A systematic review of intradural disk herniation: A neurosurgeon's perspective

Intradural disk herniation (IDH) refers to the protrusion of the nucleus pulposus into the dural sac. While disk herniation is a relatively frequent condition, the intradural variant is exceptionally rare. Patients diagnosed with IDH often exhibit more pronounced clinical symptoms compared to those with extradural herniations. Establishing a definitive preoperative diagnosis remains challenging, as the pathophysiology and radiological features are not yet fully understood. Differentiating IDH from other intradural extramedullary pathologies, including schwannomas, neurofibromas, meningiomas, or metastatic lesions, can be complex. A systematic review was conducted on the diagnosis and treatment of cervical, thoracic and lumbar IDH, following PRISMA guidelines (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) and retrieving potentially relevant literature from PubMed and Embase. The search strategy included combinations of the terms "transdural" OR "intradural" AND "disc" AND "herniation". Age, sex, symptoms, herniated disk level, history of trauma, location of disk mass, imaging examination, pre- or intraoperative diagnosis and clinical outcomes were studied through the medical records. The type of surgery, the ventral dural defect management and the postoperative leakage of cerebrospinal fluid were also evaluated. One hundred and sixty-one articles involving 285 patients were selected. Cases of IDHs occurred at the lumbar (64.3%), thoracic (21.9%) and cervical (13.8%) levels. The most common level IDH was located at L4-L5 (27.6%). 49 patients exhibited cauda equina syndrome. Only 44 patients (15.4%) were diagnosed as having IDH preoperatively, while most patients were diagnosed intraoperatively. Neurological functions improved variably according to cervical, thoracic and lumbar locations (respectively 2.5%, 5.6% and 21.7%). IDH mostly involves the lumbar spine. Patients with IDH generally experience more severe symptoms than those with extradural disk herniation and have incomplete recovery of postoperative neurological functions. Diagnosing IDH remains challenging given its clinical presentations and radiographic features, and it is likely an underdiagnosed and underestimated condition.