Acoustic Neuroma

                                                                                                                                                                                         Photo by Mark Thomas Acosta
About Acoustic Neuromas

The diagnosis of an acoustic neuroma, also known as a Vestibular Schwannoma,usually is suggested by the presence of hearing loss, ringing in the ear, and sometimes dizziness. Sometimes they cause subtle symptoms, such as only sound distortion, ear fullness, facial pain, or slight unsteadiness. Because of the possibilities of undiagnosed acoustic tumors, people with symptoms consistent with acoustic tumors should be thoroughly evaluated by a neurotologist, or someone familiar with these tumors, their characteristics, and treatment options.

Acoustic Neuromas Defined

Acoustic Neuroma (Vestibular Schwannoma) are fibrous growths which originate from one of the balance or hearing nerves. They are not malignant. They do not spread to other parts of the body, other than by direct extension. They occur at a rate of approximately one per 100,000 individuals per year in the general population. They constitute approximately 10% of all brain tumors. They are located between the brain and the inner ear, adjacent to vital brain centers. As they grow, they can involve the adjacent facial, hearing, and balance nerves, and they can progress to involve other cranial nerves with further growth. If they grow quickly and/or are allowed to grow over a long period of time, they may compress vital brain centers, eventually cause pressure on the brainstem, and ultimately can be fatal. In most cases, these tumors grow slowly (approximately 1-2 mm per year); however, in some people the growth is quite rapid and can cause the size to actually double in a single year. At times, multiple symptoms may develop.

Many diagnostic procedures are available to make an accurate diagnosis and to determine the functional deficits caused by the tumor. In treating these tumors, the preservation of life is the most important objective. The second objective is to preserve as many cranial nerves and other vital structures as possible. In most cases, a completely normal life results following surgery. Rarely does one have a severe degree of handicap.

Diagnosis of Acoustic Tumors

In our office, the diagnosis of an acoustic neuroma (tumor) begins with a complete history, physical examination, and conventional audiologic evaluation. Following this, if there are any indications of a tumor, screening with an Auditory Brainstem Response (ABR) test is typically performed. Indications for further testing include asymmetry in hearing, sudden or rapidly progressive hearing losses, tinnitus, and dizziness. The ABR test uses a sophisticated computerized audiometer to analyze the electrical activity of the hearing nerves on both sides to determine if there is normal conduction of nerve signals from the inner ear to the brain. If the conduction is slowed down on one side, this may indicate a tumor. Vestibular testing (VNG and VEMP) can also be used to test for acoustic neuromas and determine which vestibular nerve is involved. If the balance mechanism is damaged on one side, this may be indicative of a tumor on that side. Magnetic resonance imaging (MRI) and CT scanning are sophisticated imaging methods used to examine (by picture) the internal auditory canal and cerebellopontine angle region of the brain to determine if there is a tumor present.

Treatment

If an acoustic tumor is identified, three main treatment options exist: observation,radiation, and surgery. Since these tumors frequently grow slowly, sometimes the recommendation for observation is made, particularly when patients are older and/or have other health problems making surgery a riskier undertaking.

Steriotactic radiosurgery or Gamma Knife and Cyber Knife treatment of acoustic tumors are also options for helping to halt growth and possibly shrink the size of the tumor (particularly small tumors). As with conventional surgery, risks still exist to the surrounding nerves and brain structures with the radiation treatment. It will not completely remove or kill all the tumor cells. It may slow the growth of the tumor by decreasing the blood supply. The use radiationdoes complicate future “salvage” surgery should the tumor continue to grow and necessitate surgery.

The other treatment option for acoustic neuromas is surgery, which may allow complete tumor removal (i.e. cure). The main goal is the preservation of life, with a minimum of future physical disturbances. To accomplish this, a team consisting of a neurotologist (ear and skull base sub-specialist), neurosurgeon, anesthesiologist, specially trained surgical nurses, and sometimes internists are involved in the surgery and the pre and postoperative care. The neurotologist and the neurosurgeon are co-surgeons during the surgery. The patient is usually admitted to the intensive care unit for 24-48 hours postoperatively for close observation. Patients usually are in the hospital for a total of 4-7 days.

There are special surgical techniques to remove the tumor and preserve hearing. The techniques or approach is depended upon the age or health of the patient, tumor size, status of hearing in the opposite ear, and the status of hearing in the ear involved with the tumors. hearing preservation can be attempted using approaches referred to as themiddle fossa approach and sub-occipital approach. Each approach has both advantage and disadvantages. A third approach is the translabyrinthine technique. This approach requires passing through the inner ear structures and provides excellent ability to remove the tumor completely while exposing and preserving the facial nerve. Hearing cannot be preserved with this technique. Occasionally a combination of approaches are utilized with some acoustic tumors.

Other Brainstem Tumors

Other brainstem tumors can present with similar symptoms and in a similar location as acoustic neuromas. The most common alternate tumor is called Meningiomas. These tumors are benign and are treated in a similar fashion as acoustic neuromas as described above.

For more information on Acoustic Neuroma treatment, click the following link: Treatment of Acoustic Tumors