Anatomic Features Common to the Arnold-Chiari and the Dandy-Walker Malformations Suggest a Common Origin
. . . . in every . . . . art, fundamental matters are perennially being discovered, discredited, forgotten, rediscovered and reaffirmed . . . .John Homans1
MILD examples of the Arnold-Chiari and Dandy-Walker malformations were described in adults by Chiari,2,3 by Walker,4 as well as by subsequent authors. Gardner, Abdullah, and McCormack5 have shown that the mild examples of these two malformations found in adults have so many anatomic features in common that they must arise from a common cause, namely, embryonal atresia of the fourth ventricle. The purpose of this communication is to point out that the same is true of the severe forms encountered in the hydrocephalic infant.
Definition of Terms
Chiari,2 in 1891, described in detail three degrees of a deformity of the hindbrain that he attributed to hydrocephalus of the forebrain. This description appeared three years prior to Arnold's6 incidental and quite incomplete account of the same deformity. Chiari's type 1 deformity, now usually referred to as a “pressure cone,” consisted essentially of a herniation of the cerebellar tonsils through the foramen magnum. His type 2, subsequently entitled the “Amold-Chiari malformation” by Arnold's students,7 consisted of a herniation of the inferior vermis, pons, medulla, and the compressed fourth ventricle through the foramen magnum with a steplike formation of the medulla and a shortening of the cervical cord. In his type 3, the cerebellum was herniated into a high cervical meningocele. In his commonly quoted second paper, Chiari3 reported 14 cases of type 1, all . . .