One-Year Outcomes of Chiari Type 1 Malformation and Syringomyelia Treated With Posterior Fossa Decompression.

Abstract

This was a retrospective cohort study. The objective of this study was to evaluate posterior fossa structural differences between Chiari type 1 malformation with and without syringomyelia, and assess data of the improvement of syringomyelia after different surgical options. Syringomyelia is among the most common concomitant complications of Chiari malformation (CM). However, posterior fossa decompression cannot definitely make the syringomyelia disappear even in the long term. Also, there are no universal criteria defining improvement in syrinx. All admitted CM patients at our institution from 2013 to 2018 with a 1-year follow-up were analyzed. Patients without syringomyelia were compared with those who had syringomyelia. Patients were divided into 3 groups according to the procedures performed: posterior fossa decompression versus posterior fossa decompression with duralplasty (PFDD) versus PFDD plus obex unblocking. Divergent prognosis of syringomyelia was defined as a 3-category ordinal variable. A multivariable ordinal regression model was used to estimate the relationship between patient variables and increased odds for better resolution of syringomyelia. No significant linear difference in bony structure was found between syringomyelia and nonsyringomyelia patients. Among syringomyelia patients, the regression analysis demonstrated that patients with shorter posterior fossa height ( P =0.032), lower Pavlov ratio ( P =0.029), and obex unblocking (vs. PFDD, P <0.001; vs. posterior fossa decompression, P =0.037) were more likely to gain a better resolution of syringomyelia. Syringomyelia of CM patients may not simply originate from single linear anatomic variation. Patients with shorter posterior fossa height and lower Pavlov ratio received better syringomyelia resolution. Also, unblocking the obex received better syringomyelia resolution compared with duraplasty alone and bony decompression alone with the avoidance of increased postoperative complications and worse clinical outcomes.