Resolution of Primary or Recalcitrant Chiari-Associated Syringomyelia Requires Adequate Cerebrospinal Fluid Egress from the Fourth Ventricle.

Syringomyelia is often resistant to various treatment modalities. Chiari I malformations are associated with syringomyelia in approximately 69% of operative cases. Failure to resolve syringomyelia after Chiari decompression is common. The pathophysiology of Chiari-associated syringomyelia has been well studied, with Oldfield emphasizing the water-hammer mechanism, with treatment limited to bony decompression and duraplasty. On the other hand, capacious fourth ventricular drainage is thought to be essential for syrinx resolution. Persistence or progression of the syrinx after decompression is an indication for reoperation. Direct shunting of the syrinx is associated with high failure rates. The technique of shunting the fourth ventricle has been applied successfully in the pediatric population. We emphasize the need to ensure outflow from the fourth ventricle in Chiari decompressions associated with syringomyelia. In revisions to treat progressive syringomyelia after failed decompression, we undertake the following steps: 1) adequate lateral bony decompression, 2) lysis of scar/adhesions around the cisterna magna, 3) opening the fourth ventricle outlet by releasing any web/adhesions, 4) insertion of a shunt from the fourth ventricle to the cervical subarachnoid space, and 5) bipolar coagulation of the lateral tonsillar pia to maintain patency of cerebrospinal fluid pathways. We favor autologous fascia or pericranium for expansile duraplasty, as the use of nonautologous materials may cause excessive scarring. In this video, we demonstrate these tenets in 3 cases of Chiari-associated syringomyelia, 2 revisions and 1 primary case, with excellent resolution of the syrinx (Video 1). The patients consented to surgery and publication of images.