Pathology of chiari I and II malformations

Abstract

Chiari I and Chiari II malformations are generally categorized as primary cerebellar anomalies, although critical review of their morphological features indicates that the cerebellar component more often is a secondary abnormality rather than a primary developmental defect. The basic malformation involves that portion of basicranium that comprises the posterior fossa; essentially it is too small. With a few exceptions, the non-bony abnormalities associated with Chiari I are secondary. In contrast the constellation of lesions that form Chiari II are complex and affect all levels of the neuraxis to a greater or lesser degree and consist of a combination of primary malformation and acquired lesions. Ironically, the cerebellar abnormalities more often fall into the acquired category.