A Rare Case of Posteriorly Migrated Sequestered Lumbar Disc Herniation Through the Interlaminar Space

<b>Background and Clinical Significance</b>: Posteriorly migrated lumbar disc herniation [PMLDH] is a rare entity that may present with atypical clinical and radiological features, often mimicking other spinal pathologies. Migration of sequestered fragments through the interlaminar space is exceptionally uncommon, and diagnostic challenges are further amplified in the presence of spinal instability. While MRI and CT are generally sufficient for diagnosis, undetected lesions on preoperative imaging may complicate clinical management. <b>Case Presentation</b>: A 59-year-old male presented with acute low back pain and left-sided radiculopathy. Examination revealed mild motor weakness in ankle dorsiflexion. MRI showed L4-L5 segmental instability with central canal stenosis but no migrated disc fragment. Owing to neurological deficit, decompressive laminectomy with posterior instrumentation was performed. Intraoperatively, a posteriorly migrated sequestered fragment compressing the thecal sac was excised and confirmed as degenerative disc material. Postoperatively, the patient's neurological deficit and radicular pain resolved, with no new complaints at 3-month follow-up. <b>Conclusions</b>: This case highlights an unusual presentation of PMLDH in a patient with lumbar stenosis and spinal instability, undetected on preoperative imaging. Recognition of the biomechanical predisposition at the L3-4 and L4-5 levels is important in understanding such rare migrations. Although literature emphasizes early surgical intervention for PMLDH, our patient required urgent surgery due to neurological deficits rather than a definitive preoperative diagnosis. Further studies are warranted to clarify the relationship between instability and posterior migration.