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Cranial nerve Schwannomas
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Cranial nerve Schwannomas are benign, slow-growing tumors of the distal cranial nerves and account for 2% of all primary brain tumors. They occur most commonly in the fifth and sixth decades of life. Sensory nerves tend to be affected, with the most common site being the superior vestibular portion of the eighth cranial nerve. This tumor is most commonly referred to as the acoustic neuroma. Other cranial nerve origins are much less common. Acoustic neuromas present with a unilateral high-frequency sensorineural hearing loss.Speech discrimination is often a problem and patients will often complain of difficulty understanding telephone conversations with the affected ear. Dizziness and tinnitus (ringing in the ear) are also prominent symptoms. Tumors occasionally grow large enough to produce adjacent cranial nerve dysfunction, symptomatic cerebellar compression, and hydrocephalus.
Traditionally, micorsurgical removal has been the "gold standard" of treatment. Complete surgical resection is usually possible and newer techniques of intraoperative monitoring can minimize the inherent risk of adjacent cranial nerve dysfunction. However, the safety, efficacy and cost-effectiveness of Gamma Knife radiosurgery has, we feel, made it the treatment of choice for acoustic neuromas less than 3 cm in diameter. The risk of facial nerve injury (resulting in facial weakness or paralysis) is extremely low today with improved imaging, "tighter" treatment planning with smaller collimators or "shots", and lower doses. By the same token, preservation of hearing is more likely with radiosurgical rather than microsurgical treatment of these tumors. Other problems that go hand-in-hand with an open, microsurgical removal (i.e., incisional pain, headache, time off work, spinal fluid leakage, infection and other potential medical complications) are completely avoided with radiosurgery. Tumors larger than 3 cm. can still be treated with radiosurgery, but the disadvantages begin to outweigh the advantages in this group of patients. Obviously, the age and overall medical condition of the patient weigh into this decision. In addition, the degree of brainstem compression and neurologic condition of the patient are important considerations. In some cases of large and/or cystic tumors, a staged intracapsular (internal) debulking of the lesion can be followed by radiosurgery to the remaining tumor in the hopes of avoiding many of the above-noted problems. |
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