There are different imaging methods used to image the intervertebral discs of the spine. They include MRI, CT and discography. X-ray provides an imaging of the disc space but does not typically show details of the soft tissues of the disc unless there are calcific changes. Diagnostic discography is performed in an attempt to establish whether a disc is the source of pain. It is often used as part of a pre-operative evaluation to assess whether removal of a disc and/or fusion of a spinal segment is necessary. There are three primary types of diagnostic discography; contrast discography, provocative discography and analgesic discography.
Contrast discography is used to evaluate the structural integrity of the disc. It is performed by injecting a contrast agent into the center portion of the disc. The contrast agent spreads in a variable manner dependent upon the size and integrity of the inside of the disc. In a normal disc the contrast will remain within the central portion of the disc, contained by intact outer supportive rings of tissue (annular fibers). If the contrast material migrates away from the center of the disc it means that there are tears in the supportive fibers.
The normal appearance of the contrast material generally falls into one of four primary categories, which are (1) bilocular, (2) unilocular (3) spherical and (4) rectangular appearances. The normal appearing center of the disc (nucleu) may also be referred to as having a cottonball, unilobular, or a double wafer appearance. The normal nuclear region is usually centrally confined or positioned slightly posterior. Contrast discography must be interpreted carefully as all lumbar discs beyond a certain age will show some degree of degenerative tears or fissuring. If the contrast agent migrates through the outer border of the disc it means that there is one or more complete tears in the disc which extend from the center portion of the disc to the outer border.
Discography is used to evaluate the pattern of tears within the disc (internal disc disruption). Contrast discography is enhanced with the use of computerized tomography (CT) after contrast injection.