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[Chiari malformation (type I) associated with bilateral abducens nerve palsy: case report].

There are still many questions concerning the pathology and therapeutic strategy for Chiari malformation. We recently encountered a case of Chiari malformation associated with only bilateral abducens nerve palsy which was successfully treated by foramen magnum decompression. The pathology and mechanisms of Chiari malformation (type I) were evaluated in this case. The patient was a 12-year-old girl who had visited our institute 1 month previously complaining of diplopia. She had no particular past or family history and her general appearance was also normal. Bilateral abducens nerve palsy was the only neurological deficit. Her cerebrospinal pressure was 9 cm H2O. Neuroradiological findings revealed basilar impression, C4-6 syringomyelia and Chiari malformation (type I), but no hydrocephalus or meningocele. Foramen magnum decompression with lateral extension, upper cervical laminectomy and open duraplasty were performed. The position of both eyes recovered fully shortly after surgery, and diplopia occurred only when the patient looked sideways. Eye movements also returned completely to normal 3 months after surgery. MRI showed no syringomyelia 4 months after surgery, the upward shift of the pendulous portion of the cerebellar tonsil, and the expansion of the subarachnoidal space of the pons-oblongata junction. In conclusion, it was thought that the mechanism of bilateral abducens nerve palsy in this case was due to the strangulation and the downward traction of the pons-oblongata junction. The nerve was relieved from this traction by foramen magnum decompression.