Introduction: Syringomyelia is a known sequela of Chiari I malformations in children. Syringomyelia can lead to myelopathy and scoliosis. Surgery is generally recommended for Chiari I malformations found in conjunction with syringomyelia. Theories about the mechanism of syrinx formation in Chiari I malformation abound. This study was designed to identify associative factors between the two.

Methods: After obtaining IRB approval, a retrospective review of all patients undergoing Chiari I decompression at Children’s Hospital of Pittsburgh from January 2005 through Sept 2010 was performed. 41 patients were identified to have syringomyelia (syrinx group). These patients were compared to 40 patients without syringomyelia (non-syrinx group). Data points collected included age, Chiari size (in mm of cerebellar tonsillar decent below the foramen magnum), and presence of an arachnoid web at the foramen of Magendie.

Results: For the non-syrinx group the mean age at operation was 11.7 years old; for the syrinx group, the mean age was 9.8 years old. (p=0.039). The incidence of arachoid web at the time of surgery was 5% in the non-syrinx group, and 41.5% in the syrinx group. (p=.0001) The mean Chiari size in the non-syrinx group was 13.2 mm, and in the syrinx group it was 14.5mm in the syrinx group (p=0.406).

Conclusions: The incidence of arachnoid web formation in conjunction with syrinx formation in Chiari I malformations is underestimated. Arachnoid web formation may be the cause of syringomyelia in a significant number of patients with Chiari I malformation. Identification and fenestration of an arachnoid web should be a standard part of Chiari I decompressive surgery, particularly in the setting of a syrinx.

Patient Care: To recommend instituting a practice of exploration for arachnoid webs, during a posterior fossa decompression to improve resolution of syringomyelia in the setting of Chiari I malformation

Learning Objectives: 1.)Arachnoid web formation may be the cause of syringomyelia in a significant number of patients with Chiari I malformation. 2.)Identification and fenestration of an arachnoid web should be a standard part of Chiari I decompressive surgery, particularly in the setting of a syrinx.

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