Myelography is a contrast iodinated radiographic study used to highlight the spinal cord within the vertebral canal. While survey vertebral column radiographs do not allow visualization of the spinal cord or the meninges, Myelography with the use of radiographs as described above, allows visualization of the outline of the spinal cord.
The procedure is technical and performed by veterinarians experienced with the procedure. The procedure is carried out under anesthesia. A spinal needle is introduced into the spinal canal as for a spinal tap. For myelography of the entire spine usually lumbar puncture at L4-5 or L5-6 is performed (low back area). After sterile surgical preparation of the skin, the needle is inserted into the subarachnoid space. This space lies between the outer meninges (fibrous covering of the spinal cord) and the spinal cord itself. This space is filled with spinal fluid. The contrast agent is slowly and gently instilled with care until the entire spinal cord can be visualized into the high neck region.
Myelography for many years was the only way to further image the spinal cord. Although it does not allow for imaging the spinal cord itself, because the contrast agent surrounds and thus highlights the spinal cord, it can provide information on diseases causing compression from the outside the cord but within the canal (extra-dural), within the meninges (intra-dural, extramedullary) and also within the spinal cord (intramedullary).
Examples of extradural diseases include: intervertebral disc extrusion, tumors, cysts, infection, hemorrhage, compression from malformation, fracture or instability and other. Examples of intradural-extramedullary diseases include tumors or infection of the meninges/nerve roots, and cysts or dilations or adhesions of the meningeal elements. Intramedullary diseases include tumors of the spinal cord itself, ischemic stroke, hemorrhage, infection, inflammation, cavities (syrinx), traumatic high velocity intervertebral disc rupture and others.