Differentiation between symptomatic Chiari I malformation and asymptomatic tonsilar ectopia by using cerebrospinal fluid flow imaging: initial estimate of imaging accuracy.

PURPOSE: To determine the sensitivity and specificity of cerebrospinal fluid (CSF) flow imaging in distinguishing between patients with symptomatic Chiari I malformation and those with asymptomatic tonsilar ectopia by using a neurosurgeon's overall clinical determination as the reference standard.

MATERIALS AND METHODS: The institutional review board of the University of Wisconsin Hospital and Clinics approved our HIPAA-compliant retrospective study and granted a waiver for informed consent. Seventeen patients (five male, 12 female; aged 4-43 years) with tonsils extending more than 5 mm below the foramen magnum were classified by the neurosurgeon as symptomatic for Chiari I malformation or asymptomatic for tonsilar ectopia. The CSF flow images of the two groups were read independently in blinded fashion by four neuroradiologists. Reader agreement was calculated as percentage of readings in each patient that agreed with the neurosurgeon's classification. Sensitivity and specificity were respectively calculated as the percentage of abnormal readings in symptomatic patients and the percentage of normal readings in asymptomatic patients.

RESULTS: Of 17 patients, nine were classified by the neurosurgeon as symptomatic Chiari I malformation and eight as asymptomatic tonsilar ectopia. Agreement between pairs of readers was 63%-44%. For sagittal and transverse images, reader sensitivity for finding abnormal flow in symptomatic Chiari I malformation patients averaged 76% and specificity for normal flow in patients with asymptomatic tonsilar ectopia averaged 62%. The number of positive readings in the symptomatic patient group was significantly greater than that in the asymptomatic group (P < .02).

CONCLUSION: Readers detected an abnormal CSF flow pattern significantly more often in patients with symptomatic Chiari I malformation than in patients with asymptomatic tonsilar ectopia.