Concepts of discography

Discography is a procedure that is used to characterize the pathoanatomy/architecture of the intervertebral disc and to determine whether it is a source of chronic spinal pain. It consists of the opacification of the nucleus pulposus of an intervertebral disc to render it visible under radiographs. An implicitly invasive diagnostic test, discography should be used only in those patients with chronic spinal pain in whom one suspects a discogenic etiology [1].

The commonly practiced technical and evaluative components of discography are as follows:

Placement of a sterile needle into the center of the intervertebral disc

Instillation of radiopaque contrast agent to provoke pain

Radiologic assessment of disc morphology

Clinical assessment of the intensity and concordance of evoked pain in relation to baseline pain

Although the evidence supporting the safety and efficacy of discography in the lumbar spine is strong, the evidence for its effectiveness in the thoracic and cervical spine is limited.

The following four classes of discs are identified during a pain-provocative discogram:

Discs that are painful at less than 15 pounds per square inch (psi) above opening pressure

Discs that are painful at between 15 psi and 50 psi above opening pressure

Discs that are painful at more than 50 psi above opening pressure

Disc that are not painful despite pressures above 50 psi that can reasonably be generated

Concepts of internal disc disruption

In 1970, Crock and associates [2] described internal disc disruption (IDD) as a condition marked by alteration in the internal structure and metabolic functions of the intervertebral disc, usually preceded by injuries. Anular tears, including radial and circumferential tears, are the major forms of IDD.

IDD can be diagnosed with the use of computed tomography (CT) in conjunction with discography, a technique referred to as CT discography. A CT scan is performed within 2 hours of intradiscal injection, before the contrast agent has been absorbed. IDD is confirmed by the reproduction of pain on provocative injection of the contrast agent. As a control in the diagnosis of IDD, stimulation of at least one other disc should fail to reproduce pain.

The natural history of untreated single-level IDD confirmed by discography over 3 years was described in a study by Smith and associates [3], who summarized outcomes as follows:

Improved: 68%

Unchanged: 8%

Worsened: 24%

Indications

Cervical discography is indicated for patients with the following features:

Patients with persistent neck and/or cervical radicular pain in whom traditional diagnostic modalities, such as magnetic resonance imaging, CT, and electromyography (EMG), have failed to identify the cause of the pain.

Patients in whom findings identified on traditional diagnostic modalities, such as bulging cervical discs, are equivocal (to determine whether such abnormalities are, in fact, responsible for the pain).

Patients who are to undergo cervical fusion (to help to identify which levels need to be fused).

Patients who have previously undergone fusion of the cervical spine (to help determine whether levels above and below the fusion are causing persistent pain).

Patients in whom traditional imaging techniques cannot distinguish recurrent disc herniation from scar tissue.

The following groups of patients should undergo thoracic discography:

Patients with persistent thoracic radicular or myelopathic pain in whom traditional diagnostic modalities, such as magnetic resonance imaging, CT, and electromyography, have failed to identify the cause.

Patients in whom equivocal findings, such as bulging thoracic discs, are identified by traditional diagnostic modalities (to determine whether such abnormalities are, in fact, responsible for the pain).

Patients who are to undergo instrumentation and fusion of the thoracic spine (in whom discography may help identify which levels need to be fused).

Patients who have previously undergone instrumentation and fusion of the thoracic spine (to help determine whether levels above and below the fusion are responsible for persistent pain).

Patients in whom recurrent disc herniation cannot be distinguished from scar tissue with traditional imaging techniques.

Indications for lumbar discography are as follows:

Further evaluation of demonstrably abnormal discs (to help assess the extent of abnormality or correlation of the abnormality with the clinical symptoms; such symptoms include recurrent pain from a previously operated disc and lateral disc herniation.

Patients with persistent, severe symptoms in whom other diagnostic tests have failed to clearly confirm that a suspected disc is the source of pain.

Assessment of patients in whom surgical intervention has failed, to determine whether there is painful pseudarthrosis or a symptomatic disc in a posteriorly fused segment and to help evaluate possible recurrent disc herniation.

Assessment of discs before fusion to determine whether (1) the discs within the proposed fusion segment are symptomatic and (2) discs adjacent to this segment are normal.

Assessment of candidates for minimally invasive surgical intervention to confirm a contained disc herniation or to investigate dye distribution pattern before chemonucleolysis or percutaneous procedures.

Crock HV [2] have offered the following indications for lumbar discography:

Evaluation of patients with unremitting spinal pain, with or without extremity pain, that has lasted longer than 4 months and has been unresponsive to conservative therapy.

Evaluation of patients with persistent symptoms in whom other diagnostic tests have failed to clearly confirm that a suspected disc is the source of pain.

Evaluation of persistent pain in the postoperative patient whose symptoms may be arising from intervertebral disc degeneration, recurrent herniation, or pseudarthrosis of a spinal fusion.

To determine the number of levels to be fused in spinal surgery and/or to identify the primary symptomatic disc.

In the patient who prima facie has satisfied the criteria for treatment by intradiscal electrothermal therapy (IDET), in whom pain is provoked to detect discogenic pain. In such a patient, CT discography may be undertaken to assess disc morphology to determine whether or not an IDET electrode can be navigated in the disc and, if so, where it should be placed.

For assessment of minimally invasive surgical candidates to confirm contained disc herniations or to investigate dye distribution before chemonucleolysis or other percutaneous decompression procedures.

Contraindications

Absolute contraindications to intervertebral discography are as follows:

Inability or unwillingness of the patient to consent to the procedure.

Inability to assess patient response to the procedure.

Evidence of an untreated localized infection in the procedural field.

Pregnancy.

Relative contraindications to intervertebral discography are as follows:

Allergy to contrast medium, local anesthetic, or antibiotics.

Known bleeding diathesis.

Anticoagulants.

Anatomical derangements, congenital or surgical, that compromise the safe and successful conduct of the procedure.

Known systemic infection.

Complications

Infection is a somewhat common complication of discography. The types of infections seen include discitis, meningitis, subarachnoiditis, subarachnoid or dural and subdural abscess. Of these infections, discitis is the most common with an overall incidence of 0.24% of patients treated and 0.091% of discs involved when using the two-needle technique with or without antibiotics.

Other reported complications include:

Subdural abscess

Spinal cord injury

Vascular injury

Epidural and prevertebral abscess

Intraoperative nausea (2%), convulsion (4%), and severe low back pain (6%)

Aggravation of low back pain (81%) and severe headache (10%) for 1 day after the procedure

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