title: Unintentional subdural placement of epidural catheters during attempted epidural anesthesia: an anatomic study of spinal subdural compartment.
abstract: BACKGROUND
  Although infrequent, subdural block is a complication of epidural anesthesia with obvious implications. Knowledge of the spinal subdural compartment (dura-arachnoid interface) may help elucidate controversies arising from evidence that subdural catheter placement is feasible and may be difficult to identify clinically.
  
  
  METHODS
  Samples of arachnoid lamina obtained during in vivo lumbosacral surgery (n = 4) and from cadavers (n = 6) were obtained and prepared for transmission electron microscopy and scanning electron microscopy. Subdural spaces were artificially produced in suitable samples, and an epidural catheter was inserted between the arachnoid and dura to compare the dimensions of meninges in relation to epidural catheters.
  
  
  RESULTS
  Scanning electron microscopy of the dural sac showed areas of continuity between the arachnoid lamina and dura mater and other parts with both membranes separated by a subdural space. Transmission electron microscopy allowed the study of such border zones, where alternating cellular and collagen layers could be seen. A layer rich in collagen fibers and some fibroblasts separated arachnoid and neurothelial cells (dural border cells). Few specialized membrane junctions were found among cells adjacent to collagen fibers. Dura mater had an average thickness of 260 to 400 μm, with a dural lamina of approximately 4 to 6 μm. In areas where the arachnoid appeared separated from the dural lamina, its thickness measured 35 to 45 μm. Catheters with a diameter of 700 μm were successfully inserted inside the subdural space, between the dura mater and the arachnoid lamina.
  
  
  CONCLUSIONS
  Dura mater and arachnoid layers act as a single unit but may be pulled apart by traction forces during cadaver processing of the dural sac or in vivo placement of catheters. This generates subdural spaces, either parallel or concentric, because of the minimal resistance offered by the tissue, which may be explained by its few specialized membrane junctions.
authors: Department of Clinical Medical Sciences and Applied Molecular Medicine Institute, CEU San Pablo University School of Medicine, Madrid, Spain. miguelangel.rei@terra.es
authors: Miguel Angel
authors: MA
authors: Reina
authors: Clive B
authors: CB
authors: Collier
authors: Alberto
authors: A
authors: Prats-Galino
authors: Anna
authors: A
authors: Puigdellívol-Sánchez
authors: Fabiola
authors: F
authors: Machés
authors: José Antonio
authors: JA
authors: De Andrés
mesh_terms: D000328:Adult; D000767:Anesthesia, Epidural / Q000009:adverse effects* / Q000295:instrumentation*; D002408:Catheters, Indwelling / Q000009:adverse effects; D004388:Dura Mater / Q000601:surgery / Q000648:ultrastructure; D006801:Humans; D019300:Medical Errors; D008875:Middle Aged; D013355:Subdural Space / Q000601:surgery / Q000648:ultrastructure*