Figure 2. (A) Computed tomographic image after 0.4 ml of contrast material is injected in a 55-yr-old woman with an epidural catheter tip in the posterior epidural space (arrow). Multiple air bubbles (black areas) are evident in the spinal canal and along the spinous process. (B) After an additional 4 ml is injected, contrast material outlines the posterior epidural fat (F) and passes predominantly to the left of the dura (to the right in the image). (C) After an additional 10 ml is injected, contrast material passes out both foramina, especially the left (large straight arrow) and also accumulates anterior to the dura. Air bubbles produce no impediment. Tethering of the posterior dura produces a fold (curved arrow). An epidural tissue membrane directs a layer of contrast material (small arrow) along the outer aspect of the dural sac, distinct from the larger posterior collection.