Disc Sequestration¶

Definition¶

A disc sequestration (free fragment) is a type of disc herniation in which a portion of the disc material has completely separated from the parent disc and migrated within the spinal canal. The sequestered fragment has no remaining continuity with the disc of origin.

Imaging Findings¶

MRI¶

Free fragment in the epidural space, separate from the parent disc — this is the defining feature
Often migrates superiorly or inferiorly behind the vertebral body; can migrate considerable distances
Signal may differ from parent disc — fragment may be lower T2 signal (dehydrated) or higher (inflammatory edema surrounding it)
Peripheral enhancement with gadolinium is common (inflammatory granulation tissue around the fragment)
May be mistaken for an epidural tumor or abscess if the relationship to the parent disc is not recognized

Key Imaging Clues¶

Disc-level defect at the parent disc (gap where fragment originated)
Epidural mass not contiguous with any disc level
Peripheral enhancement on post-contrast images
Low T2 signal core with surrounding high T2 edema

Clinical Pearl

Sequestered fragments have the highest rate of spontaneous resorption of all herniation subtypes — the immune system recognizes the exposed nuclear material as foreign and mounts an inflammatory resorption response. However, sequestrations can also cause severe acute radiculopathy or cauda equina syndrome due to their mass effect. A free fragment compressing the cauda equina with bladder dysfunction is a surgical emergency regardless of resorption potential.

Key Points¶

Sequestration = free fragment completely separated from the parent disc
Can migrate considerable distances within the spinal canal
Highest rate of spontaneous resorption among herniation subtypes
May mimic epidural tumor or abscess — gadolinium shows peripheral enhancement
Cauda equina syndrome from a large sequestration is a surgical emergency

References¶

Fardon DF, Williams AL, Dohring EJ, Murtagh FR, Rothman SL, Sze GK. Lumbar disc nomenclature: version 2.0: Recommendations of the combined task forces of the North American Spine Society, the American Society of Spine Radiology and the American Society of Neuroradiology. Spine J. 2014;14(11):2525-2545. https://pubmed.ncbi.nlm.nih.gov/24768732/
Disc sequestration. Radiopaedia.org. https://radiopaedia.org/articles/disc-sequestration
Li ST, Zhang T, Shi XW, Liu H, Yang CW, Zhen P, Li SK. Lumbar disc sequestration mimicking a tumor: Report of four cases and a literature review. World J Clin Cases. 2022. https://pmc.ncbi.nlm.nih.gov/articles/PMC8968809/
Zeng Z, Qin J, Guo L, et al. Prediction and Mechanisms of Spontaneous Resorption in Lumbar Disc Herniation: Narrative Review. Spine Surg Relat Res. 2023. https://pmc.ncbi.nlm.nih.gov/articles/PMC11165499/
Hu C, Lin B, Li Z, Chen X, Gao K. Spontaneous regression of a large sequestered lumbar disc herniation: a case report and literature review. J Int Med Res. 2021;49(11). https://pmc.ncbi.nlm.nih.gov/articles/PMC8649452/
Stadnick ME. Free Disc Fragment. Radsource MRI Web Clinic, January 2004. https://radsource.us/free-disc-fragment/
Smithuis R. Lumbar Disc Nomenclature 2.0. The Radiology Assistant. https://radiologyassistant.nl/neuroradiology/spine/lumbar-disc-nomenclature-2-0