Hidalgo Joaquin A., Tork Craig A., Varacallo Matthew A.
University of Mississippi Medical Center
Tripler Army Medical Center
Arnold-Chiari malformation, or simply Chiari malformation, is the name given to a group of deformities of the posterior fossa and hindbrain (cerebellum, pons, and medulla oblongata). Issues range from cerebellar tonsillar herniation through the foramen magnum to the absence of the cerebellum with or without other associated intracranial or extracranial defects such as hydrocephalus, syrinx, encephalocele, or spinal dysraphism. Chiari malformations are classified based on their morphology and severity of anatomic defects, typically through imaging (or autopsy). Chiari I is the least severe and is often found incidentally. It is characterized by one or both pointed (not rounded) cerebellar tonsils that project 5 mm below the foramen magnum, measured by a line drawn from the basion to the opisthion (McRae Line). Chiari II malformation is characterized by brainstem herniation and a protruding cerebellum, in addition to the herniated cerebellar tonsils and vermis, resulting from an open distal spinal dysraphism/myelomeningocele. Chiari III involves the herniation of the hindbrain (cerebellum with or without the brainstem) into a low-occipital or high-cervical meningoencephalocele. Chiari IV is now considered obsolete. Before becoming an obsolete diagnosis, it was already a more controversial and rare variant that demonstrated severe cerebellar hypoplasia, similar to primary cerebellar agenesis. Previously, some stated that myelomeningocele could be present while others argued that the presence of myelomeningocele should then be classified as a Chiari II with a vanishing cerebellum. There are other reported, yet controversial, classifications, including Chiari 0, Chiari 1.5, and Chiari V. Chiari 0 is characterized by syringomyelia without hindbrain herniation. At the same time, Chiari 1.5 is considered a progression of Chiari I, characterized by increased cerebellar tonsillar descent and some involvement of the brainstem. Chiari V, the most severe variant, represents cerebellar agenesis with occipital lobe descent and herniation through the foramen magnum.
阿诺德 - 奇亚里畸形，或简称为奇亚里畸形，是指一组后颅窝和后脑（小脑、脑桥和延髓）的畸形。问题范围从小脑扁桃体通过枕骨大孔疝出到小脑缺失，伴有或不伴有其他相关的颅内或颅外缺陷，如脑积水、脊髓空洞症、脑膨出或脊柱裂。奇亚里畸形根据其形态和解剖缺陷的严重程度进行分类，通常通过影像学检查（或尸检）。奇亚里I型是最不严重的，常为偶然发现。其特征是一个或两个尖锐（而非圆形）的小脑扁桃体从枕骨大孔下方突出5毫米，通过从颅底点到枕骨后点（麦克雷线）绘制的线测量。奇亚里II型除了因开放性远端脊柱裂/脊髓脊膜膨出导致的小脑扁桃体和小脑蚓部疝出外，还包括脑干疝出和高耸的小脑。奇亚里III型涉及后脑（小脑伴或不伴有脑干）疝入低位枕部或高位颈部脑膨出。奇亚里IV型现在被认为已过时。在成为过时诊断之前，它就是一个更具争议性且罕见的变体，表现为严重的小脑发育不全，类似于原发性小脑发育不全。以前一些人认为可能存在脊髓脊膜膨出，而另一些人则认为脊髓脊膜膨出的存在应归类为小脑消失的奇亚里II型。还有其他有争议的报道分类，包括奇亚里0型、奇亚里1.5型和奇亚里V型。奇亚里0型的特征是无后脑疝出的脊髓空洞症，而奇亚里1.5型被认为是奇亚里I型的进展，小脑扁桃体下降增加且脑干有一定受累。奇亚里V型是最严重的变体，表现为小脑发育不全伴枕叶下降并通过枕骨大孔疝出。
