The "crumble disc sign": preoperative MRI predictor of intradural lumbar disc extrusion.

Intradural migration of lumbar disc material is a rare complication of disc herniation that can be difficult to diagnose preoperatively. We report a case of recurrent L4-5 disc extrusion in a 64-year-old woman with prior lumbar surgery, in whom preoperative magnetic resonance imaging (MRI) demonstrated a distinctive morphologic pattern consistent with the "crumble disc sign." The intradural component appeared irregular and fragmented within the thecal sac rather than forming a single well-defined mass extension. Recognition of this fragmented intradural morphology on MRI prompted preoperative consideration of intradural disc migration. Surgical exploration confirmed two intradural disc fragments and a dural defect at the L4-5 level. The crumble disc sign reflects fragmented disc material within the cerebrospinal fluid space and may assist in distinguishing intradural disc herniation from solid intradural tumors. This case emphasizes the diagnostic importance of identifying the crumble disc sign on MRI, particularly in postoperative lumbar spines with recurrent symptoms.