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

New developing or aggravation of previous low back pain and microtrauma of the intervertebral disc

Spinal headache, paraspinal muscle pain, and contusion

Intrathecal hemorrhage

Nerve root damage

Vasovagal reactions

Preoperative preparation

The characteristic patient complaints indicating discography are as follows:

Weight-bearing difficulty

Unexplained cause or undetermined level of suspected discogenic axial or radicular pain that needs interventional pain management

Imaging diagnosis consists of the demonstration of IDD or intervertebral herniation on magnetic resonance imaging.

Medication given before discography consists of antibiotics for prophylaxis against infection (Tables 13.1 and 13.2).

Table 13.1 Dosages of Antibiotics Recommended for Prophylaxis in Patients Undergoing Spinal Surgery

* Administered at 4-hour intervals (8-hour intervals for glycopeptides and gentamicin) for surgical procedures lasting ≥4 hours (or ≥8 hours if patient is receiving a glycopeptide/aminoglycoside regimen). Gentamicin and vancomycin must be used with caution in patients who have impaired renal function or who are otherwise at risk of toxicity from these drugs. From Brown EM, Pople IK, de Louvois J, Hedges A, Bayston R, Eisenstein SM, Lees P. British Society for Antimicrobial Chemotherapy Working Party on Neurosurgical Infections. Spine update: prevention of postoperative infection in patients undergoing spinal surgery. Spine (Phila Pa 1976). 2004;29(8):938-45.

Table 13.2 Antibiotic Penetration into Discs

Procedures

Cervical Discography

Cervical discography is performed as follows:

1. The patient’s written informed consent is obtained.

2. The patient is placed supine with the neck in a neutral position.

3. The anterior right side of the neck is usually chosen for needle entry, because the esophagus tracks to the left as it descends through the neck.

4. The skin of the anterior neck is prepared with antiseptic solution.

5. CT or fluoroscopic views are taken through the discs to be imaged, and the relative positions of the carotid artery, esophagus, trachea, nerve roots, and spinal cord are noted.

6. A skin wheal of local anesthetic is placed at the medial border of the sternocleidomastoid muscle at the level to be evaluated.

7. A 10-cm, 22-gauge styletted needle is advanced toward the superior margin of the vertebral body just below the disc of interest, with care taken to avoid the carotid artery, jugular vein, trachea, and esophagus (Fig. 13-1).

8. After the needle impinges on bone, the depth at which bone contact is made is noted, and the needle is withdrawn into the subcutaneous tissues and then advanced in a more superior trajectory into the anterior disc anulus.

9. The needle is advanced by increments into the nucleus.

10. Water-soluble contrast medium suitable for intrathecal use is slowly injected through the needle into the disc in a volume of 0.2 to 0.6 mL.

11. The resistance to injection should be noted, because an intact disc offers resistance at these volumes. Simultaneously, the patient’s pain response during injection is noted. The site of the patient’s pain and its quality and similarity to the ongoing clinical symptoms are evaluated (Figs 13-2, 13-9, 13-10).

12. Injection for pain provocation should continue until pain is produced, contrast medium escapes from the disc, the volume of injection reaches 0.6 mL, or firm resistance to the injection is encountered.

Figure 13–1 Technique of cervical discography.

Figure 13–2 Assessment sheet for disc stimulation.

Thoracic Discography

Thoracic discography is performed as follows:

1. The patient’s written informed consent is obtained.

2. The patient is placed prone with a pillow under the lower chest to slightly flex the thoracic spine.

3. CT or fluoroscopic views are taken through the discs to be imaged, and the relative positions of the pleural space, lung, ribs, nerve roots, and spinal cord are noted.

4. The spinous process of the vertebra just above the disc to be evaluated is palpated.

5. At a point just below and 1.5 inches lateral to the spinous process, the skin is prepared with antiseptic solution, and the skin and subcutaneous tissues are infiltrated with local anesthetic.

6. A 16-cm, 22-gauge, styletted needle is introduced through the skin under CT or fluoroscopic guidance, the target being the middle of the disc of interest (Fig. 13-3). Given the proximity of the somatic nerve roots, paresthesia may be elicited in the distribution of the corresponding thoracic paravertebral nerve. If this occurs, the needle should be withdrawn and redirected slightly more cephalad. The needle is again advanced in increments under CT or fluoroscopic guidance, with care taken to keep the needle trajectory medial, to avoid causing pneumothorax.

7. The needle is advanced increments into the central nucleus. Sequential CT scanning or fluoroscopy is indicated to avoid advancing the needle completely through the disc and into the thoracic spinal cord and to avoid allowing the needle to track too laterally into the pleural cavity.

8. Water-soluble contrast medium suitable for intrathecal use is then slowly injected through the needle into the disc in a volume of 0.2 to 0.6 mL.

9. The resistance to injection should be noted, because an intact disc offers resistance at these volumes. Simultaneously, the patient’s pain response during injection is noted. The site of the patient’s pain and its quality and similarity to the ongoing clinical symptoms are evaluated (see Fig. 13-2).

10. Injection for pain provocation should continue until pain is produced, contrast medium escapes from the disc, the volume of injection reaches 0.6 mL, or firm resistance to the injection is encountered.

Figure 13–3 Technique of thoracic discography.

Lumbar Discography

Lumbar discography is performed as follows:

1. The patient’s written informed consent is obtained.

2. The patient is placed prone with a pillow under the abdomen to slightly flex the lumbar spine.

3. CT or fluoroscopic views are taken through the discs to be imaged, and the relative positions of the lung, ribs, aorta, vena cava, kidneys, nerve roots, and spinal cord are noted.

4. The spinous process of the vertebra just above the disc of interest is palpated. At a point just below and 1.5 to 3 inches lateral to the spinous process, the skin is prepared with antiseptic solution, and the skin and subcutaneous tissues are infiltrated with local anesthetics.

5. A 16-cm, 22-gauge, styletted needle is introduced through the skin under CT or fluoroscopic guidance toward the target, the middle of the disc to be imaged. Given the proximity of the somatic nerve roots, paresthesia may be elicited in the distribution of the corresponding lumbar paravertebral nerve. If this occurs, the needle should be withdrawn and redirected slightly more cephalad (Fig. 13-4).

6. The needle is advanced in increments into the central nucleus. Sequential CT scanning or fluoroscopy is indicated to avoid advancing the needle completely through the disc and into the lower limits of the spinal cord or cauda equina. The clinician must also take care not to allow the needle to track too far laterally into the lower pleural or the retroperitoneal space.

7. Water-soluble contrast medium suitable for intrathecal use is slowly injected through the needle into the disc in a volume of 0.5 to 3 mL.

8. Resistance to injection should be noted, because an intact disc offers resistance at these volumes. Simultaneously, the patient’s pain response is noted. The site of the pain and its quality and similarity to the ongoing clinical symptoms are evaluated (see Fig. 13-2).

9. Injection for pain provocation should continue until pain is produced, contrast medium escapes from the disc, the volume of injection reaches 3 mL, or firm resistance to the injection is encountered.

Figure 13–4 Technique of lumbar discography.

Related anatomy and physiology

The anatomy and physiology related to the performance of discography are listed in Table 13.3 and illustrated in Figures 13-1 and 13-3 through 13-6.

Table 13.3 Anatomic Structures Visualized by Discography

See Figs 13-1, 13-4, and 13-5.

Figure 13–5 Innervation of an intervertebral disc.

Figure 13–6 Diagrammatic comparison of in vivo loads (disc pressures) in the third lumbar disc during various activities.

Interpretation of discography

. Probable discogenic pain

.

Data from Bogduk B: Proposed discography standards. ISIS Newsletter, Volume 2, Number 1. Daly City, California, International Spinal Injection Society, 1994. pp 10-13.Derby R: A second proposal for discography standards. ISIS Newsletter, Volume 2, Number 2. Daly City, California, International Spinal Injection Society, 1994. pp 108-122.

Table 13.9 Classification of CT Discographic Findings

Data From Bernard TN Jr: Lumbar discography followed by computed tomography. Refining the diagnosis of low-back pain. Spine 15: 690-707, 1990.Sachs BL, Vanharanta H, Spivey MA, Guyer RD, Videman T, Rashbaum RF, Johnson RG, Hochschuler SH, Mooney V. Dallas discogram description. A new classification of CT/discography in low-back disorders. Spine (Phila Pa 1976). 1987 Apr;12(3):287-94.

Table 13.10 Patterns of Pain Provocation for Positive Discograms

Data from Ohnmeiss DD, Vanharanta H, Ekholm J. Degree of disc disruption and lower extremity pain. Spine (Phila Pa 1976). 1997 Jul 15;22(14):1600-5.

Figure 13–7 Modified Dallas discogram scheme for the classification of anular tears on CT discography. Internal disc disruption can be graded in five levels as follows. Grade 0, normal disc. In grade 1, the contrast agent spreads radially along a fissure to the inner third of the anulus. In grade 2, the contrast agent extends into the middle third. In grade 3, the contrast agent extends into the outer third of the anulus fibrosus to an extent of less than 30 degrees of the disc circumference. When a grade 3 tear dissects the outer third of anulus fibrosus for more than 30 degrees, it is classified as grade 4. A tear involving the full thickness of the anulus with extra-anular leakage is grade 5.

Figure 13–8 The five types of discogram and the stages of disc degeneration they represent.

Figure 13–9 Cervical discogenic pain mapping. A, Body region pain diagram. B, Numerical coordinates for the body regions.

(Modified from Slipman CW, Plastaras C, Patel R, Isaac Z, Chow D, Garvan C, Pauza K, Furman M. Provocative cervical discography symptom mapping. Spine J 2005;5:381-388.)

Figure 13–10 Cervical discogram pain referral map. A, C2-C3 discogram pain referral map. B, C3-C4 discogram pain referral map. C, C4-C5 discogram pain referral map. D, C5-C6 discogram pain referral map. E, C6-C7 discogram pain referral map. F, C7-T1 discogram pain referral pain map.

(Modified from Slipman CW, Plastaras C, Patel R, Isaac Z, Chow D, Garvan C, Pauza K, Furman M. Provocative cervical discography symptom mapping. Spine J 2005;5:381-388.)

Figure 13–11 Various types of cervical degeneration.

Figure 13–12 Pain drawings from patients with symptomatic disc disruption at the L3-4, L4-5, and L5-S1 levels.

Postoperative follow-up

After discography, the patient should be advised as follows:

Some degree of discomfort during and after this procedure is expected.

“Stress-bearing” or “strenuous” activities should be limited for 24 hours because of expected postprocedure discomfort.

Taking the day after the procedure off from work is recommended, but the decision to return to work is at the patient’s discretion.

A prescription for postprocedure pain medication is available for patients who require it.

Drinking plenty of fluids is recommended to clear the dye from the body.

Caveats

Intervertebral discography should be performed only when the source of the spinal pain remains unknown after various imaging and electrodiagnostic studies and an interventional procedure such as intradiscal electrothermal therapy (IDET), nucleoplasty, or fusion is to be scheduled.

Because the intervertebral disc is the largest avascular organ in the body, it is essential that the risk of discitis be minimized.

CASE STUDY 13.1

Figures 13-13 and 13-14 illustrates examples of discography.

Figure 13–13 Lumbar discography for endoscopic lumbar discectomy. The needle was confirmed to be inserted into the L4-L5 intervertebral disc at anteroposterior view (A), and the injected contrast agent was run over the anterior and posterior anulus fibrosis at lateral view (B). The pain was concordant with previous pain over the L5 dermatome and with intervertebral foraminal herniation on magnetic resonance imaging. The pressure was elevated just before there was a leakage of the contrast agent. These film findings could be interpreted as left downward migration of herniated nucleus pulposus.

Figure 13–14 Anterolateral approach for cervical discogram. The needle is inserted from the right side under oblique fluoroscopic guidance to keep the discogram needle from puncturing the esophagus. Needle is inserted just posterolateral to the sternocleidomastoid muscle and is directed to the anterolateral border of the disc.