Cranial Nerve 8

Last Updated: 03/28/17

Index

  1. Vestibular Schwannoma
  2. Damage to the Facial Nerve: CN7
  3. NF2 and no VS Development
  4. Tumor Management
    • Microsurgery
    • Radiation:
      Radiosurgery / Radiation Therapy
    • Clinical Trial:
      Molecular Target Tumor Treatments
      (Tumor Suppressors)
    • Hearing Implants
Monocystic, schwannoma, Polycystic, typical, Multi-lobulated










Also See

  1. Hearing Implants
  2. Additional Hearing Options
  3. Balance Issues
  4. NF Timeline

Vestibulocochlear Nerve

Hearing, Balance and Vestibular Schwannoma

Cranial Nerve 8 (CN8), is the Vestibulocochlear Nerve. As is the case with all cranial nerves there are two, one branches from the left side of the Brainstem (region cranial nerves start, from Medulla Oblongata and Pons) and one on the right side of the Brainstem. After a short distance from the Brainstem, the Vestibulocochlear Nerve splits to become the Vestibular Nerve (balance nerve) and the Cochlear Nerve (hearing nerve), as it extends towards the Inner Ear. Loss of function on CN8 for one side of the head would leave an individual with Single Sided Deafness (SSD) and some balance issues. Loss of function of left and right of the Vestibulocochlear Nerve results in severe balance issues and deafness.

A battle everyone born with Neurofibromatosis Type 2 (NF2) is likely to face, some earlier than others, is growth and issues of some level from one Vestibular Schwannoma (VS), on one side of the brain, or Bilateral Vestibular Schwannoma (Bilateral VS). NF2, does not always result in other tumors in the; brain, spinal cord and potentially other parts of the body. Bilateral VS is a fairly common issue consistent with individuals having Inherited NF2. When these VS may start to grow, and the rate of growth, is primarily dependent on an individual's exact NF2 mutation, but individual environment variables may increase the growth rate. Reason for growth other than genetics is topic for debate by researchers.

The name Vestibular Schwannoma (VS) is derived from the location and tumor type; A) The tumor growth from typically the Vestibular Nerve, B) the tumor is a Schwannoma and C) the term Bilateral means growth on both the left and right side of the head. Due to proximity to the brainstem, as VS grow larger they can also; A) damage the Facial Nerve (CN7), B) like any other tumor that may grow in the skull can be life threatening based on tumor size, exact location and growth rate, and C) sometimes result in memory or concentration issues.

Important to Note: Tumor growth can cause damage on part of the branch and potentially not damage the Cochlear Nerve portion (hearing) completely. Even complete damage to one or both Vestibular Nerves will not result in complete loss of mobility, it will only result in balance issues at worse, requiring only cane or walker, which can improve on its own in time, with good results from Vestibular Rehabilitation Therapy (VRT). Also, individuals with even Bilateral Vestibular Nerve damage will stand and take their first steps again after both nerves are completely broken (left and right). Unfortunately, it seems to take a little longer for people who develop VS but do not have NF2.

Read further to learn more about:

  1. Vestibular Schwannoma
  2. Damage to the Facial Nerve: CN7
  3. NF2 and no VS Development
  4. Tumor Management
    • Microsurgery
    • Radiosurgery or Radiation
    • Clinical Trial: Molecular Target Tumor Treatments (Tumor Inhibitor)
    • Hearing Implants
.

1. Vestibular Schwannoma

When a person is born with the disorder NF2 they have either a missing or broken tumor suppressor gene called NF2 in some or all of their body. As a result, they cannot make the protein MERLIN (Moesin-Ezrin-Radixin-Like Protein) which can cause tumor growth, particularly Vestibular Schwannoma.

It is argued that up to 99% of people with NF2 will develop Bilateral VS, but recent research suggests the rate may be lower. It is also important to understand that growth of a VS does not guarantee complete hearing loss. Size of the tumor is not the determination factor of when hearing will be lost and tumors can stop growing for long periods of time in years before continuing to grow again.

VS are very common tumors to grow, the majority of people who develop them do not have NF2. There are two different growth patterns of these massed, what we will simply call 1) Typical and 2) Multi-lobular. The Typical VS is simply an overgrowth of a Schwann Cell inside the nerve cell. The Multi-lobular seems to be a cluster of Schwann Cells, which NF2 surgeons have noted as look and acts similar to a bundle of grapes in surgery. The Multi-lobular might be from one nerve or a combination from the; Cochlear, Vestibular and / or Facial Nerve. An individual with VS but does not have NF2 would likely be just a Typical, the Schwann Cell overgrowth. An individual with NF2 can have growth of either type.

This is important for doctors who do surgery resection or radiation should know because poor imaging scan example of CT instead of MRI, or low strength MRI may not have the clarity to display and could result in wrong choice of treatment.

Vestibular Schwannoma (VS) are sometimes called Acoustic Neuroma (AN). AN, simply means acoustic tumor, but Vestibular Schwannoma was determined by the scientific community to be technically more accurate.


1.1. Tinnitus

Tinnitus is a phantom sound people start to hear when hearing loss develops. Once it starts, it does not go completely away, even if a person experiences complete hearing loss. However, things can be done to make it manageable or worse. For people with NF2, development of random Tinnitus is an indicator that the Cochlear Nerve has some level of damage.  


1.2. The Middle Ear

The contents of the Middle Ear include the three smallest bones in the body. These bones sit just inside of the Tympanic Membrane (Eardrum). This set of bones called the Ossicles, include:

  • Malleus (Hammer)
  • Incus (Anvil)
  • Staples (Stirrup)

Hearing loss in the general population; is frequently a result of rupturing the Eardrum or one of the three tiny bones and easily corrected with sound amplification or a Cochlear Implant.

Damage to the Middle Ear is not the reason for hearing loss for NF2.


1.3. The Inner Ear

  • CN8 - Vestibulocochlear Nerve: As this Vestibulocochlear Nerve leaves the center of the brain it splits in half to become the Vestibular Nerve and the Cochlear Nerve.
  • Cochlear Nerve: The Cochlear Nerve (sometimes referred to as the Auditory Nerve), branches off of CN8, goes to the Cochlea (Spinal Ganglion) and is the nerve specifically for hearing.
  • Vestibular Nerve: This nerve branches off of CN8, goes to the Vestibule and the Semicircular Canals, which are for balance and orientation.
  • Membranous Ampulla (Balance Glands): Body movement is sent through the Posterior, Superior and Lateral Canals Semicircular Canals into the Ampullae glands at the end of each canal. This information is then sent to the Vestibular Nerve.

2. Damage to the Facial Nerve: CN7

Vestibular Schwannoma can also damage Cranial Nerve 7, the Facial Nerve, due to proximity of the Vestibular Nerve. Both nerves extend from the brain stem, the center of the brain, very close to each other and as they extend to the side of the head damage to one can easily result in damage to the other.

For individuals with NF2, medical treatments are often necessary because a tumor is life threatening, but other treatments are necessary to help individuals maintain a normal quality of life, an example of that would be for the prevention of hearing loss. Since there is currently no treatment to destroy all tumors developed as a result of NF2, medical treatment is only a matter of tumor management.

The facial nerve can easily be broken or otherwise weakened, during treatment management of VS. There are different treatment techniques for different approaches to remove or manage tumors based on location, size, and tumor shape, rate of growth, age height, weight and general health. Treatments might include different surgical approaches for removal of a tumor, some form of radiation treatment, or chemotherapy.

Damage to the Facial Nerve can happen as a result of:

  • Growth of a Vestibular Schwannoma
  • Surgery / Microsurgery of a Vestibular Schwannoma
  • Radiation Treatment of a Vestibular Schwannoma
  • Growth of a Facal Schwannoma (Schwannoma on CN7)

3. NF2 and no VS Development

Individuals, who are told they have NF2, but do not develop VS, may in fact have NF3, also known as Schwannomatosis (SWN). NF3 is similar to NF2, except individuals with NF3 do not develop VS. NF2 is not always found in genetic tests and if a person is not confirmed in a genetic test, it is possibly they have NF3. Genetic confirmation of NF3 was not 100% accurate until after 2013 when it was realized that 2 different proteins can cause NF3. Since NF2 and NF3 are genetically different and do develop different issues over time, individuals who do not have VS and were told they have NF2 prior to 2014 should consider having a new genetic test done. See NF Timeline


4. Tumor Management

The only tumor management for NF2 is treatment of one tumor at a time. Surgery to remove a tumor over Radiation Treatment or Radiotherapy treatments is the ideal option, with the most important thing in consideration is surgeon experience with NF2 treatments and assumption of second opinions.

Regardless of treatment, tumors can form on the same nerve after a treatment is done and a tumor radiated is at higher risk of continued growing again a few years later.

3.1. Microsurgery

Microsurgery is the only way to stop a tumor from further damage completely, but a new one can grow back in other areas of the nerve. These surgeries can be difficult to recover from. There are different surgical approaches that increase the chance of best results.

If a tumor later grows in what appears to be the same place, it is impossible to determine if the new tumor is in a slightly different location or the same location as the tumor that was initially removed.


3.2. Radiation: Radiosurgery or Radiation Therapy

Radiosurgery or Radiation Therapy works on some people and some tumors but can take months to know for certain if it works and can result in the delay of valuable time. While there could be other side effects including tumor swelling shortly after treatment before a tumor might stop growing or shrink, it is the easiest treatment to recover from short term and if it works can stop the growth of a tumor for many years. It has harder to recover long term side effects than resection (surgery to remove a tumor).

The concern is that Radiation or Radiotherapy treatments are less likely to work long term in people with NF2 and can in fact cause more damage. [Ohio Gathering, Dr. A.]


3.3. Clinical Trial: Chemotherapies' / Molecular Target Tumor Treatments (Tumor Inhibitors)

Medications that are Tumor Inhibitors / Tumor Suppressors, more accurately Chemotherapies' / Molecular Target Tumor Treatments have been in trials for some time but none has been proven to be 100% effective on shrinking or stopping growth in everyone with NF2. New treatments are being developed and should be watched. Due to these treatments many people are finding themselves able to manage hearing with a Cochlear Implant for increasingly longer periods of times.


3.4. Hearing Implants

Cochlear Devices are Hearing Implants like the Auditory Brainstem Implant can aid in hearing loss when all else fails, there is more than one Cochlear Devices that might be of help as well and sound amplifications options that can aid in even better sound with these devices.


3.5. Additional NF2 Tumor Management Options

It is important to know the advantages and disadvantages of all of the NF2 Tumor Management options available for informed medical decisions.

While the most effective treatments to date are surgical and radiation, one of the problems with both microsurgery to remove a tumor and radiation to stop growth is that they often damages the facial nerve, clinical trials are underway for different tumor cytostatic or cytotoxic agents that can prevent or delay the need for either treatment for some time.

NF2 Information and Services pages are meant to be shared with doctors and others with NF2 in hopes to help more people.

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