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This month’s blog: “Disc Protrusion”. What does it mean?

There are many terms associated with intervertebral disc pathology and understanding what they mean is a critical part of interpreting and clinically correlating MRI findings. The most recent article by Fardon and Milette (2001), reached a consensus on language through some of the most important and influential organizations in the country.

To give you the proper context of who and what was involved in this paper, the authors stated, “The Board of Directors of NASS, and the Executive Committees of both ASSR and ASNR have endorsed this document, as has the Joint Section on Disorders of the Spine and Peripheral Nerves of the American Association of Neurological Surgeons (AANS) and Congress of Neurological Surgeons (CNS), and the CPT and ICD Coding Committee of the American Academy of Orthopaedic Surgeons (AAOS). Endorsement by other North American, European, and international societies is currently pending. This work is being simultaneously posted to the website of the journal Spine and on the ASSR and ASNR websites owing to special arrangements between the editors and publisher of Spine and the American Journal of Neuroradiology (AJNR)” (Fardon and Milette, 2001, p. E93).

Regarding the term “protrusion,” the authors state, “A disc is ‘protruded,’ if the greatest plane, in any direction, between the edges of the disc material beyond the disc space is less than the distance between the edges of the base, when measured in the same plane. The term ‘protrusion’ is only appropriate in describing herniated disc material, as discussed above. Protrusions may be ‘focal’ or ‘broad-based’.  The distinction between focal and broad-based is arbitrarily set at 25% of the circumference of the disc. Protrusions with a base less than 25% (90 degrees) of the circumference of the disc are ‘focal.’ If disc material is herniated so that the protrusion encompasses 25% to 50% of the circumference of the disc, it is considered ‘broad-based protrusion'” (Fardon and Milette, 2001, p. E100).

When talking about disc nomenclature, realize that there are many types of terms that describe “morphology” (what the picture looks like) and those are the terms that are included in the radiologists’ reports and the ones that this paper reviews.  When we talk about the “etiology” (the cause) of the disc pathology, there are only TWO categories, degenerative (slow pathology) and traumatic (instant pathology).  When considering the etiology there are only TWO descriptive terms, disc bulge (degenerative) and disc herniation (traumatic).  All other morphological terms fall under these two categories.  In this case, disc protrusion (morphological or descriptive) falls under the etiological (causation) category of disc herniation.

Reference:

Fardon, D. F., & Milette, P. C. (2001). Nomenclature and classification of lumbar disc pathology. Recommendations of the combined task forces of the North American Spine Society, American Society of Spine Radiology, and American Society of Neuroradiology. Spine, 26(5), E93-E113.