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Cranial Nerve Surgery

Different Approaches to Difficult Problems

Cranial Nerve Surgery

What do trigeminal neuralgia, hemifacial spasm, vertigo, glossopharyngeal neuralgia, hypertension, and diabetes have in common? All of these processes have been thought to be related to vascular cross-compression in the lower portion of the brain where the cranial nerves emerge. Vascular cross-compression in this area of the brainstem is a concept which originated with Dandy and Gardner in the early days of neurological surgery and was applied by Jannetta successfully in 1967 when the first microvascular decompression was completed. Jannetta was the first to introduce the microscope for extensive use in this area.

Trigeminal Neuralgia
Vascular cross compression causes the Trigeminal nerve to malfunction creating abnormal areas of sensitivity and secondary pain called trigger zones and paroxysmal pain. This leads to changes within the nerve itself including demyelination and automatic firing. People have termed the latter the ignition hypothesis referring to the ability of a nerve to begin to function autonomously. For patients with complex facial pain syndrome, the differential diagnoses include trigeminal neuralgia, cluster headache, sphenopalatine neuralgia, geniculate neuralgia, occipital neuralgia, anesthesia dolorosa, and atypical facial pain. Trigeminal neuralgia represents the most common neuropathic face pain. Trigeminal neuralgia is characterized by paroxysmal, brief, electric-like pain in one of the three distributions. Microvascular decompression places a piece of felt between the vessel creating the cross-compression and the nerve itself. This is the only non-injurious treatment for trigeminal neuropathic pain. This operation is predicated on the fact that nerve can repair itself once the offending agent is removed. We have over 4000 cases of microvascular decompression for various cranial nerve cross-compression syndromes. For trigeminal neuralgia, the success rate is approximately 88% to 92% and the recurrence rate is 0.5% per year. I also perform glycerol injections, balloon compression, radiofrequency lesioning, and radiosurgery. There are procedures that also help control the pain of trigeminal neuralgia and other forms of facial pain. These include glycerol application, radiofrequency, and balloon compression. These are procedures done a same day basis.

Other forms of Facial pain
Patients are often told they have symptoms of “less than classic” or atypical facial pain. We have found some differences, but many similarities for this group of patients. While some of the traditional medications have not been as successful, other types and forms of application have been helpful for patients so affected. In addition, we recently completed a trial of Microvascular decompression for these individuals, with moderate success.

Dysequilibrium and Vertigo
Malfunction in the hearing and balance nerve can take several forms including tinnitus and ringing, when the hearing portion of the nerve is involved or it can involve vertigo, dizziness, and nausea, as isolated syndromes. If the vestibular portion is involved, we can offer medical treatment or surgery if medication fails. Micro vascular decompression and selective operations in this area have enjoyed an 87% to 91% success rate in reducing the symptoms of dysequilibrium, nausea, and vomiting. Tinnitus is more difficult to treat with a success rate of around 65%. New therapy for tinnitus can include transcranial magnetic stimulation, which has been shown to be efficacious in early trials.

HEMIFACIAL SPASM
In hemifacial spasm, the cross compression reduces the feedback loop between the nucleus and the face allowing for continuous activity, while the reverse is true: vascular cross compression can cause a reduction in the nerve’s ability to work resulting in facial palsy. Hemifacial spasm does not enjoy a respite with any medical therapy, and only the use of botulinum toxin has been effective in reducing the spasm. Unfortunately, this procedure must be repeated once every 12 weeks in most cases and some patients develop antibodies to the agent and become nonresponders over time. Microvascular decompression will alleviate the symptoms in 98% of the cases. Intraoperative technical factors such as the use of monitoring of the hearing and VII nerve have dramatically reduced the complication rate while improving this success rate. Malfunction in the hearing and balance nerve (VIII) can take several forms including tinnitus (ringing) when the cochlear portion of the VIII nerve is involved, and it can involve vertigo, dizziness, and nausea and vomiting as isolated syndromes when the vestibular portions are involved.

HIGH BLOOD PRESSURE
In 1975, Jannetta postulated that vascular cross compression in in the lower portion of the brain (on the left) would produce dysfunction in the sympathetic and parasympathetic nerves related to blood pressure control and that this might be one source of high blood pressure. Research demonstrated we could cause hypertension in a scientific model, then relieve it, then redemonstrate it. This lead to the decompression procedure to control hypertension. Subsequently, clinical procedures involving decompression of this region and elevation of the blood vessel away from the brain stem have been reported for over 1200 patients worldwide. Long term results, especially from the group in China, have documented good blood pressure control three to four years after the procedure. Our experience has been that decompression of this region will result in 50% reduction of the medications in over 70% of patients, and the ability to stop all medications in 15% to 20% of patients.

TYPE 2 DIABETES
The case is similar for Type 2 diabetes. The observation that compression on the lower brain (on the right) side would cause an increase in the activity of the nerve that goes to the organ involved in glucose control, the pancreas, led to an operation to relieve the pressure. The preliminary results are encouraging. Patients with type 2 diabetes are finding lower glucose levels, with less medicines in a number of the cases.