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.