Bruno Grignon

GuiHoz Department of Radiology, University Hospital of Nancy, Nancy, France

INTRODUCTION

Discography was first performed in 1948 by the Swedish radiologist K. Lindblom, who injected red lead contrast into cadaveric intervertebral discs (IVDs), to diagnose discal degenerative changes (1). At the beginning of the 21st century, discography is sometimes used as a diagnostic technique, mainly when computed tomography (CT), magnetic resonance (MR), or myelography is equivocal. It is followed, when possible, by CT examination (CT discography). Presently, however, discography is most often carried out as the first step of an operative procedure such as chemonucleolysis, intradiscal radiofrequency or laser therapy, or intradiscal injection of steroids or anesthetics.

ANATOMY OF THE INTERVERTEBRAL DISC

The IVD is interposed between the bodies of adjacent vertebrae and constitutes the main intervertebral joint (Fig. 1) (2-5). IVDs are cartilaginous synarthroses or symphyses, designed for weight bearing. The IVD is composed of two parts with more or less indistinct limits: a peripheral portion, the annulus fibrosus (AF), and a central space, the nucleus pulposus (NP). The AF is a ring structure, which is inserted by collagen fibers, also called Sharpey's fibers, into the adjacent vertebral bodies. It is dense and composed of concentric lamellae of fibrocartilage. The fibers that form each lamella run obliquely from one vertebra to another, and run at a right angle to those of adjacent lamellae (Fig. 2). This arrangement of fibers, at a right angle between two adjacent lamellae, explains the striation that is observed on discographic studies when the contrast medium is wrongly injected into the AF instead of the NP. The fibrous bundles are vertical in the periphery and oblique towards the center, providing a strong link between two adjacent vertebrae. However, it must be mentioned that at the lumbar level, the AF is thinner posteriorly than anteriorly and laterally.

The AF is made up of collagen fibers and fibroblasts and contains little water and proteo-glycans. The NP is the central core of the IVD, situated between the cartilagenous plates of the vertebrae and surrounded by the AF (Fig. 1). At the lumbar level, it is located more posteriorly than anteriorly. It is of gelatinous consistency, and contains a large amount of water (about 90% for a young nucleus), proteoglycans (which act on the water content, and are the target of chymopapain), and a few collagen fibers that are scattered randomly (Fig. 2). After the age of 20, the center of the NP is usually penetrated by collagen fibers, which has been described as the intranuclear cleft (6). Due to its high water content, the IVD acts both as a shock absorber against axial forces and as a fluid ball bearing during flexion, extension, and rotation. Unfortunately, the NP becomes progressively dehydrated with age and undergoes a gradual fibrous transformation. Tears may appear in the AF. The IVD is poorly supplied by blood vessels, which can be seen only in its periphery. The disc is partly maintained by the posterior and anterior longitudinal ligaments, which run, respectively, on the posterior and anterior aspects of the vertebral bodies, from the occipital bone to, respectively, the coccyx and the sacral bone. The posterior longitudinal ligament (PLL) is attached to the IVD and is often considered as contributing to the prevention of posterior herniation of the disc. However, this ligament is narrower and weaker than the anterior longitudinal ligament. In addition, the lower the lumbar vertebral level, the narrower the PLL. Posteriorly to the IVD, the vertebral canal contains the epidural space with the initial segment of the spinal nerves with their dural sheat crossing over at each level.

FIGURE 1 Anatomy of the disc. Line drawing showing the intervertebral disc in the sagittal plane. The annulus fibrosus (1) constitutes a fibrous peripheral ring, whereas the nucleus pulposus (2) is the central core of the disc and is the injection target in discography. Anterior longitudinal ligament (3). Posterior longitudinal ligament (4). Vertebral canal (5).

TERMINOLOGY OF DEGENERATIVE DISC DISORDERS

■ It must be kept in mind that, from one language to another, degenerative disc disorder terminology can be very confusing. Several words are commonly used to describe an identical degenerative discal feature, and the same terms may have a different meaning in another

■ It must be kept in mind that, from one language to another, degenerative disc disorder terminology can be very confusing. Several words are commonly used to describe an identical degenerative discal feature, and the same terms may have a different meaning in another

FIGURE 2 Microscopic anatomy of the disc. Annulus fibrosus (AF) (A, B). Scanning electron microscopy demonstrating the characteristic arrangement of the collagen fibers in the concentric lamellae, the disposition at a right angle of the fibers of two adjacent lamellae (A: x 8000), and the tight structure of the fibers in two adjacent lamellae (B: x 12,000). Nucleus pulposus (C). Scanning electron microscopy (x 12,000) showing the disposition of the collagen fibers that are scattered randomly, contrasting with those of the AF.

FIGURE 2 Microscopic anatomy of the disc. Annulus fibrosus (AF) (A, B). Scanning electron microscopy demonstrating the characteristic arrangement of the collagen fibers in the concentric lamellae, the disposition at a right angle of the fibers of two adjacent lamellae (A: x 8000), and the tight structure of the fibers in two adjacent lamellae (B: x 12,000). Nucleus pulposus (C). Scanning electron microscopy (x 12,000) showing the disposition of the collagen fibers that are scattered randomly, contrasting with those of the AF.

language, or even in the everyday use of the same language (7-13). Despite some attempts, no official standardization has been obtained (12,13).

■ The term "disc degeneration" is a general term, which means that the water content of the disc is decreased or lost. Consequently, the disc height is reduced, and there is a diffuse, circumferential, symmetric, annular bulge. Disc signal intensity is reduced on T2-weighted MR images. Degenerated discs often have tears or fissures in the AF, which may be seen at discography (Fig. 3).

■ Milette proposed a morphologic nomenclature based on the assessment of the disc contour (13,14). The degree of the disc extension beyond the interspace or DEBIT may be described as follows. Four categories of disc contour can be seen: normal (no disc extension), bulging disc, protruded, and extruded disc. The term "bulge" refers to a circumferential and symmetric DEBIT. Asymmetric or focal DEBIT is designated by the term "protrusion." When the DEBIT is focal and obvious or when there is no more connection between the disc material and the parent disc, it is referred to as an "extrusion" (13,14). The distinction between disc protrusion and disc extrusion has been discussed. The term "herniation" has been proposed to designate both lesions (15). However, this distinction has a clinical relevance, because disc protrusion as well as bulging disc can be asymptomatic, whereas disc extrusions are uncommon in asymptomatic patients (13). Moreover, the term "herniation" initially referred to a focal extension of the NP coming out of a disc space, whereas the true term was "herniation of the NP." This is too restrictive a definition, because it has been shown that the herniated material may be nuclear, annular, or endplate fragments (13).

INDICATIONS OF DISCOGRAPHY

■ Discography can be useful as a diagnostic technique or as the first step of therapeutic procedures.

■ As a diagnostic technique, discography is mainly used as an imaging method, but it can also provide a volumetric, a manometric, and a pain provocation evaluation of the disc (16), which will be further detailed.

FIGURE 3 Discographies performed at the L3-L4, L4-L5, and L5-S1 discal levels of a cadaveric spine. At the L3-L4 level: mildly degenerated disc. The nucleus pulposus (NP) is of large size, with a light center and pseudopolyps and communicates with a posterior radial tear and a thinner anterior tear in the annulus fibrosus (AF). The posterior discal border is normal at this level (arrows). At the L4-L5 level: degenerated disc with a flattened NP, several annular tears, and a bulge easily seen on the posterior border (arrows). At the L5-S1 level: large posterior protrusion opacified from the NP by a radial tear in the AF, with caudal migration, and mild epidural extravasation of contrast agent.

■ However, because it is an invasive technique, it should be reserved for patients with symptoms severe enough to require invasive therapy or surgery and when noninvasive diagnostic techniques have failed to reach a diagnosis, in particular, in cases of nerve root pain with negative or equivocal MR images, CT, or myelogram, or when disc disease is shown at multiple levels (9,17).

■ An uncommon indication is cases of low back pain where surgery is discussed. Goal of discopathy in such cases is to prove the discal origin of the back pain (9,18).

■ Most often, discography is performed as the first step of an operative procedure such as chemonucleolysis, nucleotomy, intradiscal radiofrequency, or laser therapy, or sometimes an intradiscal injection of cortisone or anesthetic (9).

GENERAL RULES OF TECHNIQUE Preparation

It is crucial to first interview the patient and review the physician's request and all the patient's medical and imaging records. Location, type, and nature of the pain must be clearly studied, as well as the patient's present and past history, and, in particular, a history of prior surgery. A physical examination is required, and the patient's psychological state must also be taken into account. Conversely, the patient has to be informed about discography, including the details of the technique, the risks, and the complications of the procedure.

Premedication and Neuroleptic Analgesia

Recent coagulation tests must be checked. If there is an allergy, the patient should have an aller-gological assessment (19,20). Conscious sedation is routinely used during discography to allow a comfortable procedure for the patient with the opportunity to reproduce the patient's pain.

Specific Case of the Discography Carried Out as the First Step of Chemonucleolysis

In such cases, attention must be paid to the possibility of a recent myelography. Because it has been shown that intrathecal injection of chymopapain may induce fatal hemorrhaging in rabbits and dogs (21), a minimum delay of 24 hours (21) or even seven days (22,23) is required between myelogram and chemonucleosis in order to allow the dural leak to seal. In addition, specific allergology tests should be performed.

Prediscography Computed Tomography

A prediscography CT in a prone position is not routine. However, it can be helpful to determine the location of the colon in this position, and to look for abnormalities of organs and vessels in order to choose the best path for the needle (8).

Plain Radiographs

Anteroposterior (AP) and lateral plain radiographs as well as "coned down" sagittal and AP views centered on the selected IVD level must be available before the discography. At the L5-S1 level, it is necessary to have a plain radiograph of the pelvis in order to study the position of the L5-S1 disc with regard to the transverse processes of L5 and the sacral bone.

X-Ray Room

Discography is carried out in the X-ray room under aseptic operating room conditions, including sterile drapes, gloves, and surgical gowns. Because both AP and lateral views of the disc must be available during the procedure in order to control the needle position, a portable C-arm image intensifier unit is the best device to carry out a discography. However, if such equipment is not available, it is also possible to use a single plane fluoroscopy table and an auxiliary X-ray tube, or even to rotate the patient to obtain biplane fluoroscopic control.

The Standard Discography Tray

It should include the following:

■ For local anesthesia: 10 mL syringe, 1% or 2% lidocaine (Xylocai'ne®), a 25-gauge (G) needle for the superficial planes, and, according to some authors, a spinal 9-cm 22-G needle for the deep planes (18).

■ Needles for the discography include a 15-cm 22-G and a 9-cm 18-G needle (L4-L5 level and upper levels) or a 20-cm 22-G and a 15-cm 18-G (L5-S1 level and corpulent patients).

■ A 2, 2.5, or 3 mL syringe for the contrast agent, a nonionic intrathecally well-tolerated contrast media, and sterile water.

■ Semiradiopaque ruler and indelible ink marker.

Patient Monitoring

An electrocardiogram monitor and a pulse oximeter allow monitoring of the patient.

Four approaches are theoretically possible to reach the disc space: the posterior, posterolateral (Erlacher), lateral extradural, and true lateral approaches (Fig. 4). Posterior and posterolateral approaches are usually contraindicated because nervous structures are on the needle path (24,25). With a true lateral approach, the colon may be punctured before the disc, with the risk of discal infection (22).

Therefore, a lateral extradural approach must be used (22,25-27), which is termed lateral as opposed to the posterolateral intradural of Erlacher (22,25). Using this approach, the site of insertion of the needle in the skin is 8 to 12 cm from the midline of the spine, with an angulation of 40° to 60° to the sagittal plane. The angle and direction of the needle depend on the IVD level and patient's morphology (Fig. 5). Because there is no relation between the side of approach and the side of the pain, theoretically either a right- or left-side approach may be used. However, for the lumbar spine, some authors recommend injecting on the right side because of the risk of wounding the artery of Adamkiewickz, which is four times more frequently located on the left than on the right (9).

Position of Patient

Discography may be performed with the patient in a strict lateral position, a prone position, or an oblique prone position. Each technique has both advantages and disadvantages, which will be further detailed.

Approach

FIGURE 4 Line drawing in the axial plane showing the various approaches of the nucleus pulposus. The "lateral" extradural approach alone is to be used. Source: From Ref. 16.

FIGURE 5 Line drawing showing the influence of the patient's build on the distance of the needle insertion point from the midline and on the angulation of the needle. Source: From Ref. 16.

TECHNIQUE OF LUMBAR DISCOGRAPHY Lumbar Discography with Lateral Positioning

The main advantage of the lateral position is a good view of bony obstacles, which allows an easy approach to the disc space, with a direction parallel to the vertebral end plates, and a rapid control of the placement of the needles. However, this position requires a clear three-dimensional view of the anatomy, and an exact lateral positioning of the patient (22).

Patient Positioning

The patient is placed in a lateral decubitus position, on his left side, on the radiolucent table. The hips and knees are flexed at 60° to 90° to reduce lumbar lordosis. The knees, ankles, and the left arm are protected by foam cushions. A radiolucent block or a folded sheet is placed beneath the flank to compensate for the thoracolumbar curve due to lateral decubitus (Fig. 6). The head is elevated. Perfect lateral positioning of the patient is essential. This position must be checked by fluoroscopy. It is crucial to have a strictly orthogonal orientation of the radiographic tube to the X-ray table (22).

Needle Insertion Point

This point lies about 7 to 11 cm lateral to the midline of the spine, just above the iliac crest, found by palpation. The distance between the midline and the needle insertion point is theoretically 7 cm at the upper lumbar spine and 11 cm at the lower lumbar spine, but depends in fact on the patient's build (Fig. 5). A semiradiopaque ruler is used to simulate the path of the needle on the fluoroscopic screen to determine the craniocaudal angle of the needle and the level of its site of

FIGURE 6 Lumbar discography with lateral positioning of the patient. The patient is placed on their left side. During the first part of the procedure, the X-ray beam must be strictly vertical and perpendicular to the table. Source: From Ref. 16.

FIGURE 7 Lumbar discography with lateral positioning of the patient. Lateral plain radiograph showing the radiopaque semiruler placed on the side of the patient and tilted as desired to choose the craniocaudal angle of the needle.

insertion (Fig. 7). This ruler is placed on the side of the patient and it is tilted as desired so that it projects between the needle insertion point and the posterior margin of the disc. The transverse processes must not be in the path of the needle, which runs as parallel as possible to the vertebral end plates. This angle is then marked on the skin (22).

Disinfection

The skin is prepared. A sterile surgical field is placed. Local Anesthesia

The superficial planes the needle will go through are anesthetized with a 25-G needle and 3 to 5 mL of lidocaine. Deeper planes may be anesthetized with a spinal 9-cm 22-G needle (18).

Needle Approach

The needle is inserted at an angle of 40° to 60° to the sagittal plane (Fig. 5). Its advancement must be controlled on the fluoroscopic screen. The needle can be first advanced to the facet joint. After contact, the needle is withdrawn a little and then advanced in a more sagittal direction (Fig. 8). Bony obstacles may be encountered and identified with the image amplifier. At the level of the pedicles, bony impingement is most often due to the transverse process, and at the level of the lower half of the vertebral body, to the facet joint. It is crucial to keep a clear three-dimensional image of the lumbar region in one's mind (22). Problems may also arise from the displacement of the patients, who often rotate their pelvis away from the needle. It may be useful to check the truly lateral position of the patient with the image intensifier (22). As soon as the needle has passed the line joining the transverse processes, the X-ray beam can be tilted to demonstrate the disc interspace (Fig. 9). The needle is then advanced toward the disc.

FIGURE 8 Lumbar discography with lateral positioning of the patient. The course of the needle, which is first advanced to the facet joint, then withdrawn a few centimeters and more sagittally oriented. Source: From Ref. 16.

When the contact with the AF is felt, the tip of the needle should be exactly on the vertical line passing through the posterior borders of the vertebral bodies (Fig. 10) (22). If the tip of the needle is anterior to this line, the approach is too lateral and too sagittal, and the needle will pass anterolateral to the NP. The angle of the needle insertion must be changed to a more coronal direction. If the tip of the needle is posterior to the line, the approach is too medial and coronal (Fig. 10). Once the needle is correctly placed, the patient is rotated to an oblique position and the X-ray beam is tilted to the same angle as the needle in order to check the position of the needle tip, seen as a metallic dot, in relation to the disc width (22). The ideal needle position is at the junction between the medial and middle-third of the disc width (Fig. 11). In that position, the NP can be reached without bending the needle. The stylet of the 18-G needle can be removed, and a 22-G needle can be inserted into the 18-G needle. The thin needle is then advanced toward the center of the NP, where a sensation of sudden decreased resistance can be perceived. If the needle is lateral to this point, a mild bending of the 22-G needle is needed to reach the NP. During this phase of the procedure, proper needle placement at the mid-height of the IVD should also be obtained. An AP view is performed to check the correct position of the tip of the 22-G needle, which is ideally located on the midline and equidistant from the two vertebral end plates. On a lateral view, the tip of the thin needle is ideally located at the junction between the posterior and middle-third of the disc (Fig. 12). AP and lateral plain radiographs should be obtained before disc injection.

Lumbar Discography with Prone Oblique Positioning

The main advantage of this position is easy three-dimensional control of the needle position, because the puncture point projects as a simple dot on the fluoroscopic screen. It is also the

FIGURE 9 Lumbar discography with lateral positioning of the patient. The X-ray beam is tilted in order to profile the discal space exactly as soon as the needle has passed the line joining the transverse processes. Source: From Ref. 16.

FIGURE 10 Lumbar discography with lateral positioning of the patient. Line drawing showing the placement of the 18-G needle on a lateral fluoroscopic view. In (A), the needle placement is too medial, and the angulation of the needle must be corrected in a more sagittal direction. In (B), the placement is proper: the tip of the needle projects on the line of the posterior border of the vertebral bodies. In (C), the needle placement is too I ateral; the needle must be inserted in a more coronal direction. Source: From Ref. 16.

FIGURE 11 Lumbar discography with lateral positioning of the patient. Line drawing showing the right position for the needle when the patient is placed in an oblique position. The tip of the needle must appear at the junction between the internal and middle-third of the width and at midheight of the disc.

easiest technique of approach especially for the less-experienced physician. However, with this technique, it is somewhat more difficult to approach disc space in a direction parallel to the vertebral end plates (18,22).

Patient Positioning

The patient is placed in an oblique prone position. The patient's right side is up, and a radio-lucent block is put under his left side. The right hip and knee are flexed. A small cushion is placed under the right knee for his comfort. The X-ray beam is tilted to profile the disc space (Fig. 13). The patient is then rotated to obtain a "triangle of puncture" delineated at the L4-L5 level, by the right superior facet of L5, the lower end plate of L4, and the iliac crest (Fig. 14). Disinfection and local anesthesia are then performed as previously described.

Needle Approach

The 18-G needle is inserted following the angle of inclination of the X-ray tube, so that its distal tip projects in the center of the triangle of puncture. The advancement of the needle is

FIGURE 12 Lateral (A) and anteroposterior (B) plain focussed radiographs showing the proper placement of the needles. The tip of the 22-G needle is projected at the union of the posterior third and middle third of the disc on the lateral view and on the spine midline.

FIGURE 13 Lumbar discography in prone oblique position at the L4-L5 level. Positioning of the patient. The X-ray beam is tilted to profile the disc space in order to obtain the triangle of puncture. Source: From Ref. 16.

FIGURE 14 Lumbar discography in prone oblique position at the L4-L5 level. Line drawing demonstrating the "triangle of puncture," as seen on oblique roentgenogram. The triangle is bordered by the inferior end plate of the L4 vertebra, the superior facet joint of L5 posteriorly, and the iliac crest anteriorly.

FIGURE 15 Lumbar discography in prone position. Line drawing showing the positioning of the patient, placed prone on the fluoroscopic table with a cushion under the abdomen. The spine midline, an 8 cm para-median lateral line to the midline, and the desired discal level are marked on the skin with indelible marker.

then controlled fluoroscopically. When the needle has reached the AF, its stylet is removed, and the 22-G needle is inserted into it. The patient is then placed at a strict lateral position, and the X-ray beam is tilted in order to profile the disc space. The 22-G needle is then carefully advanced until its distal tip reaches the junction between the posterior-third and the middle-third. The position of this needle should also be checked on an AP projection. It must be projected in the center of the IVD. If this is not the case, the needle must be repositioned.

Lumbar Discography with Prone Positioning

The greatest advantage of the prone position is that it is the most stable and provides the best immobility of the patient (9). It is also easier for the physician to orient the needle toward the disc space (9). However, this approach is particularly difficult for the L5-S1 level.

Patient Positioning

The patient is placed in a prone position. A cushion is put under his abdomen in order to reduce his lumbar lordosis (Fig. 15). The patient's knees and feet are placed on a small cushion. The knees are semiflexed.

Skin Markers

A vertical paramedian line at 8 cm (9-10 cm in obese patients) from the midline of the back of the patient and the desired disc level defined with fluoroscopy are marked on the skin. At the L3-L4 and L4-L5 intervertebral levels, the site of skin puncture is at the intersection between these two lines. For the L5-S1 level, the needle has to be inserted higher, roughly midway between L3-L4 and L4-L5 (9).

Needle Approach

For the L3-L4 and L4-L5 levels, the needle is approached at an angle of 30° to 60° to the sagittal plane. Needle advancement is controlled on the X-ray intensifier screen. At the L5-S1 level, an additional caudal angle must be given. Moreover, at this level, it is almost always necessary to bend the tip of the 22-G needle to reach the disc center.

Discography at the L5-S1 Level Anatomical Specificities

This approach of the disc space is more difficult at the L5-S1 level because of the presence of the iliac crest (Fig. 16), a reduced intersomatic space, the caudal orientation of the disc plane at this

FIGURE 15 Lumbar discography in prone position. Line drawing showing the positioning of the patient, placed prone on the fluoroscopic table with a cushion under the abdomen. The spine midline, an 8 cm para-median lateral line to the midline, and the desired discal level are marked on the skin with indelible marker.

FIGURE 16 Puncture at the L5-S1 level. Line drawing showing the pathway of the needle in the frontal plane with regard to the iliac crest. The more lateral the site of insertion of the needle, the higher it will be, and the more obliquely downward the pathway of the needle will be. Source: From Ref. 16.

FIGURE 16 Puncture at the L5-S1 level. Line drawing showing the pathway of the needle in the frontal plane with regard to the iliac crest. The more lateral the site of insertion of the needle, the higher it will be, and the more obliquely downward the pathway of the needle will be. Source: From Ref. 16.

level (9), and an increased width of the neural arch (22). The space between the transverse process of L5 and the sacral bone is often narrow especially when the L5-S1 disc is deeply embedded. The build of the patient may make the procedure even more difficult.

Patient Positioning

Lateral positioning of the patient is recommended for this level, particularly when the L5-S1 disc is deep relative to the pelvis, because the radiolucent block placed under the flank of the patient is more efficient in this position than in the prone oblique position. The latter position and the prone position are sometimes possible when the iliac crest is not overly high, with the knowledge that the needle approach cannot be strictly parallel to the vertebral end plates (18,22).

Needle Insertion Point

The side with the maximum distance between the sacral wing and the L5 transverse process on the plane radiograph is selected for skin puncture (22). The patient is positioned lateral on the opposite side. It is important to place a radiolucent block beneath his flank in order to open both the IVD and the space between the sacral wing and the transverse process, as well as to lower the iliac crest. A marker is placed at 8-cm to 10-cm lateral to the midline, which indicates the point of puncture. As described for the L4-L5 level, a ruler simulating the path of the needle is tilted as required in order to project between the puncture point and the posterior border of the L5-S1 disc. The approach must be as parallel as possible to the disc space. A line representing this approach is marked on the patient's skin.

Needle Approach

The 15-cm 18-G needle is inserted at an angle of 40° to 60° to the sagittal plane as at the L4-L5 level, but with an additional caudal orientation. However, because the neural arch is wider at the L5-S1 level than at the level above, it is often necessary to bend the 22-G needle in order to reach the center of the disc. The distal part of the needle must be carefully curved in such a manner that its bevel is placed on the convex aspect of the curve. The required degree of curvature can be estimated on the oblique view, as illustrated by Figure 17. The curved 22-G is then advanced in the 18-G needle and then rotated, so that its concavity is medial and cephalad (22).

DISCOGRAPHY Needle Placement

■ The contrast agent is injected once the proper needle placement has been checked on both AP and lateral views (Fig. 18). The contrast media must flow away from the tip of the needle and cross the discal midline as soon as the injection begins (Fig. 19).

Annulograms

In case of injection into the AF, the contrast media may appear to be in a correct location, central into the disc space on one radiographic view, and will be lateral and not central into the disc

FIGURE 17 Degree of curvature of the 22-G needle according to the position of the 18-G needle on an oblique view. Source: From Ref. 16.

FIGURE 18 Anteroposterior (A) and lateral (B) plain-focussed radiographs showing the proper placement of the needle at the L5-S1 level.

space on the orthogonal view (18,20). A striated appearance of the contrast media can also be observed, due to the arrangement of the AF fibers (Fig. 20).

Virtual Space

Quinnel and Stockdale have also showed that the contrast medium may be injected in a virtual space, between the NP and the inner AF. In such cases, the contrast media appears as a crescent, displacing the true nuclear cavity (28).

Vascular Opacification

In case of chemonucleolysis, absence of vascular opacification should be confirmed at fluoroscopy before chymopapain injection because this finding contraindicates enzyme injection (22,29-31).

FIGURE 19 Anteroposterior (AP) (A) and lateral (B) plain radiographs during the beginning of the injection of contrast agent at the L4-L5 level, using a single-needle technique. Dense opacification in the center of the disc on both AP and lateral views as well as the flowing away of contrast media from the tip of the needle, together ensure the right positioning of the needle.

FIGURE 19 Anteroposterior (AP) (A) and lateral (B) plain radiographs during the beginning of the injection of contrast agent at the L4-L5 level, using a single-needle technique. Dense opacification in the center of the disc on both AP and lateral views as well as the flowing away of contrast media from the tip of the needle, together ensure the right positioning of the needle.

FIGURE 20 Annulography. Anteroposterior (A) and lateral (B) plain radiographs show a rectangular opacification in the disc which remains anterior. A striation of the opacification can be seen.

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