Relationship of cine phase-contrast magnetic resonance imaging with outcome after decompression for Chiari I malformations.

OBJECTIVE: Many patients with symptomatic Chiari I malformations experience symptom recurrence after surgical decompression. Identification of predictors of outcome is needed to better select patients most likely to benefit from surgical intervention. We examined whether or not cerebrospinal fluid (CSF) flow dynamics assessed by cine phase contrast magnetic resonance imaging could independently predict response to posterior fossa decompression for Chiari I malformations.

METHODS: Pre- and postoperative CSF flow dynamics were assessed by cine phase-contrast magnetic resonance imaging in 130 consecutive patients receiving posterior fossa decompression for a Chiari I malformation between 1997 and 2003. CSF flow was classified as "abnormal" if biphasic flow was either absent or decreased through the aqueduct, fourth ventricle and its outlets, the foramen magnum, or ventral or dorsal to the cervical spinal cord. If no evidence of decreased flow was noted, CSF flow was classified as "normal." The association between preoperative CSF flow dynamics, all recorded variables, and long-term outcome was assessed using multivariate proportional hazards regression analysis.

RESULTS: All patients had tonsil herniation more than 5 mm below the foramen magnum (average, 11 +/- 5 mm). Abnormal hindbrain CSF flow was observed in 81% of patients (43% complete obstruction, 38% reduced flow). Normal CSF flow was observed in 19% of patients. In multivariate analysis, patients with normal preoperative hindbrain CSF flow were 4.8-fold more likely to experience symptom recurrence after surgery (relative risk, 4.85; 95% confidence interval, 1.88-12.5; P < 0.001) regardless of degree of tonsillar ectopia or presence of syringomyelia. Isolated frontal headache (relative risk, 4.16; 95% confidence interval, 1.7-9.8; P < 0.05) and scoliosis (relative risk, 9.2; 95% confidence interval, 1.7-10.5; P < 0.001) also were independent risk factors for symptom recurrence.

CONCLUSION: Normal preoperative hindbrain CSF flow was an independent risk factor for treatment failure after decompression for Chiari I malformation regardless of the degree of tonsillar ectopia. Cine phase-contrast magnetic resonance imaging may be a valuable tool in identifying patients who are less likely to respond to surgical decompression for Chiari I malformation.