Scoliosis and Chiari 1 malformations: the influence of surgical decompression on scoliosis curve progression

Abstract

John T. Smith, MD, Douglas Brockmeyer, MD, Salt Lake City, UT, USAPurpose: The surgical management of Chiari 1 malformations is controversial. There is a subset of patients with Chiari 1 malformations that develop scoliosis. Within this group, some may develop a syrinx as well. The exact relationship between Chiari 1 malformation, scoliosis and the presence of a syrinx remains unclear. Previous studies have documented a highly variable response between suboccipital decompression and improvement in scoliosis. The purpose of this study is to review our experience with suboccipital decompression for the management of Chiari 1 malformation and analyze the response of the syrinx and the scoliotic curve to surgical decompression.Methods: This is a retrospective review of 85 patients, age 16 years or younger, who underwent surgical decompression for Chiari 1 malformation between 1990 and November 2000. Of these patients, 22 presented with the initial physical finding of scoliosis. Twenty of the 22 patients had an associated syrinx of variable size. One patient had a scoliosis fusion before recognition of their Chiari 1 malformation and syrinx. Fifteen of the 22 curves were convex to the left, and 7 of 22 were convex to the right. All patients were initially managed with suboccipital decompression, C1 laminectomy, lysis of the arachnoid space and duraplasty followed by layered closure of the wound. The mean follow-up for the series was 3.8 years (range, 3 months to 10 years). Patients were followed with plain radiographs to monitor the scoliosis and serial magnetic resonance imaging to evaluate the effect of the decompression on the syrinx.Results:Table 1Table 1*Initial curve (degrees)PatientsImproved worseImprovedWorseFused0–201120–30881230–4033140–507743>502211Total2112274*One patient had fusion before recognition of the Chiari malformation and syrinx. summarizes the response of 21 patients with Chiari 1 malformation and scoliosis to the initial suboccipital decompression. The magnitude of the initial scoliosis was variable; 55% had curves greater than 30 degrees. Fifty-seven percent of curves improved after initial decompression, but 33% worsened. Four of the 21 patients have required fusion for curve progression, with an additional three patients anticipating surgery because of worsening of their curve. Curve progression was greatest for curves greater than 40 degrees at the time of initial presentation. All syrinxes improved with decompression, although the degree of response was variable and difficult to quantify. However, the degree of syrinx improvement did not correlate with curve improvement. There were four complications in the series. One syrinx required shunting after decompression, hydrothorax (1), syringopleural shunt revision (1) and pseudomeningocele repair (1).Conclusion: In this series, 57% of patients presenting with scoliosis, Chiari 1 malformation and syrinx, demonstrated improvement in their curve after suboccipital decompression. Improvement in the scoliosis curve was variable and did not have a consistent relationship with either age at initial presentation or curve severity. After initial improvement, some curves will begin to worsen over time, necessitating careful follow-up until the completion of growth. Curves that are greater than 40 degrees at the time of initial presentation are more likely to progress despite decompression. The response of the syrinx to initial decompression did not predict which curves would be progressive. Early detection and treatment of Chiari 1–related scoliosis remains beneficial, because long-standing significant curves are unlikely to improve after decompression.