Tonsillar herniation spectrum: more than just Chiari I. Update and controversies on classification and management

Neurosurg Rev. 2020 Dec;43(6):1473-1492. doi: 10.1007/s10143-019-01198-x. Epub 2019 Nov 10.


Cerebellar tonsil herniation comprises a spectrum of disorders sharing a common neuroimaging finding consisting of downward displacement of the cerebellar tonsils through the foramen magnum and into the upper cervical spinal canal. This not uncommon condition may result from a large host of congenital or acquired causes, and confusion regarding its classification and pathogenesis still exists. Terminology also remains heterogeneous, including inconsistencies in the usage of the "Chiari 1" monicker. In this paper, the hypothesized mechanisms of development of tonsillar herniation are reviewed and strategies of management are discussed, with particular attention to surgical options adapted to the underlying etiology. A focus will be placed on acquired causes of tonsillar herniation.

Keywords: Cerebellum; Chiari; Foramen magnum; Herniation; Pediatric; Tonsil.

Publication types

  • Review

MeSH terms

  • Arnold-Chiari Malformation / classification*
  • Arnold-Chiari Malformation / diagnostic imaging
  • Arnold-Chiari Malformation / surgery*
  • Cerebellar Diseases / classification*
  • Cerebellar Diseases / diagnostic imaging
  • Cerebellar Diseases / surgery*
  • Hernia / classification*
  • Hernia / diagnostic imaging
  • Hernia / therapy*
  • Humans
  • Magnetic Resonance Imaging
  • Neurosurgical Procedures / methods