History, anatomic forms, and pathogenesis of Chiari I malformations.

INTRODUCTION: Chiari I malformations constitute a group of entities of congenital or acquired etiology that have in common descent of the cerebellar tonsils into the cervical spinal canal. In recent years, since the advent of magnetic resonance imaging, an increasing number of asymptomatic, doubtfully symptomatic, and minimally symptomatic patients with Chiari I malformations have been diagnosed. This has resulted in controversy about the multiple therapeutic strategies indicated for these problems. OBJECT: With the intention of updating the knowledge that we currently have on the Chiari I malformation and the related syringomyelia we review the literature and discuss the historical background, pathogenesis, anatomic forms, clinical presentation, and diagnostic procedures of these abnormalities.