• Vito Fiorenza, Francesco Ascanio, and Ida Di Lorenzo.
• Neurosurgery Department, A.R.N.A.S. Civico-Di Cristina-Benfratelli Hospital, Palermo, Italy. Electronic address: vito.fiorenza1@gmail.com.
• World Neurosurg. 2020 Jul 1; 139: e391-e398.

BackgroundTransdural disc herniations represent about 0.3% of all herniated discs. Preoperative imaging rarely demonstrates this condition. Therefore, diagnosis of transdural disc herniation is usually made intraoperatively. We describe the clinicopathologic features of extremely rare cases of thoracic and lumbar interdural disc herniations mimicking spinal intradural en plaque tumors.MethodsThis is a retrospective case series with a systematic literature review. Clinical presentation, imaging, differential diagnosis, intraoperative microsurgical findings, and possible pathogenesis were reviewed according to published guidelines. All patients underwent a posterior approach for microsurgical excision of disc herniation, but no epidural lesion was found. At intradural exploration, a tumor-like en plaque lesion was discovered. The surface of the lesion was incised, and multiple friable, cartilaginous white-yellow fragments were removed to achieve complete intralesional excision.ResultsThe postoperative course was characterized by progressive neurologic improvement in all cases. In peculiar anatomic (adhesions between the anulus fibrosus, posterior longitudinal ligament, and ventral surface of dura mater) and pathologic (calcified giant disc herniation, spinal canal stenosis, previous lumbar spine surgery) conditions, penetration of disc fragment in the thickness of spinal dura mater can occur.ConclusionsInterdural disc herniations constitute a rare pathologic condition characterized by the migration of the herniated disc in neither the epidural nor the subdural spinal space, but rather in the thickness of the spinal dura mater. Further advances are necessary in neuroradiologic investigations to achieve a correct preoperative diagnosis, which is essential, as spine surgeons must be aware of these rare pathologies.Copyright © 2020 Elsevier Inc. All rights reserved.

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