Acoustic Neuroma
There are ______ new acoustic neuroma tumors diagnosed each year per million persons in the US. AKA there are _______to_______ new cases each year.
10; 2000 to 3000
Acoustic neuroma symptoms usually occur between what ages?
30-60 years
What is an acoustic neuroma?
A benign, slow-growing tumor that develops on the 8th cranial nerve (vestibulocochlear nerve)
Describe the Middle Fossa Approach.
(Surgical Excision approach to manage acoustic neuromas) − Includes an incision above the ear that allows for the possibility of hearing preservation and for complete visualization of the entire IAC - It includes a craniotomy (bone is replaced) over the temporal lobe of the brain - This is preferred for small tumors in the IAC
Describe the etiology of an acoustic neuroma.
- Mostly of unknown cause 95% of the time (sporadic) - Due to a genetic basis 5% of the time (inherited). Specifically, malfunction on chromosome 22, which produces Melin, the protein produced that controls the growth of Schwann cells covering the nerve, thus causing an overproduction/accumulation of Schwann cells (the trigger of the malfunction is unknown)
What is Neurofibromatosis Type 2 (NF2)?
A genetic disorder of the nervous system that affects how nerve cells grow and form
A big red flag during conventional audiology of an acoustic neuroma is what?
An asymmetric SNHL
What is the 8th nerve responsible for?
Carrying information to the organs of hearing and balance to the brain
ABR response for a patient with an acoustic neuroma would show _______. Why is this true even for individuals with normal or mildly impaired hearing?
− Compromised components past Wave I - May have prolonged Wave V latency and interwave latency for I to V - Absence of later waves, total absence of entire test, non-replicable waveforms - Abnormally low V:I amplitude ratio - This is because the test reflects the activity of the auditory nerve and brainstem and is used to identify retrocochlear pathologies
What are rehabilitative options for facial nerve weakness post acoustic neuroma surgery?
− Eye care (artificial tears/lubricant) until function returns − If paralysis consists after 1 year, hypoglossal-facial nerve graft may be considered
What are the risks/complications of the Middle Fossa Approach?
− Facial nerve generally runs across a portion of the tumor, causing temporary post-operative paresis to be common - Risk of Dural laceration and avulsion w/ age - The possibility of post-operative trismus (aka lockjaw) due to manipulation and/or injury to the temporalis muscle - Temporal lobe traction, which leaves a chance of injury (hematoma, seizure)
Describe the prognosis (spread and/or likely course) of acoustic neuromas.
− Non-cancerous (benign) tumors that do not spread (metastasize) to other parts of the body but may continue growing and pressing on important structures of the skull − It is small, slow-growing tumors that my not need treatment
What are potential risks / complications of general surgery for Acoustic Neuroma removal?
− Post-operative disequilibrium is not uncommon (the degree depends on how much information was reaching the brainstem pre-surgery) − Tinnitus (may be eliminated, improved, worse or changed) − Facial function (varies according to tumor size and may be delayed) − Hearing (dependent on criteria for successful hearing conservation)
What are the risks/complications of the Retrosigmoid Approach (aka Suboccipital)?
− Retraction of the cerebellum, which is required for adequate visualization (may lead to postoperative edema, hematoma, infarction and bleeding) - Increased incidence of CSF leak - Greater chance of severe post-operative headache - Higher incidence of tumor reoccurrence or persistence
What two forms do acoustic neuromas occur in and what % of cases?
− Sporadic (unknown cause) 95% of the cases − Inherited (NF2 / malfunction on chromosome 22) 5% of cases
Describe the Retrosigmoid Approach (aka Suboccipital).
(Surgical Excision approach to manage acoustic neuromas) − Occurs through the skull behind the ear, - Can remove tumors of all sizes - Is preferred for tumors larger than 2.0cm - There is a possibility of hearing preservation
Describe the Translabyrinthe Approach.
(Surgical Excision approach to manage acoustic neuromas) − Incision behind the ear - Includes a craniectomy (permanent removal of mastoid bone and SCC's) - Can remove tumors of all sizes without retracting any portion of the brain - This is preferred for when a patient has no useful hearing or when the tumors are larger than 2.0 cm
What are the advantages of Stereotactic Surgery / Radiation therapy?
- Achieves good tumor control in about 2/3 of cases - Preserves hearing in 1/3 of cases for patients w/ Vestibular schwannomas related to NF2
This management approach of an acoustic neuroma is typically used for elderly patients w/ small tumors (especially if their hearing is good) and have medical conditions that may increase operation risks. It is also used for those who refuse surgery and when the tumor is on the side of an only hearing ear or seeing eye.
Careful Observation / "Watchful Waiting" Approach
What 2 separate nerves make up CN VIII and what information to they each carry?
Cochlear nerve (hearing) and vestibular nerve (balance)
For an individual with NF2, what is the primary event that causes acoustic neuromas?
Dysfunction of the NF2 gene (aka the tumor suppressor gene on chromosome 22), which usually produces a suppressor protein (Merlin), primarily regulates cell division. Without this protein, uncontrolled Schwann cell proliferation takes place
Acoustic reflexes for a patient with an acoustic neuroma would be _______
Elevated or absent
Gadolinium contrast is critical to use during this definitive diagnostic test. Explain why.
Gadolinium-enhanced MRI because a non-enhanced MRI can miss small tumors
What are some risk factors identified for acoustic neuromas?
Genetics (NF2) through autosomal dominant inheritance and radiation exposure during childhood
What are the risks of Stereotactic Radiosurgery / Radiation Therapy?
HL, facial weakness and balance problems; also may take weeks, months or years before effects of this procedure become evident
What are rehabilitative options for hearing loss post acoustic neuroma surgery?
Hearing aids, CROS HA, BAHA, CI
This is a canal of the temporal bone of the skull and carries the facial nerve and vestibulocochlear nerve from the IE to the brainstem
Internal auditory canal (IAC)
Can acoustic neuroma cause HF SNHL and/or LF SNHL, and which occurs most often?
It can cause both HF and LF SNHL, but HF SNHL occurs in 2/3 of patients
How is the basis for choosing a surgical excision approach made?
It varies based on the tumor size, status of hearing and the degree of surgeon experience
During an Otologist's evaluation of a patient presenting with symptoms of an acoustic neuroma, what may they do?
Make referrals to an audiologist and/or for radiologic imaging (MRI or CT); may use Gadolinium w/ MRI for better imaging results
What information does the facial nerve conduct?
Motion of the face on that side, taste from the front 2/3 of the tongue, and tear production of the lacrimal glands of the eye
What do Schwann cells produce and what does this substance allow?
Myelin; an efficient conduction of nerve impulses
This genetic disorder is characterized by bilateral acoustic neuromas.
Neurofibromatosis Type 2 (NF2)
Can ANs be transmitted through generations?
No
OAEs for a patient with an acoustic neuroma can be _______, depending on whether the cochlea is compromised or not
Normal or abnormal
The junction where the Schwann cells meet the Oligodendroglia cells is called what?
Obersteiner-Redlich Zone
The superior (SVN) and inferior vestibular nerve (IVN) located centrally (closer to the brainstem) are coated by __________, which have the same function as Schwann cells (to produce myelin)
Oligodendroglia
In NF2, individuals are born with what?
One defective Tumor Suppressor Gene; only one mutation in any Schwann cells
How many properly functioning Tumor Suppressor Genes are needed to keep a tumor from occurring?
Only one
Caloric responses for a patient with an acoustic neuroma would be _______
Reduced or absent (~50% associated w/ unilateral loss of this response)
What two surgical excision approaches allow for the possibility of hearing preservation?
Retrosigmoid Approach (Suboccipital) and Middle Fossa Approach
Which surgical excision approach is associated with a pathologic headache post-operatively and why?
Retrosigmoid Approach (Suboccipital) because you enter the skull behind the IE and retract the cerebellum for better visualization
The superior (SVN) and inferior vestibular nerve (IVN) located peripherally (closer to the IE) are coated by ________
Schwann Cells
Acoustic neuromas arise from ________ located near the __________.
Schwann cells; Obersteiner-Redlich Zone
What are rehabilitative options for vestibular rehabilitation post acoustic neuroma surgery?
Should begin weekly 1-2 months following discharge and should involve the surgeon
This management approach consists of delivering high doses of radiation precisely to the core of the tumor, without making an incision, to slow down / stop the tumor growth. Generally an option if the tumor is small or the patient is not a candidate for surgery; possibly for a residual tumor as well; it is a one-day treatment and the effect time is variable. A doctor (neurosurgeon) usually monitors progress
Stereotactic Radiosurgery aka Radiation Therapy
What is the first line of treatment for individuals with Sporadic Vestibular Schwannomas?
Stereotactic Radiotherapy / Radiation Therapy
Although generally slow-progressing, hearing loss can be ______ or ______ in 5-15% of patients due to the disruption of cochlear blood supply.
Sudden or fluctuating
This surgical excision approach is preferred for when patients have small tumors of the IAC and allows for both the possibility of hearing preservation and completely visualization of the IAC.
The Middle Fossa Approach
Which surgical excision approach has the possibility of hearing preservation and leads to a greater chance of severe post-operative headaches?
The Retrosigmoid Approach (Suboccipital)
Which surgical excision approach may leave you with complete hearing loss on the operated side and how?
The Translabyrinthe Approach because you are performing a craniectomy, which means you are removing the mastoid bone and SCC's permanently
This surgical excision approach is preferred for when patients have no useful hearing or when tumors are larger than 2.0cm.
The Translabyrinthine Approach
What is the issue with an acoustic neuroma and why?
The location b/c it can grow and expand, creating a lot of damage to functional structures located near CN VIII
For a sporadic AN, a change or mutation has to occur in ________to affect both Tumor Suppressor Genes before a tumor can form?
The same Schwann cell twice
What is the name of the two regions in the genetic makeup of Schwann cells prevent the formation of tumors? / The same genes that when mutated are responsible for acoustic neuromas arising?
Tumor Suppressor Genes
Acoustic neuromas are almost always uni- or bilateral?
Unilateral
What are the presenting symptoms of an acoustic neuroma?
Unilateral (asymmetrical), slow progressing SNHL, tinnitus (usually confined to affected ear), unsteadiness, vertigo, facial numbness, and headaches
When are inherited acoustic neuroma symptoms usually evident?
Usually at birth and almost always by teenage years
What are two other terms synonymous with acoustic neuroma?
Vestibular Schwannoma and Acoustic Neurilemoma
Most acoustic neuromas develop on what branch of the CN VIII?
Vestibular nerve branch
What are the 3 ways of managing acoustic neuromas?
− Careful observation / "watchful waiting" approach − Radiation Therapy aka Stereotactic Radiosurgery − Surgical Excision (Retrosigmoid (Suboccipital), Translabyrinthe, and Middle Fossa Approach)
What are the risks/complications of the Translabyrinthe Approach?
− Complete HL on operated size - Fat graft required from the abdomen - Can cause hematoma, bleeding and / or infection at the donor site - Can help prevent CSF leaf − The sigmoid sinus is vulnerable to injury - A high jugular bulb or anteriorly placed sigmoid sinus may compromise space, which would result in the need for another approach to be selected
