Disc Extrusion¶

Definition¶

A disc extrusion is a type of herniation in which the displaced disc material extends through a defect in the annulus fibrosus such that the herniated portion is wider than its base (neck) at the parent disc level, or extends above or below the disc level in the craniocaudal direction. This represents a more advanced form of herniation than a protrusion.

Imaging Findings¶

Herniated disc — Diagram of a herniated intervertebral disc with nuclear material extending through the annulus fibrosus. (Wikimedia Commons, public domain)

MRI¶

Focal disc extension with a narrower base (neck) than the dome — the key distinguishing feature from protrusion
May migrate superiorly or inferiorly behind the vertebral body (craniocaudal migration)
Signal may differ from parent disc — extruded fragment can have higher T2 signal if acutely hydrated
Often causes significant mass effect on the thecal sac and nerve roots
Best evaluated on sagittal and axial T2 for extent and direction of migration

Subligamentous vs Transligamentous¶

Subligamentous extrusion: disc material passes through the annulus but remains contained beneath the posterior longitudinal ligament (PLL)
Transligamentous extrusion: disc material penetrates through both the annulus and the PLL into the epidural space

Clinical Pearl

Disc extrusions, particularly large ones, have a higher rate of spontaneous resorption than protrusions. Studies show that up to 60–80% of extruded fragments decrease in size or completely resorb over 6–12 months, likely due to an inflammatory/immune response to the exposed nuclear material. This is a strong argument for initial conservative management in patients with extrusions who do not have progressive neurologic deficits or cauda equina syndrome.

Key Points¶

An extrusion has a dome wider than its base, or extends above/below the disc level
Represents a more advanced herniation than protrusion — annular defect is full-thickness
May migrate craniocaudally behind the vertebral bodies
High rate of spontaneous resorption (60–80%) supports conservative management
Urgent surgery only for progressive neurologic deficit or cauda equina syndrome

References¶

Fardon DF, Williams AL, Dohring EJ, Murtagh FR, Gabriel 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. PubMed
Disc extrusion. Radiopaedia.org. Radiopaedia
Ahn SH, Ahn MW, Byun WM. Effect of the transligamentous extension of lumbar disc herniations on their regression and the clinical outcome of sciatica. Spine (Phila Pa 1976). 2000;25(4):475-480. PubMed
Weishaupt D, Zanetti M, Hodler J, Boos N. MR imaging of the lumbar spine: prevalence of intervertebral disk extrusion and sequestration, nerve root compression, end plate abnormalities, and osteoarthritis of the facet joints in asymptomatic volunteers. Radiology. 1998;209(3):661-666. PubMed
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. PMC
Yu P, Mao F, Chen J, et al. Characteristics and mechanisms of resorption in lumbar disc herniation. Arthritis Res Ther. 2022;24(1):205. PMC
Kesikburun B, Eksioglu E, Turan A, Adiguzel E, Kesikburun S, Cakci A. Spontaneous regression of extruded lumbar disc herniation: Correlation with clinical outcome. Pak J Med Sci. 2019;35(4):974-980. PMC