Some epidurographic explanations for incomplete epidural analgesia coverage in the absence of a catheter

Study Objective To determine the impact of the plica mediana dorsalis (PMD) on injected contrast media spread in the epidural space. Design Prospective interventional study. Setting Academic medical center. Patients 30 chronic pain patients ranging in age from 37 to 71 years, undergoing epidural steroid injection. Interventions and Measurements Epidurograms were evaluated for the 1) presence or absence of a PMD and 2) bilateral differential density and the extent of contrast spread on either side of the midline, horizontally and vertically. Results The PMD (defined as midline radiolucency in epidurograms) was observed in (80%) 24/30 patients based on the epidurograms that were evaluated. Denser contrast spread on one side was found in (79%) 19/24 patients who had the PMD and in (33%) 2/6 patients who did not have the PMD (P = 0.03). Horizontal and vertical asymmetrical spread of the contrast was observed in (67%) 16 of 24 patients with the PMD and in (50%) 3 of 6 of patients without the PMD in each direction independently. Conclusion The difference in density of contrast spread on either side of the midline carries important clinical implications in understanding the pathogenesis of inadequate epidural analgesia and/or unilateral excessive motor weakness or numbness.