The MRI provides more information than the CT scan when analyzing the back of the brain and spinal cord, and is usually the preferred test. It can provide an accurate view of the brain, cerebellum and the spinal cord, is very good at defining the extent of malformations, and distinguishing progression. Magnetic resonance imaging (MRI): A diagnostic test that produces three-dimensional images of body structures using magnetic fields and computer technology. There are several tests that can help diagnose and determine the extent of Chiari malformation and syringomyelia, listed most common to least commonly ordered. The central canal, a very thin cavity in the middle of the spinal cord, is a remnant of normal development. Hydromyelia is usually defined as an abnormal widening of the central canal of the spinal cord. As more people are surviving spinal cord injuries, increased cases of post-traumatic syringomyelia are being diagnosed. In these cases, the syrinx forms in the section of the spinal cord damaged by these conditions. This condition can also occur as a complication of trauma, meningitis, tumor, arachnoiditis or a tethered spinal cord. It is thought to be related to the interference of normal CSF pulsations caused by the cerebellar tissue obstructing flow at the foramen magnum. Chiari malformation is the leading cause of syringomyelia, although the direct link is not well understood.
Syringomyelia can arise from several causes. Loss of sensation in an area served by several nerve roots is one typical symptom, as is the development of scoliosis. A wide variety of symptoms can occur, depending upon the size and location of the syrinx. As the fluid cavity expands, it can displace or injure the nerve fibers inside the spinal cord. These are chronic disorders involving the spinal cord, and may be expanding or extending over time. When CSF forms a cavity or cyst within the spinal cord, it is known as syringomyelia or hydromyelia. All of these structures are located just above the foramen magnum, the largest opening at the base of the skull through which the spinal cord enters and connects to the brainstem. The fourth ventricle is a space filled with cerebrospinal fluid (CSF) located in front of the cerebellum (and behind the brainstem). Along the under surface of the hemispheres, there are two small protrusions called the tonsils. Usually, the cerebellum is composed of two lateral halves, or hemispheres, and a narrow central portion between these hemispheres, known as the vermis. The cerebellum controls the coordination of motion and is normally located inside the base of the skull, in what is referred to as the posterior fossa. These malformations, along with syringomyelia and hydromyelia, two closely associated conditions, are described below. The term "Arnold-Chiari" was latter applied to the Chiari type II malformation. He categorized these in order of severity types I, II, III and IV. In the 1890s, a German pathologist, Professor Hans Chiari, first described abnormalities of the brain at the junction of the skull with the spine. Chiari malformation is considered a congenital condition, although acquired forms of the condition have been diagnosed.
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