Define the terms used to describe abnormal disc morphology on MR studies

• Annular tear: a disruption of the ligament surrounding the periphery of the disc.

• Bulge: extension of disc tissue beyond the disc space with a diffuse, circumferential, non focal contour.

• Protrusion: displaced disc material extending focally and asymmetrically beyond the disc space. The displaced disc material is in continuity with the disc of origin. The diameter of the base of the displaced portion, where it is continuous with the disc material within the disc space of origin, has a greater diameter than the largest diameter of the disc tissue extending beyond the disc space.

• Extrusion: displaced disc material extending focally and asymmetrically beyond the disc space. The displaced disc material has a greater diameter than the disc material maintaining continuity (if any) with the disc of origin.

• Sequestration: a fragment of disc that has no continuity with the disc of origin. Another commonly used term is free disc fragment. By definition, all sequestered discs are extruded; however, not all extruded discs are sequestered (Fig. 11-4).

A Diffuse disc bulge

B Broad-based protrusion

(or focal disc bulge)

C Focal disc protusion

AP < mediolateral dimension

D Disc extrusion

AP > mediolateral dimension

Disc extrusion

Disc migrates above and/or below parent disc, maintaining continuity with it

F Sequestered disc

Separate from parent disc

Figure 11 -4. Abnormalities of disc morphology. (A) Bulge, (B, C) Protrusion, (D, E) Extrusion, (F) Sequestration. The dashed lines in A and B indicate the vertebral bodies, whereas the solid lines represent the discs. AP, anteroposterior. (From Helms CA, Major NM, Anderson, M, et al., editors. Helms: Musculoskeletal MRI. 2nd ed. Philadelphia: Saunders; 2008, with permission.)

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