LAUSR

BACKGROUND Transdural disc herniations (TDHs) represent about 0.3% of all herniated discs. Preoperative imaging rarely demonstrates this particular condition. Therefore, diagnosis of TDH is usually made intraoperatively. We describe the clinicopathologic features of extremely rare cases of thoracic and lumbar interdural disc herniations (IDHs) mimicking spinal intradural en-plaque tumors. METHODS This is a retrospective case series with a systematic literature review. The clinical presentation, imaging, differential diagnosis, intraoperative microsurgical findings and possible pathogenesis were reviewed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. All patients underwent posterior approach for microsurgical excision of disc herniation, but no epidural lesion was found. At intradural exploration we discovered a tumor-like en-plaque lesion. Surface of the lesion was incised and multiple friable, cartilaginous white-yellow fragments were removed until complete intralesional excision. RESULTS Post-operative course was characterized by progressive neurological improvement in all cases. In particular anatomical (adhesions between the annulus fibrosus, PLL, and ventral surface of dura mater) and pathological conditions (calcified giant disc herniation, spinal canal stenosis, previous lumbar spine surgery) penetration of disc fragment in the thickness of spinal dura mater can occur. CONCLUSIONS IDHs constitute a rare pathologic condition characterized by the migration of the herniated disc neither in the epidural nor in subdural spinal space, rather in the thickness of the spinal dura mater. Further advances are necessary in neuroradiological investigations to achieve a correct pre-operative diagnosis, that is essential to spine surgeon who must be aware about these rare pathologies.