Revisiting 'idiopathic' spinal cord herniation: Evidence for an acquired pathogenesis from spinal anterior dural dissection.

PURPOSE: Idiopathic spinal cord herniation (iSCH) is a rare cause of myelopathy characterized by protrusion of the spinal cord through a focal defect in the dura mater. Its pathogenesis remains poorly understood. In this study, we present evidence supporting an acquired mechanism involving dural dissection. METHODS: We conducted a single-center case series of patients diagnosed with iSCH, with a focus on clinical and radiological features that provide insight into the condition's etiology and natural history. RESULTS: We identified 18 patients with iSCH, including 15 who underwent surgical treatment. In 14 patients (78%), the initial magnetic resonance imaging (MRI) demonstrated a longitudinal cerebrospinal fluid (CSF) collection along the anterior aspect of the dural sac, consistent with spinal anterior dural dissection. Six patients initially presented with clinical features of spontaneous intracranial hypotension. In three of these cases, serial MRI demonstrated progressive herniation of the spinal cord through the dural defect over time. A histological analysis of the dystrophic herniated tissue in one patient retrieved fatty and gliotic degeneration, further supporting an acquired mechanism. CONCLUSION: Our findings support the hypothesis that iSCH might represent an acquired complication of spinal anterior dural dissection rather than a congenital abnormality of the spinal cord or dura. Accordingly, we propose reclassifying iSCH within the spectrum of duropathies, with spontaneous intracranial hypotension as a potential initial manifestation.