Appearance of plica mediana dorsalis during epidurography.

To the Editor: The plica mediana dorsalis (PMD) is thought to be a band of connective tissue, which divides the epidural space at the dorsal midline. Existence of the PMD has been controversial since its first description in 1963 (1). The PMD has been regarded as a potential cause for unilateral epidural blockade (2, 3). For purpose of discussion, we present a case of a patient who presented for an interlaminar lumbar epidural steroid injection. Under epidurography, a structure similar in appearance to a PMD was identified, but it did not interfere with bilateral contrast flow. The patient was a 47-year-old male, 114 Kg in weight and 1.83 m tall, with symptoms consistent with left L5 radiculitis. MRI scan performed two months prior to presentation showed previous L4-5 right hemilaminectomy, and left-sided L4-5 disc herniation. He was scheduled for an interlaminar epidural steroid injection at the left side of the L5-S1 interspace. After informed consent was obtained and a “time-out” was conducted, the patient was placed in the prone position. The L5-S1 interspace was optimized under anteriorposterior (AP) view with fluoroscopy. Skin prep and drape were performed. Local anesthetic infiltration was performed with 1% lidocaine [AstraZeneca LP, Wilmington DE], an 18 g 9 cm Tuohy needle was directed toward the left side of the L5-S1 interspace using AP (Fig. 1) and lateral fluoroscopic images. A 5 cc ground glass syringe containing 3 cc normal saline and a 1 cc air bubble was used for loss of resistance Appearance of Plica Mediana Dorsalis during Epidurography