Delayed caudal migration of a residual intradural disc fragment after endoscopic discectomy for unrecognized intradural disc herniation causing acute cauda equina dysfunction: a case report

Intradural lumbar disc herniation (IDH) is rare, difficult to diagnose preoperatively, and may mimic giant central disc herniation with cauda equina compression. A 71-year-old woman presented with recurrent low back pain and worsening right leg pain/numbness. Imaging showed a giant central L3–4 disc herniation with marked cauda equina compression, but IDH was not diagnosed. During endoscopic decompression and discectomy through a right-sided L3/4 interlaminar approach, a longitudinal ventral dural tear and a free intradural nucleus pulposus fragment were identified, and the visible fragment was removed. Postoperatively, right radicular pain improved, but distal motor dysfunction of the left lower extremity became the main neurological deficit, followed by perineal and saddle hypoesthesia. Emergency MRI showed a lesion posterior to L4. Second-stage open microscopic exploration confirmed and removed a residual intradural nucleus pulposus fragment. Function improved, but motor and bowel recovery remained incomplete at 6 months. IDH should be considered in giant central disc herniation with marked cauda equina compression, even with inconclusive conventional MRI; contrast-enhanced or high-resolution MRI may help. Endoscopic treatment of suspected IDH may be feasible when the dural opening is controlled and visualization is adequate. Continuous irrigation may represent one of several possible contributing factors to displacement of residual intradural fragments. If complete intradural exploration or reliable exclusion of residual fragments cannot be achieved through the endoscopic corridor, timely conversion to microscopic exploration may be considered.