Applied Radiology

Dr. Kapoor is a Resident, Dr. Rothfus and Dr. Grahovac are Staff/Attending Physicians in the Division of Neuroradiology, Department of Radiology, University of Pittsburgh Medical Center, Pittsburgh, PA.

A number of new spine procedures are being performed for treatment of pain of discogenic origin such as intradiscal electrothermy (IDET), vertebral fusion, and microdiscectomy. Most of these procedures require discography as a part of the preoperative work-up to identify the disc level that is the source of pain and to identify intrinsic disc pathology. Magnetic resonance imaging (MRI) is widely used in evaluating structural integrity of the intervertebral disc; however, MR imaging is not reliable in detecting internal disc pathology, especially in the cervical region. ¹ Often surgeons request discography preoperatively to accurately assess 1) the culprit disc responsible for pain; and 2) the probability of successful outcome of the operation. The surgical and nonsurgical treatment outcomes of discogenic pain are significantly improved by discography. ^2,3

Discography is technically challenging, and thorough knowledge of the spinal anatomy is a must for performing the procedure safely and accurately. Among other reasons, faulty technique not only increases patient discomfort, but may also confound examination reliability by leading to false-positive results. ^4-6 Different techniques for performing discography have been described by various authors. ^7-11 These techniques vary with the patients in the sitting, prone, or lateral decubitus positions; using the paravertebral approach or transdural approach; and using 22-gauge straight needles, 21-gauge and 26-gauge co-axial needles, needles with single end-holes, and multiholed needles. We describe a simplified technique for cervical, thoracic, and lumbar discography using bony landmarks identified easily on fluoroscopy.

Technical requirements

All discography is performed on ambulatory outpatients using C-arm fluoroscopy, strict aseptic technique, minimal conscious sedation (intravenous [IV] fentanyl and midazolam) and local anesthesia (1% to 2% buffered lidocaine). Some authors advocate the use of intradiscal antibiotic (cefazolin) routinely for all discography to prevent discitis. ⁴ We only use intravenous antibiotics prior to cervical discography. During injection of contrast, the patient's response is recorded, ie, whether pain is concordant or discordant, as well as the level of pain intensity on a scale of 0 to 10 (10 being the worst). Subjective resistance to injection and/or adequate visual depiction of the intervertebral disc and/or response of the patients to the injection is used, singly or in combination, as the end point of the injection. Following discography, all patients undergo a CT scan of the injected discs. A normal disc should be injected prior to study of the suspect disc as a baseline or control to improve reliability of the examination.

Technique for cervical discography

The patient is placed in a supine position on the fluoroscopy table. After prepping the neck, intravenous medications for conscious sedation are administered. Skin and subcutaneous tissue at the anticipated site of needle entry (as seen with oblique fluoroscopy) are anesthesized with 1% buffered lidocaine. The X-ray beam is angled 30š to 45š lateromedially to the cervical spine. The beam is also angled craniocaudally so that it is tangential to the intervertebral disc being studied. The needle entry is usually in the right side of the neck. A "down-the-barrel" approach is used with a 25-gauge, 8.89-cm spinal needle.

On oblique fluoroscopy, the target is the "uncinate-triangle" formed by the uncinate process laterally; the superior end plate of the lower vertebra inferiorly; and an imaginary line joining the tip of the uncinate process and the superomedial tip of the vertebral body (Figure 1).

An antibiotic (cefazolin) is administered intravenously while the neck is being prepped. Following local anesthesia, the carotid vessels are gently retracted laterally with the left hand and, under intermittent C-arm fluoroscopy, a 25-gauge needle is guided toward the uncinate-triangle described above. The needle passes between the thyroid cartilage and trachea medially and the carotid vessels laterally (Figure 2) and enters the intervertebral disc at its anterolateral aspect (Figures 2 and 3).

By using this technique, we avoid the potential risk of complications by injury to the vertebral artery that is protected by the uncinate process (Figures 1 and 2). Figure 4 is an example of a positive cervical discography.

Technique for thoracic discography

Using oblique fluoroscopy, with the patient prone, the X-ray beam is angled 30š to 45š lateromedially to the thoracic spine. The beam is also angled craniocaudally so that it is tangential to the intervertebral disc being studied. A down-the-barrel approach is used with a 25-gauge, 8.89-cm spinal needle. On oblique fluoroscopy the target is a "box"--the vertical sides of this box are formed medially, by a line joining the pedicles and laterally by a line joining the head of the ribs (Figure 5). The horizontal margins of this box are the superior and inferior vertebral end plates (Figure 5). The path of the needle as seen on cross-sectional imaging is depicted in Figure 6.

Using aseptic technique, intermittent fluoroscopy is used to guide a 25-gauge needle toward the box described above (Figure 7). The needle passes between the superior articular facet medially and the head of the rib laterally (Figure 5) and enters the intervertebral disc at its posterolateral aspect. Figure 8 is an example of a positive thoracic discography.

Co-axial technique for lumbar discography

The procedure is performed with the patient in the prone position. The X-ray beam is angled 25š to 35š lateromedially to the spine to get the "Scotty-dog" appearance of the vertebra. The beam is also angled craniocaudally so that it is tangential to the inferior end plate of the intervertebral disc being evaluated. This view depicts the pedicle, superior articular facet, and lateral margin of the disc (Figures 9 and 10). The needle entry is opposite the side of usual back pain if the pain is predominant on one side.

A down-the-barrel approach is used with a co-axial needle combination (an outer 20-gauge, 8.89-cm and an inner, curved 25-gauge, 15- to 20-cm needle). On oblique fluoroscopy the target is the "safe-window" formed by the superior articular facet medially, the superior end plate of the lower vertebra inferiorly and an imaginary line joining the tip of the superior articular facet and the superolateral tip of the vertebral body (Figure 10). Under intermittent, biplane fluoroscopy, the 20-gauge outer needle is guided into the back (Figure 11) so that its tip comes to lie at the level of, or just anterior to, the superior articular facet as seen on lateral fluoroscopy.

The 25-gauge needle is then hand-curved to approximately 30š to 45š, and advanced through the 20-gauge needle under intermittent fluoroscopy into the posterior third of the intervertebral disc (Figures 11 and 12). The entry point of needle into the lumbar disc is at its posterolateral margin.

By using this technique, the needle will enter the disc posterior to the nerve root exiting from the lumbar neural foramen (Figure 9). In the lumbar region, a normal or "control" disc is injected (Figure 13) prior to study of the suspect disc as a baseline of the patient's pain.

Conclusion

In our experience, the safe windows described above in the cervical, thoracic, and lumbar spine are easily identifiable landmarks on oblique fluoroscopy and can be used reliably as a safe and simple approach to discography.

Acknowledgments

The authors would like to thank Eric Jablonowski and Mike Purvis for their help with the illustrations.