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The anatomy of the lumbar epidural space was demonstrated in 40 patients by computed tomography (CT) examinations performed after epidural injection of nonionic radiographic contrast material into the sacral caudal canal via percutaneous catheter. Radiologic evaluation of the epidural space was performed to evaluate possible disc hcrniation or other pathologic encroachments on the epidural space. In all 40 patients, the examinations showed the posterior epidural space to be divided by the plica mediana dorsalis and an additional transverse connective tissue plane not previously described. The compartmentalized nature of the space may be, at times, responsible for entrapment and coiling of epidural catheters, despite satisfactory technical performance of catheterization for epidural anesthesia. Thirty-one of 40 patients demonstrated a greater amount of fatty tissue within the junctions of the posterior midline epidural connective tissue structures, producing a bulky triangular-shaped structure which might be an impediment to cath-erization. The divisions of the anterior and posterior epidural spaces are seen to be more complex than previously described.