Time course of syringomyelia resolution following decompression of Chiari malformation Type I.

OBJECT: To better understand syrinx pathophysiology, the authors performed a prospective study in which they used findings from serial clinical and magnetic resonance (MR) imaging examinations performed before and after craniocervical decompression to establish the time course of syrinx narrowing.
METHODS: Serial clinical examinations and cervical MR imaging were performed in 29 consecutive patients with Chiari malformation Type I (CM-I) and syringomyelia before surgery, 1 week, and 3-6 months after surgery, and then annually. Time to narrowing of the syrinx (>50% decrease in maximal anteroposterior diameter) following surgery was calculated using the Kaplan-Meier method.
RESULTS: All syringes decreased in diameter and length (number of segments) on MR images at 3-6 months, 1 year, and 2 years or later. The syrinx diameter decreased from 6.9+/-2.1 mm (mean+/-standard deviation) preoperatively to <1.5 mm at last evaluation (p<0.0001). The median time to syrinx narrowing was 3.6 months following CM-I decompression (95% confidence interval 3.0-6.5 months). After surgery 94% of patients had improved symptoms, but symptoms resolved incompletely in 68% of patients; 52 and 59% of patients had residual dysesthesias and sensory loss, respectively. Clinical improvement occurred before partial or complete disappearance of the syrinx on MR images. Patient age, duration of symptoms, sex, preoperative syrinx diameter, and length of syrinx were unrelated to time to syrinx narrowing.
CONCLUSIONS: Most patients improve after decompression for CM-I, but many have residual symptoms. Syringes may continue to diminish for months to years after surgical decompression. A collapsed syrinx (absence of distention of the spinal cord) indicates that the pathophysiology has been reversed by treatment regardless of the completeness of elimination of the cavity on MR images.