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Epidural anatomy: new observations

1998; Springer Science+Business Media; Volume: 45; Issue: S1 Linguagem: Inglês

10.1007/bf03019206

1496-8975

Quinn H. Hogan,

Cardiac, Anesthesia and Surgical Outcomes

Why study epidural anatomy? The epidural space is a site of therapeutic ministrations at an accelerating pace. Anaesthetists insert needles and catheters there for the deposition of a growing variety of anaesthetic and analgesic agents. Electrical leads are placed for spinal cord stimulation in chronic pain states, and endoscopic methods are being developed for visual examination of the epidural contents. Occasionally, the epidural space is the site of complications caused by these various efforts, such as haematomas or abscess. I believe successful and safe use of this anaesthetic venue is aided by an accurate understanding of the contents of the spinal canal. It is easy to imagine that gross anatomy has been completely explored and little remains unknown. I have become convinced, however, that there are important defects in the epidural anatomy we have been taught. Several factors may explain our collective comfort with the imperfections of artists renditions of anatomy. First, good art is appealing to look at and real anatomy is typically much less orderly. It often isn't evident how much assumption and imagination goes into medical illustration. Second, real anatomy, as described below, is complex, and, therefore, less easily presented and taught. Third, anatomy of the epidural space is not a hot topic in anaesthesia research, and isn't very interesting to others. For surgeons, it is only a pathway to the bones, disc, nerves and cord. The most important impediment to better understanding of the epidural space is that its a particularly hard place to study. The walls of the spinal canal are as tough and impenetrable a barrier as can be found in the body. However, the contents are frail. Subtle pressures including the cerebrospinal fluid (CSF) pressure and the slightly subatmospheric tissue pressure in the epidural space deploy the semifluid contents and direct fluid distribution. Opening the space by dissection, even in a living subject during surgery, alters these pressures and destroys natural tissue relationships. Investigations have employed injection, either of contrast for radiographic imaging, 1,2 of resin for examination after dissection, 3 or of air to create a space for endoscopic viewing. 4 All these approaches distort the native anatomy due to displacement of epidural contents. New methods have allowed examination without artifact. Cryomicrotome sectioning s,6 is a means of producing high resolution images of anatomical material after freezing, which prevents tissue movement. Magnetic resonance imaging (MR/) has increased in resolution steadily over the past decade, and provides in vivo comparison and confirmation. These approaches, combined with histologic study 7 and computerised tomographic (CT) imaging of the passage of catheters and distribution of solution, reveal an epidural space that is complex in structure, unpredictable during instrumentation, but accommodating in clinical effect.