BACKGROUND: Unilateral spread of local anesthetics has been reported in approximately 21% of epidural blocks. Plica mediana dorsalis (PMD) is a connective tissue structure that divides the epidural space along the dorsal midline. While unilateral blocks are the most common complication observed in these cases, there have been a few instances involving PMD where a bilateral distribution of the contrast and injectate was visualized under fluoroscopy.

CASE REPORT: We present 2 cases involving PMD, each showing different contrast distributions upon epidurography.

CONCLUSIONS: PMD is a potential cause of unilateral epidural blocks. It could present as a complete or partial membrane, resulting in variations in contrast/local anesthetic distributions. Repositioning the needle and bilateral blocks help achieve the desirable outcome in patients with an intact membrane. In contrast, a thin PMD membrane could result in a partial rupture and the spread of the medications bilaterally.

KEYWORDS: PMD, Plica mediana dorsalis, unilateral epidural block