Lumbar discography is an invasive diagnostic procedure that involves, instillation of iodinated contrast into the nucleus pulposus after inserting a needle under fluoroscopy. This procedure is done with an aim to get information on the morphology and integrity nucleus pulposus, vertebral endplates and annulus fibrosus.
In addition to this, the measured contrast injection allows determination of intradiscal pressures and response of the patient to this stimulation is a measure of pain caused by disc.
Thus lumbar discography not only to defines the anatomical architecture of the disc but also tells whether a particular disc is painful.
Basis Of Lumbar Discography
Changes in the intervertebral disc and annulus are potential sources of low-back pain.Pain causedd by internal disruption of the normal structural and biochemical integrity of the symptomatic disc is called discogenic pain. Discography is done to establish and confirm discogenic pain.
Lumbar discography provokes pain by the following mechanisms –
- Increase of intradiscal pressure may be caused by the injection of contrast material into the disk may increase
- Biochemical or neurochemical stimulation that causes pain
- An increase in intravertebral pressure.
Radiography, myelography, CT scanning, and MR imaging can demonstrate degenerative changes of the spine, however, none of these studies alone or in combination can specifically identify the disc as a pain generator.
It should be noted though that in most of the cases clinical examination and magnetic resonance imaging can identify the offending disc with sufficient certainty and discography is not routinely needed.
Lumbar discography is not indicated or necessary to confirm the unequivocal presence of herniated discs that coincide with findings on clinical examination.
Indications of Lumbar Discography
Lumbar discography should be performed only if adequate attempts have failed to reveal the etiology of the back pain.
Persistent, severe symptoms when other diagnostic tests have failed to clearly confirm a suspected disk as a source of the pain.
The primary indication for lumbar discography is chronic low back pain with or without radiating pain in the absence of MRI imaging-documented neural compression or when MRI is equivocal or when clinical findings point to one level or one side and myelography or MR imaging indicates a different level, or when the disc protrusion is asymmetrical to the contralateral side of the patient’s symptoms.
In some cases, far-lateral disc herniations may be confused with nerve sheath tumors or hematomas and discography can establish the diagnosis.
Lumbar fusion is a commonly performed surgery and cases which develop recurrent back pain are good candidates for discography because imaging studies are often too considerably distorted by artifacts of the instruments.
A positive discogram at the fused level may identify a persistently painful disc, suggesting the need for disc removal and interbody fusion.
Discography can define patients who are poor surgical candidates. Some patients exhibit intolerance to mild painful stimuli, even when narcotic agents are given under sedation. Patients in whom profound pain intolerance is demonstrated during discography are often very difficult to manage postoperatively and are more prone to developing chronic pain syndromes and failures.
Identification of Psychological Abnormalities
Discography can also be used to identify patients with psychological abnormalities or those for whom secondary gain issues may be at stake. Provocation of pain at levels that are morphologically normal on post-discography CT scanning and MR imaging is a contraindication for surgical intervention. Also, pain provoked at multiple levels in combination with equivocal morphological abnormalities often suggests the presence of secondary gain or psychological factors that are associated with poor surgical outcomes.
Recurrent Disc Herniations
Evaluation of abnormal disks or recurrent pain from a previously operated disk or lateral disk herniation is another indication for discography. Recurrent disc herniations, especially when associated with significant epidural and perineural scar tissue, can present as diagnostic dilemmas. Magnetic resonance imaging with and without contrast can identify recurrent disc herniations, but often the diagnosis remains in question. Discography is to clarify the significance of recurrent pain syndrome in patients after discectomy..
How Lumbar Discography Is Done?
Preparation of The Patient
Before the patient is prepared for the procedure, a discussion of the procedure should be done and associated risks like disc infection, superficial infection, bruising and swelling at the site of piercing and flare up of pain should be discussed.
Obtain a thorough history of the patient and ask for exact location of his/her pain. The patient should complete a pain diagram. The amount of back pain compared with buttock pain and leg pain should be noted. Allergy to contrast is noted and the need for prophylactic medications is addressed.
After obtaining an intravenous access and a fluid is started. The patient is given prophylactic antibiotics.
The patient is placed in the desired position. While slightly oblique and at a 45° angle to the bed and rotated forward is often optimum position, some may prefer to use lateral or prone position.
Patient’s blood pressure and pulse oximetry is monitored and the patient is sedated but enough to have a recollection of the discographic procedure.
The back is cleaned with betadine and prepared.
The fluoroscope is then positioned. Approaching the lumbosacral disc requires a cranial tilt of the C-arm at roughly 45°. The goal of tilting the C-arm is to obtain good visualization of the disc space.
At this point, a local anesthetic (1% lidocaine) is infiltrated to the skin and musculature. This needle is placed via a right paramedian approach. Anteroposterior and lateral images of the disc are obtained. The needle tip should be in the center of the disc space on both of these views.
Water-based iodine contrast is mixed with antibiotics for injection.
A pressure syringe is recommended which can also inform on the opening pressure, the pressure at the onset of pain, and maximum pressure. The correlation of opening pressure and pressure at pain onset is influences surgical technique. The integrity of the disc can be determined by assessing the amount of pressure it can hold. The pressure in an incompetent disc does not rise due to leakage contrast.
A typical nonpainful lumbar disc should be able to hold pressure up to at least 90 mm H2O.
The disc morphological characteristics, the presence of a complete or partial tear, and any epidural spread of contrast is noted.
The patient is questioned for location, intensity, and quality of pain produced by injection of the material and should quantify his pain on a scale of 0 to 10.
Plus the pain should be classified as strongly concordant, partially concordant, or disconcordant.
Videotaping during discography is of both of the disc injection phases and the patient’s facial expression can help the surgeon to determine the response.
Pain mannerisms are important to note. Exaggerated pain mannerisms may suggest poor surgery related outcome.
‘The information recorded during discography should tell following parameters-
- Resistance to the injection
- Amount of contrast material injected
- Volume at which the patient experienced pain
- Pattern of dye distribution (eg, diffusion, a location of fissure, extravasation, herniations, Schmorl nodule)
- Pressure at which patient experienced “pressure sensation”
- Pressure at which patient experienced “pain”
- Pain location, character, distribution, intensity, and concordance or discordance with the patient’s typical pain and pain pattern
- Pain intensity recorded on a 0-10 scale
Attention should be paid to note whether the pain is similar to or exactly like the symptoms for which the patient seeks relief. The location of the pain and its intensity should be noted.
Complications of Lumbar Discography
Complications associated with lumbar discography include
- Spinal headache
- Intrathecal hemorrhage
- Accidental intradural injection
- Damage to the disk
- Retroperitoneal hemorrhage
- Increased pain
In rare cases, discography has been found to result in disk herniations
Pain at low pressures is mostly due to chemical irritation. If low resistance is encountered, a tear through the annulus should be suspected. Pain at high pressures is generally due to mechanical irritation, end-plate deflection, or stimulation of pressure receptors.
If a large volume of contrast can be injected, the disc has degenerated or there is a fissure extending through the outer annular wall.
Dallas Classification of Lumbar Discography Results
The discogram is normal manometrically, volumetrically, and radiographically and produced no pain. Contrast located centrally in the axial and sagittal projections. After discography CT scan shows normal disc contour.
Identical to type 1 except that it is positive for the reproduction of pain.
Annular tears lead to a radial fissure. This group is subdivided further into types
- 3a Posterior radial fissure
- 3b fissure radiates posterolateral
- 3c Fissure extends lateral to a line drawn from the center of the disc tangential to the lateral border of the superior articulating process).
Radial fissure reaches the periphery of the annulus fibrosus, nuclear material may protrude, causing the outer annulus to bulge.
Nuclear material may extrude beneath the posterior longitudinal ligament and come in direct contact with either the dura or a nerve root.
Sequestrated disc. Manometrically, volumetrically, and radiographically, the discograms are always abnormal. Familiar pain may be reproduced only if enough pressure is generated against the free fragment to cause stimulation of the pain-sensitive structures.
The end stage of this degeneration is internal disk disruption, characterized by multiple annular tears. The discograms are abnormal manometrically and volumetrically, and familiar pain may or may not be reproduced.
The contrast usually fills the entire interspace in a chaotic fashion. The discogram/CT scan shows contrast extravasation throughout multiple annular tears.
Discography provides valuable information in the cases where it is indicated but it is not without controversy. The available literature, however, agrees that it can be used in selected patients.