Acoustic Neuroma

An Acoustic Neuroma also known as Vestibular Schwannoma is a slow growing tumor that develops on the cranial nerve that connects the ear to the brain. Cranial nerves are those nerves that arise directly from the brain. An acoustic Neuroma is a benign (non-cancerous) growth that forms on the sheath covering of the eighth cranial nerve called vestibulocochlear nerve. The eighth cranial nerve has two divisions, the vestibular nerve that controls the balance and the cochlear nerve that takes care of the hearing function. These two nerves are lined by Schwann cells and acoustic neuroma occurs when there is a large production of Schwann cells forming into a tumor.

Schwannoma that occurs in other peripheral nerves are largely benign unless it is a Neurofibrosarcoma - a malignant form of cancer.

Symptoms of acoustic neuroma

• The early signs of the condition include hearing impairment in the affected ear and the balancing difficulties. Since nerves of eighth cranial are responsible for hearing and balance, the problems related to these functions are the first to surface in the initial stages of acoustic neuroma. Patient may also feel heavy or fullness in the affected ear. Hearing loss either progressively or suddenly in the affected ear is the most obvious symptom of acoustic neuroma.
  
  
• Tinnitus is an ear condition where the patient experiences constant buzzing or ringing sounds in the ear. Though Tinnitus is a common symptom associated with acoustic neuroma, not all the cases will develop this symptom. It is also to be noted that all those who experience tinnitus do not have tumor growing on the ear nerve.
  
  
• Vertigo and unsteadiness is the common symptom with acoustic neuroma.
  
  
• When the tumor becomes large, it may compress the brainstem and result in headaches.
  
  
• Though not very common, acoustic neuroma may cause facial numbness and paralysis. Large tumors may compress the fifth cranial nerve (facial nerve) called trigeminal nerve, resulting in facial numbness, pain and facial paralysis.
  

Diagnosis and Treatment

Diagnosing acoustic neuroma is a daunting task as the symptoms explained above are associated with many other medical conditions and it could easily be mistaken for middle ear disorder. Once suspected, doctor will advise MRI, the only test conducted to prove the presence of acoustic neuroma. Few of the hearing (audiometry) and balancing (nystagmus) tests are also conducted to assess the hearing and balance functions.

There are three options available to treat acoustic neuroma. The choice of treatment depends upon the size of the tumor, it's location and patient's age and fitness.

Micro surgery involves removing the tumor either partially or totally through surgery. Partial removal is considered when the tumor is large and the total removal leads to the damage of the facial nerve. In case of partial removal, the patient has to undergo repeated MRI scans at regular intervals to ensure that tumor is not growing again. When the tumor does not pose a risk to the adjacent nerves, one can opt for a total removal of the tumor. Though surgery is the most preferred choice of addressing the acoustic neuroma, utmost care should be taken to preserve the hearing function and the facial nerve of the patient.

Radiation is the second best option for treating acoustic neuroma. Radiation is a non-invasive treatment that uses precisely focused, narrow beams of radiation to shrink the acoustic neuroma. Currently, radiation is either delivered as single fraction stereotactic radio surgery (SRS) or as multi-session fractionated stereotactic radiotherapy (FSR). These techniques deliver high doses of radiation to the tumor and also ensure that surrounding areas and organs like brain, skull and skin receive minimum or no radiation.

SRS involves a single dose of radiation wherein multitude of radiation beams are delivered to the tumor in one single sitting. Patient need not return for treatment except for a follow up. Though SRS is very effective, it may not preserve the hearing function in most cases.

In FSR, smaller doses of radiation are given every day, over a period of three to four weeks. FSR method has better chances of preserving the hearing function compared to SRS method.

Sometimes doctors may just ask the patient to wait and watch than begin a treatment for acoustic neuroma. Holding back the treatment is most ideal when the tumor is not producing any symptoms and is small in size (less than 2 cm). Acoustic Neuroma does not require any medical intervention if the tumor is not growing rapidly. The growth of the tumor is normally observed by going for repeated MRI on a regular basis for few years. Wait and watch approach also best suits older patients with small tumors that have stopped growing. They will only be monitored periodically with the help of diagnostic tests.

ABR test

ABR test or Auditory Brainstem Response test is a diagnostic tool that is used to determine a child's ability to hear. The way a child's auditory nerve responds to sounds is measured. The ABR test is used to check a child for a possible hearing problem. This test is also used on patients who are in coma or who have suffered a stroke or acoustic neuroma. Small electrodes are places on the child's head and in front of the ears. These electrodes measure the child's response to sounds that are made through earphones. The audiologist uses this test on newborns who have failed the routine hearing screening test on birth.