In patients where there is concern of cerebrospinal fluid (CSF) flow abnormalities, invasive tests, such as myelograms or cisternograms may be necessary.
Such abnormalities include trapped fluid in pockets (arachnoid cysts) or leakage of fluid out of the central nervous system (CNS). These procedures are performed by injecting a dye or tracer directly into the CSF space, usually by a lumbar puncture.
When symptoms are thought to be related to the spine, a myelogram is prescribed. This images the CSF fluid along the entire spinal cord and nerve roots into the sacrum (pelvis). Conditions where this may be helpful include intracranial hypotension (low brain pressure) due to spontaneous CSF leakage, spinal arachnoid cysts or Chiari malformations.
When symptoms are likely cranial in origin, a cisternogram is prescribed. In addition to imaging the spinal cord, this shows CSF fluid flow in the brain as well. Indications for this test may include nasal CSF leakage (CSF rhinorrhea) or intracranial arachnoid cysts.
Dyes and Tracers
CT myelograms/cisternograms require injection of contrast dye and is helpful to show high-resolution anatomy of the fluid with relation to the bony and nervous structures.
Nuclear myelograms/cisternograms require injection of a radioactive tracer and is helpful to demonstrate subtle leaks. It is more sensitive than CT myelography. In addition, gauze (pledgets) can be placed at potential sites of leakage (e.g. in the nose) and the radiation can be measured to identify occult (hidden) leaks.
There is a small risk of allergic reaction to the dyes and tracers used.