|
What is Acoustic Neuroma?
|
Important Points To Know About an Acoustic Neuroma:
- An acoustic neuroma is a benign tumor.
- It is usually slow growing and expands at its site of origin.
- The most common first symptom is hearing loss in the tumor ear.
- The cause is unknown.
- A large tumor pushes on the surface of the brain but does not grow into the brain tissue.
- Continued tumor growth can be life threatening.
- The treatment options are observation, surgical removal or radiation.
What is an Acoustic Neuroma?
An acoustic neuroma (sometimes termed a vestibular schwannoma or neurolemmoma) is a benign (non-cancerous) tissue growth that arises on the eighth cranial nerve leading from the brain to the inner ear. This nerve has two distinct parts, one part associated with transmitting sound and the other sending balance information to the brain from the inner ear. These pathways, along with the facial nerve, lie adjacent to each other as they pass through a bony canal called the internal auditory canal. This
canal is approximately 2 cm. (0.8 inches) long and it is here that acoustic neuromas originate from the sheath surrounding the eighth nerve. The facial nerve provides motion of the muscles of facial expression.
Small
Acoustic Neuroma
|
Medium
Acoustic Neuroma |
Large
Acoustic Neuroma
|
Acoustic neuromas usually grow slowly over a period of years. They expand in size at their site of origin and when large can displace normal brain tissue. The brain is not invaded by the tumor, but the tumor pushes the brain as it enlarges. The slowly enlarging tumor protrudes from the internal auditory canal into an area behind the temporal bone called the cerebellopontine angle. The tumor now assumes a pear shape with the small end in the internal auditory canal. Larger tumors can press on another nerve in the area (the trigeminal nerve) which is the nerve of facial sensation. Vital functions to sustain life can be threatened when large tumors cause severe pressure on the brainstem and cerebellum part of the brain. Tumors are typically described as small (less than 1.5 cm.), medium (1.5 cm. to 2.5 cm.) or large (more than 2.5 cm.).
Are Acoustic Neuromas hereditary?
No. Although there is an inheritable condition called neurofibromatosis which can lead to acoustic neuroma formation in some people, most acoustic neuromas occur spontaneously without any evidence of an inheritable pattern.
How often do Acoustic Neuromas occur?
Most recent publications suggest that the incidence of acoustic neuromas is rising.
This is because of advances in MRI scanning both on incidental scans and for
patients experiencing symptoms. Studies in Denmark published in 2004 show the
incidence is 17.4 per million or close to 2 persons per 100,000. Most acoustic
neuromas are diagnosed in patients between the ages of 30 and 60.
Cause or Epidemilogy of Acoustic Neuroma
Most patients inquire, how did this tumor occur? While many theories exist, sudies have hinted at exposure to loud noise on a consistent basis. There are even controversies on hand held cellular phones. Whether or not the radiofrequency radiation has anything to do with their formation, remains to be seen. Other studies mention the prior exposure to head and neck radiation, and a concomitant history of having had a parathroid adenoma (tumor found in proximity to the thyroid gland controling calcium metabolism).
Neurofibromatosis (NF2)
NF2, a genetic disorder, occurs with a frequency of 1 in 30,000 to 1 in 50,000 births. The most perplexing problem are those patients who are slowly losing their hearing due to bilateral tumors. Here a decision about the timing and management of patients with NF2 lesions is notoriously difficult. The trend is to postpone surgery until hearing begins to deteriorate. But studies by Derald E. Brackman, M.D. and colleagues have the opinion to take a proactive approach in bilateral tumors in which hearing is still present. They have reviewed individuals who have undergone middle fossa surgery and found that when tumors are less than 1.5 centimeters in size, surgery may be appropriate. Hearing preservation was obtained in 70% of cases. The situation is much more complex for individuals with NF2 and only one hearing ear-conservatism and observation may be more appropriate here. Stereotactic radiosurgery may not have the same effect on the NF2 patient as in patients with unilateral sporadic tumors. Recent studies have shown that these indiviuals may have more tumors that are resistant to radiation, due to the cell type.
|
|
