An anatomical study of the intradural space.

We have previously postulated that it is possible to accidentally insert an epidural needle or catheter into the substance of the dura during attempted epidural block, creating an intradural space. It appears that injection of local anaesthetic into an intradural space leads to an initially inadequate neuraxial block but further doses may produce an extensive life-threatening block. In the laboratory, 54 samples of human thoraco-lumbar dura were obtained from six cadavers and prepared for scanning electron microscopy. Images from these dehydrated specimens were assessed for the presence of spaces within the dura, and attempts were made to insert an epidural catheter, under optical microscopy, into the substance of the dura in 32 cases. Electron microscopy revealed the concentric laminae that compose the dura and the presence of artefactual spaces between some of these. It was possible to insert an epidural catheter into the substance of the dura in eight specimens, creating intradural spaces which remained following catheter removal. If this represents the clinical situation, it may help to explain previously reported cases of atypical neuraxial block and their associated radiological findings.