus, then to the corpora geniculate medial (medial geniculate nucleus) in the thalamus and then to the primary auditory cortex, which is tonotopically organized.

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20
Q

cochlear nucleus

A

Receives input from the cranial nerve 8 and is tonotopically organized. The cochlear nuclear complex is the first integrative, or processing, stage in the auditory system

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21
Q

inferior colliculus

A

Placed in the midbrain and receives signals from the lateral lemniscus. The inferior colliculus is important for analyzing the frequency.

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22
Q

Efferent signaling to the auditory tracts

A

From the olivary to the hair cells and ear muscles. Causes hyperpolarization and highlight important signals, active listening and help absorb small frequency ranges.

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23
Q

Semicircular canals

A

Semicircular canals are filled with endolymph and they have ampulla with hair cells what has stereocilia, which is important for the transduction. Works similarly to the inner auditory organ and are important for angular acceleration, where the otolith organs linear acceleration. Tonic signaling is either up or down regulated by movement (stereocilia bending away from the kinocilia decreases it). This changes the rate of NT release.

24
Q

Explain the Vestibular tract

A

vestibular system –> Vestibularnuclear complex (4 compartments) —> vestiboluspinal tract. The lateral part is for lower limbs and the medial for trunk and neck innervation (medial activates proximal)

25
Q

Vestibular schwannoma

A

A benign Schwanncell tumor in the Internal auditory meatus and cerebellopontine angle

26
Q

incidence and ago of those with schwannomas

A

20/1 mio and 40-60. 4% has genetic disposition through neurofibromatosis type 2

27
Q

Symptoms of schwannomas

A

Symptoms: hypoacusis (A hearing impairment associated with a deficiency in the peripheral neurosensory or conductive organs of hearing), Tinnitus, lack of balance, pressure in the ear
Rare: headaches, the affection of the intermediate, facial, trigeminal, abducens or the causal cranial nerves (can have problems with swelling.

28
Q

How to diagnose a Vestibular schwannoma

A

Tone and speech audiometry - testing what tones the patient can hear and what frequencies of speech (the last part is often impaired)

using electrophysiology to measure auditory brainstem responses (how the brainstem responds to different frequencies - often it doesn’t perceive high frequencies).

You can also see the tumor on an MRI scan (gold standard)

29
Q

Weber test

A

You need to know what ear is affected:
you place a tuning fork on the top of a patients head. A normal Weber test has a patient reporting the sound heard equally in both sides. In an affected patient, if the defective ear hears the Weber tuning fork louder, the finding indicates a conductive hearing loss in the defective ear. Also in the affected patient, if the normal ear hears the tuning fork sound better, there is sensorineural hearing loss on the other (defective) ear.

30
Q

Rinne test

A

The Rinne test is performed by placing a 512 Hz vibrating tuning fork against the patient’s mastoid bone and asking the patient to tell you when the sound is no longer heard. Once the patient signals they can’t hear it, the still vibrating tuning fork is then placed 1–2 cm from the auditory canal. The patient is then asked again to indicate when they are no longer able to hear the tuning fork. If the patient is not able to hear the tuning fork after it is moved from the mastoid to the pinna, it means that their bone conduction is greater than their air conduction (BC>AC). This indicates there is something inhibiting the passage of sound waves from the ear canal, through the middle ear apparatus and into the cochlea (i.e., there is a conductive hearing loss).

31
Q

The 3 therapy types of Vestibular schwannoma

A

Watch & Wait, radiatio, and surgery

32
Q

schwannoma: Watch & Wait

A

schwannoma therapy
For old patients and those with small tumors, where we limited symptoms and high risk surgery.
Patients get MRI once a year to look at the tumor
25-68% hearing preservation

33
Q

schwannoma: Radiatio

A

schwannoma therapy
for older patients, for those with smaller or residual tumors. Tumor could develop further
51-93% hearing preservation

34
Q

Swannoma: Surgery

A

schwannoma therapy
For all tumors, but not old/ill patients
aim is to “cure” by cutting tumor and maintaining function
51-88% hearing preservation
You cur behind the ear, burr hold in cranium, open dura, go along temporal bone, lift away cerebellum, and then find the tumor behind the cranial nerve. The patient is fixed

35
Q

ABR monitoring

A

The first 5 waves are important. They represent the (1) cranial nerve 8, (2) the cochlear nucleus, (3) the superior olivary, (4) the lateral meniscus and (5) the inferior colliculus.
If the 5 waves are there in tact, the auditory path is intact and the patient will hear after surgery

36
Q

ABR classification according Hannover principles

A

if wave 1, 3 & 5 are there, it’s a ABR 1, when the latency is longer it’s class 2 (ABR2), if wave 5 is missing, it’s class 3, if there is only one wave it’s class 4 and no waves = class 5

37
Q

Neurofibromatosis and types

A

Autosomal dominant genetic disorder

Types:

- Neurofibromatosis type 1: Morbus Recklinghausen
- Neurofibromatosis type 2
- Schwannomatosis
38
Q

Diagnosis criteria for Neurofibromatosis type 2

A

Main criteria is bilateral Vestibular schwannoma but there is an additional criteria for extra tumors. the extra tumors can be anywhere in the body.

39
Q

Genetic background for Neurofibromatosis type 2

A

Mutation in the the neurofibromatosis type 2 gene leads to the Merlin protein, which is tumor suppressing, to be dysfunctional

40
Q

2 major reasons for deafness

A

lesions in the cholera or of the auditory nerve

this might be caused by inborn malfunctions, infections, trauma, tumors or hemorrhage

41
Q

Cochlear implant vs. auditory brainstem implant

A

The most popular implant is the cochlear implant, which helps to restore hearing in diseases in the cochlear, when we have a functioning auditory nerve. If this is not the case, we need an implant on the brainstem (auditory brainstem implant). Expected performance with ABI should be better than with Hearing Aid or Cochlea Implant .

42
Q

Pre-operative test for an ABI

A

promontory test might prove the presence and conductivity of the auditory nerve. We use an electrode to the cochlear or an ear-channel electrode. The patient might respond with hearing sensation and we should be able to measure the evoked potentials

43
Q

ABI components

A

It has a coil, electrode, receiver and speech processor

External components: speech processor and receiver is behind the ear and is fixed with a magnet, where it’s coupled to the coil with the electrode under the skin.
The coil is delivering the electric stimulation program and the electrode pattern. This electrode pattern is arranged of 12-22 platinum electric contacts

44
Q

Bilateral deafness by age

A

At infant-ness, most cases are inborn cases with a missing auditory nerve or each side or a malfunctioning cochlear. In adolescent and advanced age, trauma or tumors might be the cause of bilateral deafness.

45
Q

Who can get auditory rehabilitation?

A

Patients with bilateral deafness or bilateral deafness expected soon, patients with unilateral declining function in their last hearing ear
However, they need to be stable if they’re NFT2 patients.
It’s mandatory if patients have tumors that threaten the vision

46
Q

Pre-surgical steps to get a ABI

A

All patients receive a genomic testing, evaluation of their evoked response audiometry and promontory tests. All other cranial nerves are well documented and all patients receive multiple interviews with clear explanations of the surgical process. The information that the decision to implant the ABI can only be taken during surgery.

47
Q

ABI surgery detail

A

On the day of surgery: before starting the operation, the head must be fixed in order to ensure absolute precision and surgery. The multimodality, neurophysiological monitoring is set up with auditory stimuli and electrodes of the tongue movements, swallowing e.g. - all cranial nerves assessed.
Before the ABI is placed, large tumors needs to be removed. We can dissect the tumors away from the brainstem by preserving the brainstem and remove the tumor from the nerves.

After tumors resection, the brainstem is exposed. Exactly between the 7th (facial) and the 9th (glossopharyngeal) nerves. Between their exit zones, we find the interzone for the 8th (auditory) nerve. Here the auditory nucleus dorsalis is to be expected.

During the phase of test-stimulation of the brainstem, we wish to avoid side effect stimulation of the long tracts and of the caudal or facial nerves. Secondly, we wish to evoke brainstem auditory responses. Particularly 3rd and 5th components

After successful test stimulation, the final electrode is inserted. Electric ABI is continuously controlled. If there is not full electrode contact, the electrode plate is adjusted.

48
Q

Testing after ABI placement

A

The post-operative testing of the hearing at various frequencies (500 hz to 4000 hz), is looked at to ensure that the patient can hear at all frequencies.

49
Q

ABI improvements over the last 20 years

A

before, the patient had to carry the receiver in his pocket. On the right side, we see a processor only behind the ear (no extra box).

50
Q

The consonant test

A

A test where participants discriminate consonants. Is preformed 6 months after ABI placement, where we test ability to read lips, just listen or both. Overall, the “both” condition yielded the best results.

51
Q

HSM testing

A

testing natural speech for sentences in those with ABI (blinded experiment). If you understand 30% of a sentence, you will understand 30-40% more with lipreading. 13/19 had an HSM over 30% –> our technology has advanced a lot

52
Q

What do we test in those with Inborn Lack of VIIIth Nerve?

A

If the auditory system is functioning. This requires surgery to place an electrode on the entry of the 8th nerve, where we should see wave 3-5 on the E-ABR. If yes, we can insert an ABI

53
Q

How many percent choose permanent deafness over ABIs?

A

2-3% - they are afraid to be disappointed by the results

54
Q

What emotional effect are often see in patients with permanent deafness?

A
  • They show more signs of psychological distress,
  • They show more distress than blind patients,
  • They report more oncological distress than hearing patients/ implant patients.
55
Q

Functional outcome of an ABI depends on?

A
  • the integrity of the cochlear nucleus
  • the exact implant placing (mapping is mandatory),
  • the professional and long-term adaptation of the stimulation programme.
56
Q

Can NF2 tumors affect ABIs?

A

Yes! But recurrence surgery has a good potential for re-establishing auditory function

Neurosurgery (10 decks)

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