Talk:Subdural space

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Quite incorrect. 'The SDS (sub-dural space) is a naturally-occuring space', maybe a potential one, between the outermost layer of arachnoid, and the inner layer of the dura.Normally the arachnoid is kept in contact with the dura partly by the hydrostatic pressure of the CSF within, partly by a surface-tension effect between the two membranes, and also by their proximity as they converge along the course of the issuing spinal nerve roots, (and probably the cranial nerves also). Those who remember their embryology will be aware that the arachnoid is derived from the neuro-ectoderm, and it is therefore part of the nervous system, whereas the dura is derived from the primitive mesoderm, which also gives rise to connective tissue, bones, muscles and joints. Nerve roots grow out from the neuro-ectodermally derived central nervous tissue towards the peripheral tissues as they form, and all peripheral nerves have a covering of connective tissue, from which they are separated by a peri-neural lymphatic space, which connects to the bodies' general lymphatic space, including the sub-dermal lymphatic network, as was occasionally demonstrated during lymphangiography. My interest in this space started in 1958, because from time to time a myelogram would go wrong because the contrast was not correctly inserted into the subarachnoid space. The resulting appearances were difficult to interpret, and rarely of diagnostic value. However, in a series of case it was possible to discern that the myodil could be either extradural, intra-arachnoid, or subdural. Usually it was a mixture of all three! Occasionally, however, it would be totally subdural, in which case it would not be gravitationally dependent, as would subarachnoid myodil, and would spread more extensivel along the spinal canal. If the patient was re-examined after a few days it would be found that the myodil had spread along the issuing spinal nerves in the lumbar region, and down the sciatic nerve. One one occasion I watched the patient'cough' it along the nerve, and by taking follow-up films I saw it reach the back of the knee, after some weeks. This spread was not visible with the water-soluble media which replaced the oily medium, because of their rapid absorption. To better understand the radiographic appearences I carried out some dissections on a section of lumbar spine taken from a cadaver. Initially I could not find the arachnoid, until I realised that it had collapsed down around the cauda equina. Following this discovery I was able to inflate the arachnoid within the dura, by tying off the dural sac at the top and bottom of the specimen. Radiographs were then taken, using barium sulphate as a contrast medium, which allowed a direct visualisation of its presence and position, as well as x-ray appearances.

There are a number of important implications relating to the continuity of the SDS with the general lymphatic space. Whilst an intact arachnoid might present a formidable barrier to entry of foreign bodies, or substances, were this integrity to be impaired, either from a congenital fault, or through an acquired trauma, it might allow unimpeded access to the nervous system by virus or bacteria, or repeated escape of CSF into the lymphatic system, with allergic implications. It is postulated that some of the unexplained ailments of the nervous sustem might be related to this. This work was originally presented to the Royal College if Radiologists' meeting in Stoke on Trent in 1975 —The preceding unsigned comment was added by Alanofmaesyrhedydd@btinternet.com (talk • contribs).