RESUMO
The authors report a surgically treated patient with very unusual combination of a giant posterior fossa cyst in cerebellopontine area, Chiari I malformation and syringomyelia in cervico-thoracic area. Ventricles were not dilated. He complained weakness and clumsiness on the right upper extremity. His symptom was attributable to the syringomyelia of cervical spinal cord. The authors managed this patient by removing the arachnoid cyst and cystoperitoneal shunt on the assumption that this cyst has an influence on the formation of Chiari malformation and syringomyelia. After operation there was marked improvement in the motor power in the arm, and a follow-up MRI one month later showed a disappearance of syringomyelia. The authors believe that this very unusual condition is of interest in making the pathogenesis of syringomyelia clear.