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Anatomy
Much of our early understanding of the anatomy of the subdural space came from the radiological literature. Occasionally, during the performance of myelograms, radiologists found that the contrast was neither in the subarachnoid nor the epidural space but rather in the subdural space. Classically, the space itself is described as a potential space which lies between the dura and the arachnoid mater. It extends from the lower border of the second sacral vertebrae to the floor of the third ventrical and continues for a short distance along the spinal and cranial nerves. The space itself is largest in the cervical area, widest in the lateral and posterior (dorsal) aspects and contains isolated tissue trabeculae, especially posteriorly. In addition, whatever the dynamics of the space are, radiologists noted that fluid injected into this space tend to ascend against gravity.
More recently, some contemporary anatomists using electron microscopy have suggested that the subdural space is not a potential space but rather results from tissue trauma such as the injection of fluid or air or surgical manipulation. This in turn could cleave the meningeal tissues. Regardless of whether or not the subdural space is a potential space or the result of tissue trauma, once it is created it appears to become a more permanent defect. Radiologists have long known that, once they enter the subdural space, it is difficult to subsequently enter the subarachnoid space, either at the time or at a later date.
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