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Trigeminal Neuralgia

2012; Lippincott Williams & Wilkins; Volume: 71; Issue: 4 Linguagem: Inglês

10.1227/neu.0b013e318266214b

1524-4040

Luis Germán González Bonet, José Piquer,

Facial Nerve Paralysis Treatment and Research

To the Editor: We all know presenting symptoms in Chiari I malformation: pain, weakness, numbness, loss of temperature sensation, painless burns, unsteadiness, diplopia… Recently, articles have been published that relate Chiari type I with trigeminal neuralgia. Perhaps the best review is contained in this journal and was written by Papanastassiou et al1 several years ago. In that article, the authors described a 63-year-old man with a Chiari I malformation and symptoms of trigeminal neuralgia. They also showed beautiful figures of the patient (magnetic resonance imaging) and of the discussion with wonderful illustrations from 1934. However, although they tried to fully explain both processes, it is unclear what may be the real pathophysiology. Papanastassiou et al proposed 4 possible mechanisms: (1) vascular compression at the nerve root entry zone, which could be affected by hydrocephalus or anatomic factors related to the Chiari malformation, such as a small posterior fossa; (2) demyelination; (3) microischemic changes; and (4) direct brainstem compression. Our group thinks that the relationship between Chiari type I and trigeminal neuralgia might be greater than previously thought. This relationship may often be hidden because the retrosigmoid craniectomy with opening of the cisterna magna during a microvascular decompression of trigeminal nerve could treat or relieve a Chiari I malformation, which compresses the structures around the foramen magnum. In our institution, we have collected 4 patients per year with a prevalence rate of patients with trigeminal neuralgia of approximately 5% to 10%. Only 1 patient had syringomyelia, but all of them improved with a suboccipital craniectomy. Thus, we recommend magnetic resonance imaging for trigeminal neuralgia with special attention to the foramen magnum. We also think that the explanation of the pathophysiology is really much simpler. For this purpose, we just have to remember the anatomy of the trigeminal nerve and trigeminal nucleus. On entering the brainstem, all sensory fibers from cranial nerves V, VII, IX, and X terminate in the trigeminal nucleus, which is divided into 3 parts: the mesencephalic trigeminal nucleus (proprioceptor and mechanoreceptor fibers from the jaws and teeth), the main trigeminal nucleus (touch/position fibers), and the spinal trigeminal nucleus (pain/temperature fibers). These pain/temperature fibers are poorly myelinated or unmyelinated. They descend, forming the spinal tract of the trigeminal nucleus, which parallels the spinal trigeminal nucleus until the C2 level (Figure). These fibers are very vulnerable because of their low myelin and dorsal localization, and they are responsible for pain and temperature information.FIGURE: Illustration by González-Bonet in which a Chiari type I malformation can be seen deforming and compressing the descending fibers of the trigeminal nerve (spinal tract of the trigeminal nucleus) and the spinal trigeminal nucleus, both of them responsible for pain and temperature information.Therefore, we conclude that Chiari type I malformation causes trigeminal neuralgia by compression of these fibers around the foramen magnum. In the past 2 years, several articles have been published on bilateral trigeminal neuralgia in the setting of Chiari I malformation, which seem to corroborate our hypothesis.2,3 Disclosure The authors have no personal financial or institutional interest in any of the drugs, materials, or devices described in this article.