Associated Disorders of Chiari Type I Malformations

A Review

Marios Loukas, M.D., Ph.D.; Brian J. Shayota, B.S.; Kim Oelhafen, B.S.; Joseph H. Mill er, M.D.; Joshua J. Chern, M.D., Ph.D.; R. Shane Tubbs, M.S., P.A.-C., Ph.D.; W. Jerry Oakes, M.D.


Neurosurg Focus. 2011;31(3):e3 

In This Article

Abstract and Introduction


A single pathophysiological mechanism of Chiari Type I malformations (CM-I) has been a topic of debate. To help better understand CM-I, the authors review disorders known to be associated with CM-I. The primary methodology found among most of them is deformation of the posterior cranial fossa, usually with subsequent decrease in volume. Other mechanisms exist as well, which can be categorized as either congenital or acquired. In understanding the relationship of such disorders with CM-I, we may gain further insight into the process by which cerebellar tonsillar herniation occurs. Some of these pathologies appear to be true associations, but many appear to be spurious.


In the late 19th century, Hans Chiari[7] discovered and classified 3 types of rhombencephalic congenital anomalies that would later be termed Chiari malformation Types I, II, and III. Dr. Chiari postulated that the cerebellar herniation might have been due to hydrocephalus with the 3 different types representing various degrees of disease progression.[31] In the ensuing years, Chiari's mechanism of pathogenesis would be disproven as the primary cause of CM-I. Among the classifications, however, no current consensus exists for the exact pathogenesis or treatment regimen for all.[67] Many have formed theories such as the hindbrain dysgenesis and developmental arrest theory, caudal traction theory, small posterior fossa/hindbrain overgrowth theory, hydrocephalus and hydrodynamic theory of Gardner, and the lack of embryological ventricular distention theory, yet no single theory has been able to prove a single pathway in the pathogenesis of CM-I.[3,12,15,30,34,36,40,42,43,47,55,70,75] This article, however, will not review each of those theories. Instead, it intends to document the conditions associated with CM-I to potentially provide insight into how the pathophysiological mechanism of one condition, no matter how remote, might lead to the development of CM-I. Many of these associations are summarized in Table 1. It should also be noted that many of these associations may be incidental; an asymptomatic hindbrain hernia has been identified due to testing for other pathological entities (such as endocrinopathies).