Adhesive arachnoiditis represents the most severe form of an inflammatory disease process involving the pia-arachnoid membranes of the brain and spinal canal. It is produced by an inflammatory reaction to the presence of foreign body substances in the subarachnoid space. These can be natural such as blood or bacteria or iatrogenic such as iophendylate or water soluble substances being used for the purpose of diagnostic myelography

Myelography (myelo-spinal cord, graphy-measurement of) is a well-established and important means of studying the spinal canal by the introduction of various substances into the subarachnoid space so the space can be visualized on x-ray. The first myelograms , introduced by Dandy in 1919, were performed following the injection of air. Air myelograms were difficult to perform and to interpret. Because of this Lipiodol, the first of the iodinated oil agents, was introduced by Sicard and Forestier in 1922. The rather dramatic toxicity of Lipiodol in animals and humans led to the search for alternatives. In this regard thorium dioxide (a radioactive substance) was introduced in 1923 and iophendylate in 1942. Iophendylate was created as a substitute for Lipiodol but, quite remarkably, its toxicity was similar to, although not as severe as Lipiodol. How iophendylate became a universal contrast agent used for routine full-column myelography without ever having been officially approved for such is, in itself, a remarkable event. Although never officially acknowledged, the toxicity of iophendylate did become evident to many physicians around the world. In Sweden efforts were initiated to develop water-soluble alternatives in the late 1940s. The process of this development was slow and difficult because the early water-soluble agents were highly irritating to the nervous system and meninges producing hypotension, spasm, seizures,.and even more serious adverse consequences. Even with this knowledge the desire to avoid the problems associated with oil myelography was, in some countries, so great that clinicians exercising the "risk versus benefit" philosophy chose myelography with water-soluble substances under general anesthesia in order to avoid exposing their patients to the known problems related to iophendylate

In 1978 Dimer-X (meglumine iocarmate), developed in 1972, became the first water-soluble myelographic contrast agent released for use in the United States. Because of a number of acute reactions (i.e. severe hypotension) it was officially withdrawn from use. In the series of patients at the Institute for Low Back and Neck Pain in which Dimer-X was used it was found that protective premedication with dexamethasone and Valium (diazepam) effectively blocked the adverse effects (because Dimer-X was withdrawn this study was never published). Amipaque (metrizamide), which was first developed in 1973, then became the water-soluble agent of choice in the United States. With the subsequent development of the next generation of non-ionic water-soluble contrast agents, iopamidol (1985), iohexal (1985) and iotrolan (1990), the patient risk factors were further decreased and these substances then became the universal standard

Although the true incidence and prevalence of adhesive arachnoiditis, and its worldwide relationship to patient disability and incapacitation has never really been properly documented reasonable estimates based on accurate observation can be made. Incidence is quite high with the oil based myelographic agents. It is quite small with the water-soluble contrast agents, particularly with the non-ionic agents. This is not to say that the water-soluble agents haven't been associated with significant adverse reactions; their problems, however, have been of a different nature and typically reflect acute nerve cell and meningeal reaction. These reactions tend to be minimal but if the wrong water-soluble agents, or the wrong concentrations of agent, are administered there can be serious consequences such as permanent neurologic injury or death.

It is important to understand that myelography has never really been a great diagnostic study. Even with modern non-ionic agents it is still an invasive test limited showing only the subarachnoid space. All myelography introduces foreign body substances into the most sensitive area of the human body, the subarachnoid space. Myelography is a poor means of demonstrating many important entities such as pathology in the foraminal zone of the vertebral canal. Because of this lateral nerve entrapment due to lateral spinal stenosis has often been missed by clinicians and remains the most common reason for failed back surgery. One has only to compare myelography to a non-invasive, modern high-resolution, fast spin-echo MRI to appreciate the full meaning of this comparison. Before the advent of CT and MRI imaging there were many clinicians in the United States who believed, in regard to oil myelography that "no myelography" and more "exploratory surgery" was in the best interest of their patients. Non-ionic water-soluble agents have become the myelographic "gold standard" and continue to be valuable and important diagnostic tools (particularly when used in conjunction with CT and MRI imaging). Although myelography has now, to a great extent, been replaced by CT and MRI it remains a needed diagnostic study.

Charles V. Burton, M.D.
Senior Medical Director
The Institute for Low Back and Neck Care
Minneapolis, Minnesota, U.S.A.
April 3, 1998