Suboccipital decompression for Chiari malformation–associated scoliosis: risk factors and time course of deformity progression

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Object

Chiari malformation Type I (CM-I) is often associated with scoliosis. It remains unclear which subgroups of patients are most likely to experience progression of spinal deformity after cervicomedullary decompression. The authors' goal was to determine the time frame of curvature progression and assess which patient subgroups are at greatest risk for progression of spinal deformity after surgery.

Methods

The authors retrospectively reviewed the records of all pediatric patients with significant scoliosis in whom suboccipital decompression was performed to treat for CM-I during a 10-year period at a single academic institution. Clinical, radiological, and operative variables were assessed as independent factors for failure (worsening of scoliosis) by using a univariate regression analysis.

Results

Twenty-one children (mean age 9 ± 3 years; 4 male) underwent hindbrain decompression for CM-I–associated scoliosis and were followed for a mean of 39 months. All patients harbored a syrinx. Eight patients (38%) experienced improvement in scoliosis curvature, whereas 10 (48%) suffered a progression. Thoracolumbar junction scoliosis (p = 0.04) and failure of the syrinx to improve (p = 0.05) were associated with 5- and 4-fold respective increases in the likelihood of deformity progression. Each increasing degree of preoperative Cobb angle was associated with an 11% increase in the likelihood of scoliotic curve progression (p < 0.05).

Conclusions

Over one third of patients with CM-I–associated scoliosis will improve after cervicomedullary decompression alone. Cervicomedullary decompression is a good first-line option, particularly in children with concordant posterior fossa symptoms. Patients presenting with more severe scoliosis (increasing Cobb angle) or scoliosis that crosses the thoracolumbar junction may benefit from earlier orthopedic involvement and should be monitored regularly for curvature progression after cervicomedullary decompression. In cases in which there is a failure of the syrinx to show improvement after suboccipital decompression, the patients are also more likely to develop curvature progression.

Abbreviations used in this paper: CI = confidence interval; CM-I = Chiari malformation Type 1; HR = Hazard ratio.

Article Information

Address correspondence to: Matthew J. McGirt, M.D., 3553 Newland Road, Baltimore, Maryland 21218. email: mmcgirt1@jhmi.edu.

© AANS, except where prohibited by US copyright law.

Headings

Figures

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    Kaplan–Meier plots of time of onset of curve improvement (upper) and time of onset of curve worsening (lower), indicated by Cobb angle on standing radiographs, as a function of time after hindbrain decompression in children with CM-I. Eight patients (38%) experienced improvement in their scoliosis curvature, and 10 (48%) experienced scoliosis progression postoperatively. Of those patients with improvement, 50% exhibited improvement by 6 months, 88% by 2 years, and all patients by 3 years. Of those patients in whom the deformity worsened, 60% exhibited worsening at 1 year, 80% by 2 years, and all patients by 4 years.

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    Kaplan–Meier plots showing the incidence of curve progression onset as a function of time after hindbrain decompression for CM-I in children. Lack of syrinx improvement (p = 0.05) (upper) and presence of scoliosis at the thoracolumbar junction (p = 0.04) (lower) were associated with an increased risk of scoliosis curvature progression. T-L Jxn = thoracolumbar junction.

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