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

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.  

Multi-modal Real Time Assessment

Discography is an invasive procedure associated with some risks. When it is performed the examiner should try to obtain as much information about the health and role of the disc as possible. Multiple factors can be evaluated during discography. Real time multi-recording of the data helps the examiner determine the significance of the results. This type of testing is called real time multi-modal data acquisition.  The following areas can be evaluated; pressure gradients of contrast injection, motion X-ray (fluoroscopic) images of contrast agent placement and movement, recording of the patient’s facial expressions, and the acquisition of a verbal description of what the patient did or did not experience.

MRI has replaced discography as the safest and most revealing study for the structural assessment of disc health and disease.  Contrast discography will only detect tears inside the disc that communicate with the center portion of the disc where the contrast agent is injected. The primary benefit of discography is that it provides a method for assessing whether a disc is causing pain.

Provocative and Analgesic Discography

Provocative discography refers to the approach used during diagnostic discography to help identify the role of one or more discs in back pain. It is a technique, which is used in an attempt to reproduce discogenic symptoms by introducing chemical stimuli and/or by altering the pressure within the disc.  The placement of the needle, the pressure of the fluid introduced, and the pro-inflammatory chemical reaction within the disc can potentially reproduce pain in an already compromised, symptomatic intervertebral disc.  During the procedure an anesthetic agent can then be injected into the symptomatic disc.  If the application of the analgesic agent provides rapid relief of discomfort or pain it confirms that the tested disc is contributing to back symptoms.

Provocative discography should be performed under motion X-ray (fluoroscopic) guidance in an attempt to reduce potential complications.  The procedure should be performed in a surgical suite with a mobile C-arm fluoroscopic unit.

Who is a Candidate for Discography

Discography should only be considered if the patient has intractable back pain, which has failed to respond to an adequate trial of non-operative treatment methods. Discography may also be considered as part of the assessment of failed back surgery to determine if there may be a painful pseudoarthrosis or symptomatic disc in a posterior fused segment. It may also be used to help confirm the precise level of the spine requiring fusion. The use of discography may be used to guide minimally invasive disc procedures such as nucleoplasty or Intra discal electro thermocoagulation (IDET).