Musculoskeletal Imaging

Myelography

a radiographic technique for imaging the spinal cord after injection of a contrast agent into the subarachnoid space. This method is, however, more costly and more invasive than CT or MR imaging. Indications for its use include:

  • evaluation of cervical radiculopathy, especially if the results of a cervical CT scan or MR image are ambiguous;

  • confirmation of complete block of the subarachnoid space; and

  • detection of cysts within the spinal cord or subarachnoid space.

    However, MR imaging is preferred for evaluation of spinal cord disorders.

    Myelography demonstrates intervertebral disc displacement indirectly, by means of a characteristic change in the contour of the opacified dural sac or root sheath. In lateral projections, an indentation of the dural sac termed a double density sign is an indication of a herniated disc. However, the most reliable myelographic indication of a herniated disc is shortening and "trumpeting" of a nerve root sheath, in which the nerve root itself appears widened as a result of either oedema or compression and elevation.

    A bulging anulus fibrosus appears on myelography as a curvilinear, thumbprint-like impression on the opacified ventral dural sac.

    Myelography may be used alone or in combination with CT or MR imaging in the evaluation of patients with suspected spinal stenosis. Similarly, in dysraphism, myelography can demonstrate the caudal displacement of the cerebellar tonsils, the presence of meningocele and the precise position of the spinal cord; however, it is less effective in defining the abnormal nerve roots and the frequently associated lipoma involving the filum terminale.

    The contrast media used for myelography include gas (room air, carbon dioxide, oxygen), water-soluble iodinated media (metrizamide, iopamidol, iohexol, iotrol) and oily contrast media (iophendylate). The water-soluble media produce ideal opacification and demonstrate the subarachnoid space and intrathecal structures faithfully. Iophendylate may cause arachnoiditis when it remains in the subarachnoid space. Also, see myelography.

    DR