The diagnosis of an acoustic tumor (properly called a Vestibular Schwannomas) 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 neuotologist, or someone familiar with these tumors, their characteristics, and treatment options.
Acoustic Tumors Defined
Acoustic tumors (Vestibular Schwannomas) are fibrous growths which originate from the balance and hearing nerve, and 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 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 cause involvement of the adjacent facial and hearing nerves, as they progress to 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 brain, 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 actually double in size in a single year. At times multiple symptoms may develop.
Many diagnostic procedures are used to make an accurate diagnosis and to determine how extensive the tumor is. In treating these tumors, the preservation of life is the most important objective. The second objective is to preserve as many vital structures as possible. In most cases, a completely normal life results following surgery. In others, and mildly uncommon, does one have a severe degree of handicap.
Diagnosis of Acoustic Neuroma
In our office, the diagnosis of an acoustic neuroma begins with a complete history, physical examination, and conventional audiologic evaluation. Following this, if there are any indications of a tumor, an Auditory Brainstem Response (ABR) test is done with a computerized audiometer. 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. Electronystagmography (test of the balance system) is also used to test for acoustic neuromas. 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. Since acoustic neuromas are closely associated with the seventh cranial nerve, which gives movement to the same side of the face, a special test of facial nerve function (Electroneuronography) may also be performed.
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 have other health problems making surgery a riskier undertaking. Steriotactic radio surgery or gamma knife treatment of the acoustic tumors is also an option for helping to shrink the size of the tumor. As with conventional surgery, risks still exist to the surrounding nerves and brain structures with the radiation treatment. Gamma Knife Therapy will not completely remove kill all the tumor cells. It may slow the growth of the tumor by decreasing the blood supply. The use of gamma knife therapy does complicate future "salvage" surgery should the tumor continue to grow.
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, neurosurgeons, anesthesiologist, specially trained surgical nurses, and sometimes internists are involved in 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 hearing in the ear involved with the tumors. These approaches are referred to as the middle fossa approach and sub-occipital approach. Each approach has both advantage and disadvantages.
The best approach and safest is the translabyrinthine technique. This approach is through the inner ear structures and provides the best ability to remove the tumor completely and preserve the facial nerve. Hearing cannot be preserved with this technique. Occasionally a combination of approaches are utilized with some acoustic tumors |
