Intraoperative ultrasonography used to determine the extent of surgery necessary during posterior fossa decompression in children with Chiari malformation type I.

OBJECT: In this retrospective analysis, the authors report a prospective study in which intraoperative ultrasonography was used to determine the extent of surgery necessary during posterior fossa decompression surgery for Chiari malformation Type I (CM-I) in children.
METHODS: Between 1995 and 2003, posterior fossa decompression was performed in 149 patients (mean 5.9 years of age, range 9 months-18 years of age) with CM-I. Of these, 130 underwent intraoperative ultrasonographic evaluation of the craniocervical junction (CCJ) and 15 did not. Four patients with craniosynostosis were excluded from the study. Duraplasty and tonsillar shrinkage were performed when ultrasonographic evidence showed significant decreases in cerebrospinal fluid (CSF) or abnormal tonsillar piston action. Surgical success was determined on the basis of clinical outcome and need for reoperation. One hundred and twenty-four (95.5%) of the children had successful outcomes following surgery and six (4.5%) experienced continued or worsening symptoms requiring reoperation. Forty patients did not undergo duraplasty because the ultrasonography evidence showed adequate decompression with bone removal alone. Of 90 patients with significant compression, decreased CSF dynamics, and/or abnormal tonsillar piston-like action at the CCJ, 85 underwent duraplasty and tonsillar shrinkage and five did not for various reasons. One patient in whom the dura mater was violated accidentally during bone decompression subsequently underwent duraplasty. Hospital stays lasted 6.4 +/- 3.9 days (mean +/- standard deviation) when duraplasty was performed compared with 4.3 +/- 1.1 days when it was not (p < 0.0003). After bone decompression alone, no patient experienced complications. After duraplasty, 12 patients experienced complications and had headaches, nausea, and pain more often than patients who underwent bone decompression alone. Mean tonsillar descent was 11 +/- 4 mm after bone decompression only and 13.9 +/- 4.9 mm after duraplasty, with tonsillar shrinkage (p < 0.0003) seen on magnetic resonance imaging.
CONCLUSIONS: In patients who undergo decompressive surgery for CM-I, intraoperative ultrasonography may be a useful tool to aid the surgeon in deciding whether to opt for bone removal only or bone removal plus duraplasty and tonsillar shrinkage.