ABSTRACT
A herniated lumbar disc is a very common disease of the spine. However, not all of the disc fragments are located at the expected site. In particular, the ventral epidural space contains many hidden compartments with the potential to hold herniated disc material. We encountered a case of a concealed disc under the peridural membrane, which was very difficult to be identified. The peridural membrane, which is situated below the posterior longitudinal ligament, is a thin glossy membrane surrounding the entire spinal bony canal. The peridural membrane is attached loosely to the median bony septum but not to other part of vertebral body. This potential space between the peridural membrane and bare bone of the vertebral body is called the premembranous space. We report this case to introduce a potential space for disc migration and emphasize the need for a good understanding of the epidural microanatomy.