Final answer:
Blood in the cerebrospinal fluid is considered a contraindication for myelography.
Step-by-step explanation:
A contraindication for myelography is the presence of blood in the cerebrospinal fluid (CSF). Myelography involves the injection of a contrast dye into the spinal canal, which helps to visualize the spinal cord and nerve roots. If blood is already present in the CSF, it can make it difficult to interpret the images and may result in inaccurate findings. Therefore, it is important to identify and address any underlying condition causing the blood in the CSF before considering myelography.