The Chiari malformations: A review with emphasis on anatomical traits

Abstract

Hindbrain herniations come in many forms and have been further subdivided as their original descriptions. For cerebellar tonsillar ectopia, they can be divided into two categories, acquired and congenital. Acquired hindbrain herniations are due to increased intracranial pressure caused by certain conditions such as trauma or brain tumor. Although the mechanism for their formation is not clear, congenital hindbrain herniation makes up the majority of these congenital malformations. Furthermore, these malformations are often found to harbor additional anatomical derailments in addition to the hindbrain herniation whether it be the cerebellar tonsils (Chiari I malformation) or the cerebellar vermis (Chiari II malformation). This article reviews these forms of cerebellar ectopia and describes the details of their anomalous anatomy. Moreover, this article compares and contrasts the differing embryological theories found in this literature.

Sagittal MRI often overestimates the degree of cerebellar tonsillar ectopia: a potential for misdiagnosis of the Chiari I malformation

“…The current diagnosis of Chiari I malformation (CIM) depends mainly on the presence of herniated cerebellar tonsils on MR images and almost exclusively on midline sagittal slices. What constitutes cerebellar tonsillar herniation versus cerebellar tonsillar ectopia is a question that has had varied answers by different authors [2][3][4][5]. With the advent of MRI, it became necessary to formulate criteria that standardize the identification of CIM using MR imaging [2].…”

Tonsillar contusion associated with benign tonsillar ectopia following minor head trauma

“…Increased intracranial pressure subsequent to brain tumor or trauma underlies acquired herniations [1]. Congenital malformations constitute the majority of hindbrain herniations, although the mechanism for their development is ill-defined.…”

Dermoid of the posterior fossa in Chiari II malformation: The first reported case

“…[6] Chiari II malformations were initially thought of as being the caudal displacement of the cerebellar vermis, brainstem, and fourth ventricle. However, it is now known that they represent a complex malformation involving both supratentorial and infratentorial components, in addition to the skull and vertebral elements.…”

“…However, it is now known that they represent a complex malformation involving both supratentorial and infratentorial components, in addition to the skull and vertebral elements. [6]…”