Plica mediana dorsalis

aka posteromedian fold of the dura mater
midline posterior epidural ligament between posterior theca and ligamentum flava or spinal lamina in the sagittal plane

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

Although computed tomography and necroscopy have demonstrated some degree of PMD in almost all patients, this is rarely a completely intact membrane

References

Plica Mediana Dorsalis | Anesthesiology | American Society of Anesthesiologists (asahq.org)

pdf (painphysicianjournal.com)

Epidural ligaments | Radiology Reference Article | Radiopaedia.org