[Arnold-Chiari malformation in adults. Development of diagnostic conditions since the availability of MRI].

We reviewed retrospectively 47 patients with a Chiari malformation (CM) who had been admitted to the Clinique de Neurologie of Lyon from 1971 to 1991. The purpose of this report is to assess the possible influence on the frequency and the clinical pattern at presentation of CM since 1985 when Magnetic Resonance Imaging (MRI) became available to us. A diagnosis of CM was made for 21 patients before 1985 (group 1) and for 26 patients thereafter (group 2), i.e., a 2.5 increase of incidence of CM frequency (1.5 patients/year before 1985 vs 3.7 patients/year thereafter). This increase was even more striking for cases without syringomyelic symptoms and signs (SSS) (42.9% in group 1, vs 76.9% in group 2). The accuracy of clinical diagnosis was 68.1% for the total surveyed period (90.5% before 1985 and 50% thereafter). For cases with SS at presentation, a syringomyelic cavity was radiologically demonstrated in 80% of the cases in the pre-MRI period and 90.9% of the cases since MRI was available. On the other hand, when a syringomyelic cavity was radiologically demonstrated, there was a related clinical SS in 70% of group 1 patients and 50% of group 2 patients.