In Medical Articles


Nomenclature and Classification of Disc Pathology

In common medical parlance, doctors have applied their own meanings for disc bulges and disc herniations. The result has been a subjective interpretation of MRI studies, with no method of standardization. Over the last ten years, the American Society of Neuroradiology and the American Society of Spine Radiology have been addressing the deficiencies in the terminology of disc lesions. A publication in the American Journal of Neuroradiology in January 2002 reports the formal adoption of the nomenclature to be used in describing disc lesions.

General Principles:  

It was determined that definitions of disc lesions should be based only on anatomy and pathology, not on clinical findings, symptomatology, or etiology. Definitions of diagnosis should not imply a relationship to the patient’s symptoms or to the patient’s need for specific treatment.


Bulging” is a generalized extension of the disc tissues beyond the edges of the apophyses. Greater than 50 percent of the circumference of the disc, and less than 3 mm. Bulging can be a normal variant, typically at L5-S1, and is not, by definition, a “herniation.” Labeling a disc as “bulging” does not imply etiology, symptoms, prognosis, or the need for treatment.

Herniation” is the “localized displacement of the disc material beyond the limits of the intervertebral disc space.” The “disc space” is the space that is vertically within the vertebral body end-plates, and peripherally by the outer edges of the ring apophyses, exclusive of osteophytic formations. “Localized” means less than 50 percent (180 degrees) of the periphery of the disc, and “generalized” means 50 percent or more of the periphery of the disc. “Herniation” may be in the form of a “protrusion” or an “extrusion.” As with “bulging” discs, the label of “herniated” disc does not imply etiology, symptoms, prognosis, or the need for treatment.

Protrusion” means the disc material extends out beyond the end-plates but the vertical distance does not exceed the distance between the end-plates. In other words, the disc material does not bulge above the upper end-plate or below the lower end-plate.

Extrusion” means that some of the disc material beyond the end-plates is thicker in the vertical direction than the distance between the end plates.  If the extruded disc material has lost complete continuity with the rest of the disc, it is labeled a “sequestration.” If disc material is displaced away from the site of extrusion, it is labeled a “migration.” If posterior disc displacement is constrained by the posterior longitudinal ligament, imaging may appear as “protrusion” on axial sections and an “extrusion” on sagittal sections. In those cases, the disc should be regarded as “extruded.” Where there is a break in the vertebral body end-plate, a herniated disc in the vertical direction through the break should be labeled a “herniation.”

If the displaced material is covered by the annular fibers, the herniation is “contained.” If the nucleus pulposus is outside the annular fibers, the herniation is “uncontained.”