Expansion of Chiari I-associated syringomyelia after posterior-fossa decompression

Chiari I malformation (CMI) is an abnormality that involves caudal herniati on of the cerebellar tonsils into the foramen magnum. CMI has been shown to be closely associated with the development of syringomyelia (SM). Objects: Several theories have emerged to explain the apparent correlation between the existence of CMI with subsequent development of SM. However, the exact mechanism of the evolution of SM is still subject to controversy. We report here the case of a 12-year-old girl admitted to hospital with headache, vo miting, ataxia, and moderate pyramidal signs. Methods: Radiological evaluat ion revealed the presence of CMI, accompanied by a small SM. The patient un derwent posterior fossa decompression and improved significantly. She was r e-admitted 6 months later with clinical evidence of progressive spinal cord dysfunction. MR revealed gross expansion of the syrinx. Conclusions: This case raises questions regarding the pathophysiology of CMI and its associat ion with SM. The case indicates the need for neurological and radiological followup for patients undergoing posterior fossa decompression due to CMI, even for those without an initial syrinx. This is the first report known to us of expansion of a syrinx following decompression of an associated CMI.