Persistent Syringomyelia After Posterior Fossa Decompression for Chiari Malformation

BACKGROUND: Chiari malformation (CM) is often comorbid with syringomyelia. The treatment of CM via posterior fossa decompression (PFD) may not improve syringomyelia in up to 40% of patients, based on historical cohorts. Management of these patients is problematic, as both reoperation and syrinx shunting have high failure rates in the long term. METHODS: We retrospectively reviewed our cases in which patients with CM type 1 or 1.5 and syringomyelia underwent PFD without postoperative improvement in syringomyelia. Symptomatology and radiographic measurements were collected at presentation and on the first and latest available postoperative scans and analyzed. We present 2 cases to illustrate the challenges in the management of these patients. RESULTS: Our cohort consisted of 48 consecutive patients with CM and syringomyelia who underwent PFD. Of these, 41 patients had postoperative improvement in or resolution of syringomyelia. We subsequently studied the cohort of 7 patients who underwent PFD with (n = 5) or without (n = 2) durotomy and demonstrated worsening of syringomyelia following surgery. This cohort had mean (+SEM) preoperative syrinx area of 23.9 +/- 10.0 mm(2). Postoperatively, the mean syrinx area increased to 40.5 +/- 9.6 mm(2) and 57.3 +/- 12.5 mm(2) on the first and latest postoperative scans available (P = 0.02), for an increase of 106.9% -1 94.4% and 186.0% +/- 107.4% (P = 0.04). Presenting symptoms included occipital headache, paresthesias, visual deterioration, and paraspinal pain. On last follow-up (mean 13.9 +/- 4.9 months), the majority of symptoms were resolved in this cohort, despite persistence of syringomyelia. CONCLUSIONS: In this small cohort of unique patients, syrinx resolution was not achieved via decompression surgery. Despite "radiographic failure," good symptom control was achieved, with most patients remaining or becoming asymptomatic postoperatively, thus supporting our rationale for what has largely been a conservative approach in this population.