Chari 1 malformation, a radiologic finding of caudal cerebellar tonsillar displacement, has a clinical course that can range from benign to complications involving life-threatening hydrocephalus. While the pathophysiologic processes underlying this variation in outcome remain a matter of scientific debate, the clinical realities and decision-making conundrums that these patients pose require a coherent approach to this entity. In this review, we seek to highlight the various processes underlying the development of hydrocephalus in patients with Chiari 1 malformations. Hydrocephalus may occur as a cause, consequence, or in parallel with the development of Chiari 1 malformation, and understanding the etiology of such hydrocephalus is critical to the treatment of Chiari 1 malformations with associated hydrocephalus. We further discuss the literature pertaining to the management of these patients and unify the current scientific thinking on Chiari 1 malformations with the extant data on operative management of Chiari 1 to develop a structured and pragmatic approach to the diagnosis and management of patients with Chiari 1-associated hydrocephalus.
Keywords: Chiari; Chiari decompression; Chiari malformation; foramen magnum; hindbrain; hydrocephalus; posterior fossa.