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ACOUSTIC NEUROMA (VESTIBULAR SCHWANNOMA) & FACIAL NERVE TUMORS INTRODUCTION "ACOUSTIC NEUROMA" (VESTIBULAR SCHWANNOMA) and FACIAL NERVE Tumors are an area of specific interest for the Neurosurgeons and staff of Neurosurgical Consultants. Their successful treatment in most cases involves the use, where applicable, of highly advanced Minimally Invasive Microsurgical Techniques. This revolutionary concept in Neurosurgery greatly limits the amount of surgical exposure required and therefore, limits the amount of tissue that is touched and retracted during the operation. Some procedures incorporate Endoscopic Techniques, which are conducted through very small holes in the skull. This results in less post-operative pain, earlier mobilization, diminished hospital stay, less risk for complications, an earlier return to activities as well as lower overall costs.Among our team's particular focus is the PRESERVATION OF HEARING in patients with these tumors. ACOUSTIC NEUROMA (VESTIBULAR SCHWANNOMA) is a benign (non-malignant) tumor that arises from Schwann cells that surround the Vestibular Nerve (which is a part of the Eighth Cranial Nerve complex). Schwann cells serve a particular function to form Myelin, the insulating portion of nerves that are outside the Brain and Spinal Cord. Therefore, the term Vestibular Schwannoma may be preferred as being the more accurate term. Most of these tumors are not "Neuromas" and most arise from the superior (upper) division of the Vestibular Nerve, not from the Cochlear (also known as the Acoustic) Nerve. FACIAL NERVE NEUROMA is a rare benign tumor of the Seventh (7th) Cranial Nerve, which shares the Internal Auditory Canal with the Eighth (8th) Cranial Nerve complex. The Neurosurgeons of Neurosurgical Consultants have an exceptional experience with successful, complete resection of this tumor with preservation of hearing and Facial Nerve function. Facial Nerve Neuromas are unusual, almost always completely benign tumors of Schwann Cells that account for a very small number of the Brain and Cranial Nerve Tumors while comprising only 0.8% of all "mass lesions" that involve a critical part of the Skull Base called the "Petrous Ridge". Facial Nerve Neuromas can arise from any segment of the 7th Cranial Nerve from the Cerebellopontine Angle to the "extra-temporal" peripheral portion which can create a variety of clinical situations depending on their location, size and relationship to the Auditory Apparatus. Please see below for a more complete discussion of Facial Nerve Neuromas.) "ACOUSTIC NEUROMAS" (VESTIBULAR SCHWANNOMA) are one of the most common intracranial tumors, comprising 8-10% of tumors. The annual incidence is 0.78-1.15 cases per 100,000 individuals, resulting in approximately 2300 new cases per year in the United States. As with most other intracranial tumors the exact cause of these tumors is unknown. However, the association of Vestibular Schwannoma tumors with Neurofibromatosis Type 2 (NF-2) may lead to some insight into the cause. The incidence of "Acoustic Neuromas" in patients with NF-2 is increased, with many patients having these tumors bilaterally. NF-2 is caused by a genetic abnormality on chromosome 22. Therefore, "Acoustic Neuromas" that arise in other patients may have a similar abnormality. SYMPTOMS Tumor size is closely correlated to the types of symptoms experienced by these patients. One-sided hearing loss, ringing in the ears and problems with equilibrium (dysequilibrium) are related to pressure on the 8th Cranial Nerve. The hearing loss is slowly progressive in most patients, and is often first noticed as difficulty in hearing conversation while on the telephone. The ringing in the ears is high pitched. By the time of diagnosis of an "Acoustic Neuroma" is made, most patients have these two symptoms.Facial numbness, facial weakness, and changes in taste occur as the tumor causes pressure on the 5th and 7th Cranial Nerves. These symptoms do not usually occur until the tumor is a large size. Larger tumors cause pressure on the Brain Stem, which can cause the following symptoms: difficulty with balance, headache, nausea/vomiting, double vision, coma, difficulty breathing, and death. These large tumors can also cause pressure on the lower cranial nerves causing difficulty swallowing and hoarseness of the voice. Symptom frequency varies as follows:
DIAGNOSIS Audiometric and Audiologic Studies are done as baseline studies to determine the function of hearing on both sides, with particular attention to the affected ear. Pure tone audiograms are useful as an initial screening test, since they identify high tone hearing loss. In addition, a speech discrimination test is performed to determine the functional usability of the hearing.Neuroimaging Thin Slice Contrast MRI is the most accurate and useful diagnostic test for this tumor. The MRI reliably identifies 98% of tumors, and has almost no false positive risk. The characteristic finding is a round or oval-shaped "enhancing" (meaning that it takes up the "contrast" material, Gadolinium, that is injected into the patient's vein during the MRI examination) tumor, centered on the Internal Auditory Canal. Large tumors may show cystic appearing areas. CT scan with contrast is the second procedure of choice. The CT scan gives good information about the bony landmarks surrounding the tumor; however, its soft tissue imaging is less well defined compared with MRI scans.TREATMENT OPTIONS Masterful Inactivity and Cat-like Observation (otherwise known as "Do Nothing").Some "Acoustic Neuromas" grow slowly or not at all, and 6% actually decrease in size. This option is typically reserved for patients who: refuse any treatment, have a very small tumor and are without many symptoms, or are elderly with many medical complications, and have a small or medium sized tumor. These patients need to understand that, with time, the tumor will probably cause complete hearing loss in the affected ear. Periodic MRI scans are performed to follow the size of the tumor. "Intracanalicular Acoustic Neuroma" - Treatment Controversy The controversy regarding the treatment of a patient with an "Intracanalicular Acoustic Neuroma" relates to the "projected natural history" (what will happen if no treatment is given) of this tumor. In the absence of sequential MRI Scans over a period of time THERE IS NO WAY TO DETERMINE THE RATE OF GROWTH OF THESE TUMORS, particularly in patients who have NO SYMPTOMS. There is minimal risk to these patients, if they choose to avoid any form of treatment. However, follow-up scans should be done.In the event that such a patient subsequently develops symptoms including Hearing Impairment, it becomes clear that this tumor is growing and that the ability of the Nerve to accommodate to and sustain the pressure being exerted upon it is now compromised. At this point treatment options should be reviewed. IF THE PATIENT WISHES TO PRESERVE USEFUL HEARING, then a RERTOMASTOID CRANIECTOMY APPROACH IS APPROPRIATE. In our opinion, an ASYMPTOMATIC patient with an Intracanalicular Acoustic tumor should NOT feel compelled to undergo ANY FORM of treatment UNLESS THEY WISH TO PRESERVE HEARING in the affected ear. THE RISK TO LIFE and/or MAJOR NEUROLOGICAL DETERIORATION, from an Intracanalicular Acoustic Neuroma, IS MINIMAL. In a patient who WISHES TO PRESERVE HEARING then ONLY a RETROMASTOID APPROACH IS APPROPRIATE (See Figures 7A & 7B below.) Stereotactic Radiosurgery This is rapidly becoming a preferential treatment option for many patients with small or medium sized tumors. Previously (and still in many institutions) this treatment option has been reserved for patients who have residual tumor after surgery, are elderly, or have multiple medical problems making surgery too risky. Radiosurgery is more effective for smaller tumors and certainly should be avoided for tumors over 3 centimeters in size.The goals of radiosurgery are, to hopefully, prevent the tumor from getting any larger. This occurs in 85% of the patients. The tumor may shrink in size, but usually does not disappear. The advantages of this form of Radiation Therapy are that it is non-invasive, easily tolerated and can be effective in controlling tumors of limited size. The disadvantages are primarily related to the swelling of the tumor as it is being subjected to and damaged by the radiation. Any injury to Brain, Spinal Cord or Nerves, results in "swelling". This is a problem for cases of Vestibular Schwannoma/Acoustic Neuroma since all of them have a major portion lying in the narrow bone passage within the Skull Base called the Internal Auditory Canal (IAC). Swelling of the irradiated tumor puts considerable pressure on the Facial, Vestibular and Cochlear Nerves, which live within that Canal. Therefore the real risks to Radiosurgery include:
Surgery This is generally the best treatment option for most patients because it has the best chance of curing the patient. In addition, a surgical option offers the only opportunity to conserve hearing in those patients who still have useful hearing. The Neurosurgeons of Neurosurgical Consultants have a long history of hearing preservation in selected cases of Acoustic Neuroma.Different Surgical Approaches The choice of what approach to use depends on the size and location of the tumor, the symptoms of the patient, and the surgeon's operating preference. It is possible to save the hearing in a selected minority of cases. As a general rule, one should acknowledge that the larger the tumor the lower the chance for hearing preservation. The state of hearing prior to surgical intervention is an important predetermining factor regarding hearing preservation. While not impossible, it is most unlikely to improve hearing by removing the tumor. In some cases with minimal or poor hearing it is better to sacrifice the hearing in order to remove the entire tumor.Suboccipital Retromastoid Approach This approach is used for larger tumors and/or where hearing preservation may be possible. This involves performing a small Craniotomy (opening the skull immediately behind the ear on the affected side), to gain access to the tumor. This is usually the best approach for larger tumors that cause compression of adjacent structures such as the Brain Stem. Reconstructive Cranioplasty (repairing the skull defect with a thin perforated titanium plate), at the time of surgery generally diminishes post-operative headaches that many patients experience in the absence of Cranioplasty.Translabyrinthine Approach With this approach, the hearing and balance mechanism of the inner ear are sacrificed. Therefore, the affected ear is made permanently deaf, and the patient's balance may be impaired for a variable period of time. The benefits of this approach are a diminished risk to injury of and preservation of the Facial Nerve (the 7th Cranial Nerve). The significant negative aspects of this approach are permanent hearing loss in the affected ear, imbalance, higher risk to Brain Stem injury for large tumors and higher rate of Cerebrospinal Fluid (CSF) leak.Middle Cranial Fossa Approach This approach is typically reserved for patients who have a small tumor and who have good hearing in their affected ear since it may permit preservation of hearing and still remove the tumor. This technique has significant limitations in that it may not be able to remove the whole tumor and in half of all patients (who have useful hearing to begin with); the surgeon will not be able to preserve hearing. Additionally there is greater chance of harming the Facial Nerve. While there are surgeons who express a preference for this approach, the Neurosurgeons of Neurosurgical Consultants do not favor it.Incomplete Tumor Removal The goal of the management, in most cases of Acoustic Neuromas, is total removal of the tumor without complications. Nevertheless, there are clinical instances where the surgeon exercises his judgment, in the patient's best interest, to leave tumor behind rather than risk the chance of serious additional neurological injury. The options for the management of patients with residual tumors include repeat operation at a later date, Stereotactic Radiosurgery, or to follow the tumor size with serially conducted MRI scans. On rare occasion, particularly for Giant Tumors, staged sequential operations may be required.Surgical Risks
HEARING CONSERVATION Acoustic Neuroma (Vestibular Schwannoma) Tumors are an area of specific interest for the Neurosurgeons and staff of Neurosurgical Consultants. Among our team's particular focus is the PRESERVATION OF HEARING in "Acoustic Neuroma" patients. Their successful treatment in most cases involves the use, where applicable, of highly advanced Minimally Invasive Microsurgical Techniques. Some procedures incorporate Endoscopic Techniques as well.While preservation of hearing is possible for patients in whom there is reasonably functional hearing pre-operatively, it is an extremely difficult goal to attain from a surgical technical standpoint. There is no way to predict beforehand whether or not this effort will prove successful. Intra-operative Neurophysiological monitoring of hearing is conducted on all of these cases along with the monitoring of other Cranial Nerves. Additional Information is available on the Acoustic Neuroma Association website at Anausa.org. FACIAL NERVE NEUROMA Facial Nerve Neuromas (which can occur at any age and have no significant gender predilection) are relatively rare, with approximately 500 cases having been reported in the medical literature. These tumors are generally regarded to be slow-growing. They arise from the Schwann cell sheath or the Facial (7th Cranial) Nerve.The Facial Nerve takes a fairly long course from its origin in the Brain Stem, through the Internal Auditory canal and then twisting and turning through the Skull Base as it makes its way to exit the skull and enter the muscles of the face. Although any segment of the Facial Nerve may be involved with a neuroma, it is quite common for these tumors to involve more than one segment of the Facial Nerve. The majority of Facial Nerve Neuromas originate from the "intra-temporal" portion of the Facial Nerve. SYMPTOMS Facial weakness and hearing impairment (sensorineural-type) are the usual symptoms that bring a patient with a Facial Nerve Neuroma to their doctor for evaluation. The clinical presentations of Facial Nerve Neuromas depend on the location of the tumor. Facial Nerve Tumors that arise within the Internal Auditory Canal (IAC) usually cause hearing impairment and "dizziness" first. Tumors of the Geniculate Ganglion, Tympanic and Mastoid segments produce Facial Nerve "dysfunction" which ranges from facial muscle spasm to paralysis. Facial Nerve Neuromas that involve the Tympanic portion of the nerve can cause "conductive-type" hearing loss. Facial Nerve tumors that lie outside the skull (extra-temporal) will present as a palpable mass within the Parotid Gland.DIAGNOSIS Modern, high-resolution MRI and CT scanning are imperative in order to obtain an accurate diagnosis, to define the precise dimensions of the tumor, and to choose the most appropriate treatment method.TREATMENT This is one clinical situation that really demands the involvement of the patient in making the important treatment decisions that potentially result in altering their quality of life.Hearing Conservation For tumors confined to the Internal Auditory Canal (IAC) and in whom useful hearing persists, then a HEARING CONSERVATION procedure using a Retromastoid approach is recommended. If hearing has already been lost and the tumor is confined to the IAC, then a Translabyrinthine technique may be appropriate.Facial Nerve Management Nevertheless, most Facial Nerve Neuromas exhibit a more diffuse or extensive involvement of the Facial Nerve including the Geniculate Ganglion and "labyrinthine" portion (see Figure 9 above) of the Facial Nerve, which most usually requires a middle cranial fossa or translabyrinthine approach. Rarely is it possible to "separate" the tumor, in this location, from the Nerve. In order to surgically excise this subtype of tumor, one must remove the involved portion of the Facial Nerve which will result in complete Facial Nerve paralysis. The surgeon will plan to insert a reconstruction nerve graft as part of the definitive operation. The result of removal of the tumor and this portion of the nerve is the complete paralysis of that side of the face until the "new" nerve regenerates which can take 1 year or longer. Once "re-growth of the Nerve" has occurred and facial "animation" has returned, movement is likely to be somewhat disorganized since the "fascicle to fascicle" line-up will be altered. This is called "aberrant regeneration". It is for this reason that early diagnosis may improve the outcome of Facial Nerve function, since the likelihood of a successful graft is partially dependent upon the duration of the pre-operative paralysis.When "Not to Operate" For patients with a Facial Nerve Neuroma who have normal or near normal Facial Nerve function, a reasonable alternative is "careful observation" coupled with serially performed high quality neuroimaging (usually MRI Scan) imaging. This will give a more accurate estimate of the biological behavior in that patient. Once this patient demonstrates significant progression in the extent of neurological impairment and/or intracranial extension, surgical treatment becomes a serious consideration.Stereotactic Radiosurgery Stereotactic Radiosurgery (or "Focused Beam" Radiation) is an alternative treatment consideration for some patients with small or medium sized tumors. This is still a relatively new field with very limited experience with long term follow-up in this unusual sub-group of patients. This treatment option is certainly appropriate for patients who have residual tumor after surgery, are elderly, or have multiple medical problems making surgery too risky. However, it may also be a preferential method to attempt to control tumor growth in patients who have no tolerance for the temporary neurological deficit of Facial Nerve paralysis which is associated with complete removal of the tumor. Radiosurgery is more effective for smaller tumors and certainly should be avoided for tumors over 3 centimeters in size.The goals of Radiosurgery are, to hopefully, prevent the tumor from getting any larger. This occurs in 85% of the patients. The tumor may shrink in size, but usually does not disappear. The advantages of this form of Radiation Therapy are that it is non-invasive, easily tolerated and can be effective in controlling tumors of limited size. The disadvantages are primarily related to the swelling of the tumor as it is being subjected to and damaged by the radiation. Since this type of radiation is targeting a relatively discrete area within the bone of the skull, injury to Brain, Spinal Cord or Nerves, is unlikely unless the tumor is directly adjacent to those structures. This may cause a hearing deficit for cases of Facial Nerve Neuroma involving the portion of the Nerve that lies directly adjacent to the lateral (or outside) portion of the Internal Auditory Canal (IAC). Considerable care must also be exercised if the tumor has extended to involve the Internal Carotid Artery as it negotiates it way through the Skull Base to enter the intracranial region. The real risks to Radiosurgery include:
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All content ©2024 by Neurosurgical Consultants, P.A. Author, Martin L. Lazar, MD, FACS All Rights Reserved. See Usage Notices. |