Figure 135

Angiography showing a large AVM within the upper cervical cord (arrows). Note the vessels connecting the AVM to the vertebral arteries. Courtesy Dr. T. Miller.

Imaging studies. The best diagnostic modality is MRI. It may show flow voids, cord displacement due to the ventral fistula, and cord hyperintensity on T2WI. Postcontrast studies will demonstrate multiple enhancing intradural vessels.

Management. These lesions can be embolized and operated upon.

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Syringomyelia (from syrinx meaning tube and myelos meaning marrow, referring to the spinal cord) is a condition in which a longitudinal cavity forms within the spinal cord. The syrinx, which is separated from the spinal canal, is filled with cerebrospinal fluid (CSF) and usually extends over several spinal segments. As it evolves, it may enlarge the affected cord region and compress the cord from within.

Syringomyelia can occur anywhere along the cord and is frequently found in separate locations within the cord presenting as short longitudinal cavities. When the syrinx is located in the brain stem it is called syringobulbia.

The pathophysiological mechanisms leading to the formation of syringomyelia are still poorly defined and debatable. It is believed that syrinx formation is related to abnormalities of CSF physiology. Impaired outflow of CSF at the fourth ventricle or increased CSF flow into the spinal canal due to increased intracranial venous pressure combined with hindbrain anomalies are two common theories proposed to explain the development of syringomyelia.

Syringomyelia has been classified into five categories: communicating, post-traumatic, tumor-related, arachnoiditis-related, and idiopathic.

In over 50% of syringomyelia patients Chiari malformation may be found. In these patients the syrinx is usually located in the cervical cord, with occasional extension into the thoracic cord. Syringomyelia can develop following spinal cord injury, spinal trauma, or spinal surgeries, and in patients with intramedullary tumors, adhesive arachnoiditis, spinal dysraphism, tethered cord, myelitis, or spondylosis. The pathogenesis of post-traumatic syringomyelia is multifactorial and may include hematoma formation within the cord, liquefaction, necrosis, and meylomalacia. When a syrinx is detected without any other association a complete neuroimaging evaluation of the entire neuraxis should be obtained in order to rule out a remote cord or brain stem pathology. In post-traumatic and postoperative patients the syrinx is most commonly found in the thoracic region and around the site of the original spinal injury and may extend above and below the level of injury. The interval between the original spinal trauma and the appearance of a syrinx varies from several months to many years.

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