Despite the extensive literature on the pathology of hydrocephalus, little attention has been given to the sequential changes in the region of the cerebellum produced by cerebral hydrocephalus.... I will indicate several types of these changes in the following selected cases, and will reserve a full description for a later report.
The first type consists of elongation of the tonsils and the medial portions of the lobi inferiores... of the cerebellum into conical extensions that accompany the medulla oblongata and extend into the vertebral canal....
It is my impression that this elongation results from hydrocephalus of the cerebrum, specifically the chronic hydrocephalus established early in life (congenital hydrocephalus). I never have found it in the absence of hydrocephalus, and never with acute hydrocephalus or hydrocephalus of late onset. But I have found it in a large percentage of cases of chronic congenital hydrocephalus. Apparently we are dealing with a developmental
Chiari H. Concerning Changes in the Cerebellum Due to Hydrocephalus of the Cerebrum. Arch Neurol. 1971;25(4):377–379. doi:10.1001/archneur.1971.00490040103014