Arnold-Chiari Malformation

Abstract

The clinical findings and results of surgery in 33 cases of Chiari type I and II malformations were reviewed. Twenty patients with Chiari malformations were examined by magnetic resonance imaging (MRI), which furnished valuable information concerning the pathogenesis of and surgery for these malformations. MRI provided precise delineation of 1) the extent of herniation of the cerebellar tonsils and inferior vermis; 2) the degree of compression of the upper cervical cord and medulla; 3) the extent of cervicomedullary kinking; 4) the condition of the spinal cord, particularly whether or not a syringohydromyelia was present; 5) the nature of the communication between the fourth ventricle and syringohydromyelia or subarachnoid space; 6) the association of craniocervical anomalies and other brain malformations; and 7) the overall ventricular size. MRI also revealed the position, extent, and inner architecture of the syringohydromyelia, which could be classified as one of two types: smooth and cylindrical without septa, or a fusiform, expanded cavity having transverse septae or narrow, tubular interconnecting segments. For the latter type, syringostomy appeared not to be indicated. On the basis of the surgical results and the findings obtained by MRI, surgical bony and dural decompression in the region of the foramen magnum and upper cervical canal appear to be sufficient therapy in cases of Chiari malformations without syringohydromyelia. For those accompanied by syringohydromyelia, separation and wide opening of the fourth ventricle in addition to bony and dural decompression may be desirable. This procedure establishes a free flow of cerebrospinal fluid from the fourth ventricle and basal cistern to the spinal subarachnoid space.