Acoustic neuroma is a medical condition characterized by slow growing non malignant tumor on the myelin sheath covering the nerve connecting the ear and brain that are responsible for hearing and balancing (vestibulocochlear nerve, the 8th cranial nerve). As this type of lesion arises from the Schwann cells of the myelin sheath of the 8th cranial nerve, it is also known as vestibular schwannoma. This condition is usually diagnosed in people between 30 and 60 years of age and its prevalence is equal in both the sexes.
Although this condition is not very common still about 3000 new cases are diagnosed per year in the US alone. Acoustic neuroma grows very slowly and most of the presenting symptoms occur due to compression of the adjacent brain structures. Most common presenting symptoms include facial muscle weakness, ringing sound in the year, difficulty in maintaining balance etc.
In case of small and very slow or not growing tumors monitoring at regular time intervals is recommended, however in large symptom producing and fast growing tumors surgical intervention is required.
Symptoms
In most of the patients symptoms of acoustic neuroma occur due to compression of the adjacent structures like blood vessels, nerves or certain brain structures.
Usually symptoms become evident with increase in the size of the tumor; however, sometimes a small tumor may produce symptoms because of its location near an important brain structure(s) and subsequent compression of the structures.
Depending upon the compressed structures different types of symptoms arise; these are
1. Gradual hearing loss which may affect one or both side
2. Ringing sound (tinnitus) in the ear
3. Poor maintenance of balance leading to difficulty in maintaining normal posture and gait
4. Dizziness sometimes there could be blackout
5. Paralysis of facial muscles resulting into slurring of speech and masking of facial expressions, numbness in the facial region
Rarely acoustic neuroma may compress the brainstem and kill the patient
Number of complications may arise due to acoustic neuroma; these are loss of hearing, paralysis of facial muscles leading to difficulty in speaking, swallowing, etc., inability to maintain normal posture and gait, continuous ringing sound in the ear leading to hearing problem, etc. Rarely the tumor can become so large that it can interfere with drainage of the cerebrospinal fluid (CSF) which circulates in the brain and the spinal cord mainly to provide nutrition. Inappropriate drainage of the CSF may cause excessive fluid accumulation in the brain leading to hydrocephalus.
Causes
Myelin sheath is the protecting covering on the neurons. Acoustic neuroma arises from the Schwann cells of the myelin sheath of the 8th cranial nerve (vestibulocochlear nerve). The 8th cranial nerve extends from the brain to the internal ear; there are two parts of the nerve. One part helps in maintaining balance and the other part helps in the transmission of sound.
In most of the cases of acoustic neuroma the tumor arises because of a genetic malfunction on chromosome 22. Under normal circumstances this gene produces proteins which help in growth of the Schwann cells; presence of the malfunction gene may lead to development of tumor from the Schwann cells. It is yet to be known what causes malfunctioning of this chromosome 22.
In neurofibromatosis type 2, a rare neurological disorder this malfunctioning gene is inherited and usually schwannomas may arise on the 8th cranial nerves on both sides.
Risk factors include suffering from neurofibromatosis type 2 and exposure to even low grade radiation in the head and neck area during childhood.
Treatment
Treatment options depend upon the size, location and the severity and nature of the presenting symptoms.
In case of a small slow growing tumor with minimal symptoms regular monitoring at about 6 to 12 months interval through imaging and hearing tests is adequate.
For larger symptom producing and fast growing tumors surgical intervention is required. The options are stereotactic radiosurgery and direct surgical removal of the tumor.