PEMLDF occurs infrequently: only 75 cases, including the present case, are reported in the English literature . PEMLDF occurs in middle-aged persons (mean age 53.11 years), possibly owing to the dynamics of spinal degeneration with aging [6–9]. PEMLDF commonly occurs at the upper lumbar levels, especially at the L3/4 level (39.2%). Disc fragments most commonly migrate along a posterior and posterolateral route to the frontal epidural space; the second most common migration corridors are the cranial or caudal (with equal frequency) [10, 11]. Some authors suggest that disc fragments rarely migrate into the posterior epidural region because it requires passing through anatomical barriers such as the posterior longitudinal ligament, peridural or lateral membrane, epidural venous plexus, epidural fat, nerve root, and dura [12–14].
Clinically, PEMLDF can present with symptoms ranging from low back pain to radiculopathy and cauda equine syndrome . Although MRI remains the modality of choice for investigating spinal disorders, PEMLDF can be challenging to diagnose since this type of herniation resembles other epidural pathologies such as abscess, acute hematoma, and malignancy [9, 12, 16, 17]. Malignancy usually produces a solid and rather homogeneous postcontrast enhancement. On the other hand, abscess and hematoma usually have a peripheral rim of enhancement and are associated with an infectious illness, a history of trauma, or antiplatelet drugs.
MRI is the useful imaging tool for the diagnosis of PEMLDF. It appears isointense with the intervertebral disc on T1-weighted images. On the other hands, T2-weighted images reveal a variable intensity of the lesion, with about 80% of all lesions appearing hypointense and the remaining 20% being isointense . On contrast-enhanced MRI images, it appears like a cyst with enhanced rims. However, the MRI appearances of PEMLDF are not specific and they are also found in other posterior epidural lesions. Thus, a definitive diagnosis can at times be made intraoperatively.
Matsumoto et al. used discography and disco-CT to make a definitive diagnosis of intradural lumbar disc herniation , and noted that the contrast medium was not contained in the disc during discography, but also spread intrathecally in a pattern resembling a myelogram. In the present case, clinical history and enhanced MRI findings led us to suspect PEMLDF, and we used discography and disco-CT to make a definitive diagnosis. By performing the discography and disco-CT, we could distinguish PEMLDF from other spinal pathologies, such as malignancy, spontaneous hematoma, or epidural abscess. Furthermore, the discography and disco-CT allowed us to distinguish the L3/4 lumbar-disc herniation from other segments and to understand the whole aspect of the PEMLDF.