Disc Protrusion¶

Definition¶

A disc protrusion is a type of herniation in which the base of the displaced disc material at the parent disc is wider than the herniated portion extending beyond the base. The outer annular fibers may be intact (contained) or disrupted, but the overall morphology shows a broad-based, dome-shaped extension.

Imaging Findings¶

MRI¶

Focal disc extension beyond the vertebral margin — the base at the disc level is wider than the apex
Signal usually similar to the parent disc (intermediate T1, variable T2 depending on hydration)
Best seen on axial T2 images for precise characterization
Sagittal T2 shows the craniocaudal extent
May indent the thecal sac or contact nerve roots without displacing them

Key Measurements¶

Mild: <25% of the spinal canal AP diameter
Moderate: 25–50%
Severe: >50%

Clinical Pearl

Disc protrusions are the most common type of herniation and are frequently asymptomatic. The clinical significance depends on the location relative to neural structures and the presence of nerve root contact, displacement, or compression — not merely the presence of the protrusion itself. A small paracentral protrusion contacting the traversing nerve root may cause significant radiculopathy, while a larger central protrusion may be entirely asymptomatic.

Key Points¶

A protrusion has a base wider than the extruded dome — "broad-based" herniation
Most common herniation subtype; frequently incidental
Clinical significance depends on location and degree of neural compression
Best characterized on axial T2 MRI

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. https://pubmed.ncbi.nlm.nih.gov/24768732/
Gaillard F, et al. Disc protrusion. Radiopaedia.org. https://radiopaedia.org/articles/disc-protrusion
Smithuis R, van Loon J. Lumbar Disc Nomenclature 2.0. The Radiology Assistant. https://radiologyassistant.nl/neuroradiology/spine/lumbar-disc-nomenclature-2-0
Bowen BC, Pattany PM. Spine nomenclature. Radsource MRI Web Clinic. https://radsource.us/spine-nomenclature/
Brinjikji W, Luetmer PH, Comstock B, et al. Systematic Literature Review of Imaging Features of Spinal Degeneration in Asymptomatic Populations. AJNR Am J Neuroradiol. 2015;36(4):811–816. https://pmc.ncbi.nlm.nih.gov/articles/PMC4464797/
Brinjikji W, Diehn FE, Jarvik JG, et al. MRI Findings of Disc Degeneration are More Prevalent in Adults with Low Back Pain than in Asymptomatic Controls: A Systematic Review and Meta-Analysis. AJNR Am J Neuroradiol. 2015;36(12):2394–2399. https://pubmed.ncbi.nlm.nih.gov/26359154/
Suthar P, Patel R, Mehta C, Patel N. MRI Evaluation of Lumbar Disc Degenerative Disease. J Clin Diagn Res. 2015;9(4):TC04–TC09. https://pmc.ncbi.nlm.nih.gov/articles/PMC4437133/