What is an Acoustic Schwannomas?

March 08 00:21 2019 Print This Article

It is defined as a condition in which there is a primary intra cranial tumor of the myelin forming cells. It is benign in the nature and involves the vestibule cochlear nerve. It is the 8th cranial nerve. It is also known as the vestibular schwannoma. The term acoustic is a misnomer as the tumor hardly arises from the acoustic division of the vestibule cochlear nerve.

The neuroma is also a misnomer as it means a nerve tumor but this condition is a schwannoma. This condition arises from the Schwann cells as they form the myelin sheath in the peripheral nervous system. In the US alone 3000 cases are diagnosed yearly and show a prevalence of 1 in 1 lacks in the world. Nearly, one tenth of the intra cranial neoplasms are constituted by this disorder in the adults. Their incidence peaks in the 5 and 6th decade and affects both the males and females.

What are the signs and symptoms of Acoustic schwannomas?

It occurs as a loss of hearing or deafness which is ispilateral in nature. The balance is disturbed and there is an alteration in the gait. There occurs nausea and vomiting which is associated with the vertigo. There is a pressure in the ear which is mainly due to the disturbance in normal vestibule cochlear nerve function. Nearly, four out of five patients report tinnitus which is a unilateral high pitched sound which resembles a steam kettle. There are large tumors which can compress the brain stem and may involve the local cranial nerves. The nearby facial nerve can be involved and this may lead to the ispilateral facial weakness.

It is the 7th cranial nerve. It also affects the senses, glandular secretions and taste sensations as it involves the anterior two third of the tongue. The trigeminal nerve is also involved in which there occurs a loss of sensation in the affected side of face and mouth. It is the 5th cranial nerve. There are glosso pharyngeal and vagus nerves which are not commonly involved and they may lead to altered gagging and swallowing reflexes. The large tumors increase the intra cranial pressure and lead to the headache, vomiting, and change in the conscious levels.

What is the treatment of Acoustic schwannomas?

It can be treated with the multiple methods.

1. Mainly it includes the use of surgery along with the radiotherapy. Nearly, one fourth of the conditions are treated with the help of medical management which include the periodic monitoring of the neurological status of the patient. It should be combined with the serial imaging studies and the use of hearing aids.

2. There is a conservative treatment in which the neuromata grow slowly and physician can go for it. There is an observation period in which the tumor is monitored with the help of MRI annually. It helps to know about the growth. The old age patients have this type of disorder. Nearly, half of the acoustic neuromata are not easy to detect over 3 to 5 years. In very few cases the acoustic neuromata shrink spontaneously. The people with this condition die due to the reasons.

3. The growth rate of acoustic neuromata is very slow. It can be observed once in a year. They may lead to the hearing loss and tinnitus.

4. Surgery is the other mode of treatment. It is done by various methods. Each method has few advantages and disadvantages. The tumor is mainly removed by the micro surgery. The radiation treatment does not remove the tumor. It has the potential to stop or slow the growth. The only treatment that deals with the balance symptoms associated with the tumor growth is the surgery. The vestibular nerves are removed at the surgery. The damage to the face or hearing nerves cannot be repaired by the surgery. There are chances of the recurrence of acoustic neuromata after surgery. There is a requirement for the MRI scanning.

5. The choice of the surgical approach depends on the patient age, medical condition and the size of tumor. The pre operative hearing thresh hold and speech discrimination along with the other tests helps to response testing. The patient and surgeon choice also play a crucial role in it. The tumor is removed along with the vestibular nerves. They can be superior or inferior. They cause the loss of vestibular input to the brain. The hearing functions can be improved with the help of other ear. The surgery may cause injury to the facial nerve and requires monitoring. The small acoustic neuromata give better results.

6. There are mainly three surgical approaches which are used. The first one is the trans labyrinthine approach which completely eliminates the hearing in the affected ear. It is mainly used in the patients who have not well speech differentiation. This technique can remove the tumor of any size. No brain retraction occurs by this procedure and is considered to be the safest technique to remove the tumor. The patients which have the type 2 of acoustic neuromata undergo brain stem transplantation. It provides the direct path to the lateral recess and cochlear nucleus.

7. The other two approaches include the sub occipital retro sigmoid and middle fossa are mainly the hear preservation approaches. They can preserve some or full hearing of the patients. The neuro surgeons prefer this type of approach as they are more familiar to it. The middle fossa approach is used in case of tumors which are less than 2 cm in size. This technique is better than the retro sigmoid as it gives a direct access to the lateral end of internal auditory canal. The retro technique cannot reach the lateral part of internal auditory canal and has been proven in many studies. It cannot violate the posterior semi circular canal and can destroy the hearing.

8. The other approach which can be used is the minimal invasive endoscopic surgery. It is available in the specialized centers. The acoustic neuromata surgery is technique demanding and is preferred by the neuro surgeons alone or in combination with the oto laryngologist.

9. There is a radiation therapy which is done in multiple ways. It includes the gamma knife radio surgery which is also known as the fractionated stereotactic radiotherapy. It occurs with a linear accelerator and proton therapy. In the gamma knife radio surgery technique around 200 beams of gamma radiations are focused in a single session on the tumor. The tumor may be damaged at the convergence point which may stop the growth. It does not cause the shrinkage in the long term. The short term shrinkage may occur due to the necrosis of tumor. The damage may occur to the tumor cells and its vasculature. The high dose radiations were used previously but the failure rate was just 12 percent. After the radiation therapy these tumors are difficult to remove. The radiation does not remove the tumor and when the irradiated tumors are removed surgically they have growing tumor cells in them.

10. There are certain risks which are associated with the radiation therapy. It includes the carcinogenic progression of acoustic neuroma from benign to malignant. There is also induction of the other tumors like glio blastoma in the nearby surrounding tissue of brain. This is the irradiated part. The incidence of these events is very low and occurs in 1 to 1000 cases. The incidence is higher in the patients of the type 2 of acoustic neuromata. This calculation is based upon the dividing of number of cases of tumor progression and a report of secondary tumor by the gamma knife procedures. It is done with the help of medical literature. This method is not valid scientifically and is questionable. It estimates the carcinogenic risk of medical radiation exposures. There is a possibility of the re growth of tumor or presence of secondary tumor. So, the radiation treatment for this disorder must be followed by the MRI for rest of the patient life. The MRI is a costly procedure. The long term effect of the gamma knife surgery has not been established properly.

11. The fractionated stereo tactic therapy uses a beam of ionizing radiations which focus on the tumor from a moving base. They have a wider beam which is not accurate than the gamma knife technique. Its total dose is also higher and this technique helps in the sparing of normal tissue. This technique has been not widely used as gamma knife procedure. The follow up study for many years is not there to confirm it. The control of tumor by this method has not been proven. The incidence of the secondary effects is not known.

12.The linac machine shows a lot of variations and can confuse the individual. There is a modified collimator which is referred as the Peacock and there is a miniature linac machine which is attached to the robot arm and is guided by the x ray imaging. It is referred to cyber knife. It checks the position of patient between the treatment shots.

13. There is a proton therapy machine which uses the beam of protons to kill the tumors. The beam is generated by the cyclotron. It is more preferred than the x rays which are used by the linac and gamma knife machines. They can be stopped before they exit the tumor and prevent the damage to normal tissue. A few people have been treated by this method and the results are not too encouraging.

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