ASRA Pain Medicine Update

Fluoroscopic epidural access, whether for an epidural steroid injection or for spinal cord stimulator lead insertion, is one of the most common procedures in the field of pain medicine. Safety is of particular importance when performing procedures involving the cervical spine, and therefore accuracy with needle placement is critical. An American Society of Anesthesiologists closed claims analysis for cervical procedures performed from 2005–2008 found 20 reported cases of direct spinal cord injury during interlaminar cervical epidural access.^[1]

“The CLO view is a clear favorite both for ease of access and for precision, likely enhancing overall safety of fluoroscopic epidural access.”

The likely primary driver is ineffective use of fluoroscopy; however, even more likely is the limitation of fluoroscopy itself. Because the distance from the epidural space to the spinal cord is diminutive, the depth of the needle as it approaches the cervical epidural space must be continually monitored and a radiologic landmark must serve as a depth marker for the epidural space. The commonly used depth view for fluoroscopic epidural access, the lateral view of the spine, affords neither. The needle tip is often poorly visualized or may not be visualized at all, and the spinolaminar junction is an inadequate radiologic landmark for the depth of the epidural space because of great variability.^[2]

The contralateral oblique (CLO) view, on the other hand, affords both. The needle tip is always well visualized and the relationship of the posterior boundary of the epidural space to the ventral inter-laminar line (VILL) is very tight (Figure 1).^[2] Thus, the needle can be placed directly within 1–2 mm of the target and the epidural space can be immediately accessed. The needle trajectory can be clearly projected (Figure 1).^[2] These advantages make the CLO view a clear favorite both for ease of access and for precision, likely enhancing overall safety of fluoroscopic epidural access. Its advantages extend to the lumbar spine as well, with demonstrated superiority in visualization and precision.^[3]

Step-by-Step Cervical and Cervicothoracic Epidural Access

1. Position the patient prone with their neck slightly flexed and forehead on a pillow.
2. Identify the correct cervical vertebral level (not higher than C6–C7).
3. Open the interlaminar space (may require cephalad tilt of the fluoroscope).
4. Identify the laterality of pain symptoms.
5. Mark the insertion point on the correct side. Remain within the lateral margin of the spinous process to prevent inserting the needle too lateral. A needle insertion point below the laminar edge provides an additional safety margin and improved needle trajectory.
6. Infiltrate with local anesthetic, making sure that the skin does not translate.
7. Advance the needle until it engages in firm tissue. This may be a few centimeters, depending on the patient.
8. Rotate the C-arm to 50 degrees CLO. The image intensifier obliquity is opposite to the side where the needle is inserted. For midline needle approaches, either direction may be used.
9. Confirm correct needle trajectory, identify the ventral laminar margin and conceptualized ventral interlaminar line, and estimate the distance to the VILL (Figure 1).
10. Advance the needle to just before the VILL in anteroposterior (AP) and CLO views.
11. Expect to lose resistance at or within 2 mm of the VILL (Figure 1). Do not advance more than 2.5 mm beyond the VILL. Loss of resistance can be subtle or nonexistent, especially with thin gauge needles.

Figure 1: Epidural space in the contralateral oblique view. 1A: As soon as the needle crosses the lamina and ligamentum, epidural access is attained. It is important that the angle of obliquity and the laminar angle are matched, mean laminar angle at C7–T1 has been shown to be 53 degrees, and 50 degrees may be used with loss of resistance expected on or just beyond the ventral interlaminar line (VILL). 1B: The VILL is a hypothetical line joining the ventral laminar margin in the contralateral oblique view. 1C: The loss occurs just on the VILL or slightly beyond (1–3 mm) but in the posterior half of the foramen. 1D: In the lateral view, the needle and the landmarks are poorly visualized.

Figure 2: Contralateral oblique view contrast spread patterns. 2A: Contralateral vacuolation is observed in this typical spread. 2B: A thick pattern may represent midline pooling or epidural space distension with restricted spread. Intradural spread may also appear like this. 2C: In the lumbar spine ligamentum flavum (outlined), hypertrophy has a typical appearance. The needle is advanced beyond the ventral interlaminar line before resistance is lost. 2D: Lower-intensity contralateral spread appears as only a thin film in the X-ray path.

Contract Patterns

A multitude of epidural contrast spread patterns may be seen in the contralateral view (eg, thick, thin, nerve root spread, multi-intense, vacuolations) depending on location of spread (eg, ipsilateral, contralateral, bilateral), and epidural distention may also occur (Figure 2).^[4] Physicians should familiarize themselves with those patterns yet recognize that despite the pattern, the dorsal margin of the contrast approaches the ventral margin of the lamina in the CLO view and subarachnoid or other spread must be considered when it is not observed.

Differences Between Cervical and Lumbar Access

The CLO view is equally efficacious in the lumbar epidural space because of its precision and superior needle visibility and trajectory; however, there are a few important differences.^[3]

A 45-degree angle of insertion is optimal for accessing the lumbar epidural space.^[3] The needle tip may advance several millimeters beyond the VILL in patients with ligamentum flavum hypertrophy (Figure 1). This is important to keep in mind during percutaneous, minimally invasive lumbar decompression procedures.

In patients with ligamentum flavum hypertrophy, laterally placed needles may be deeper to the VILL because the ligamentum is hypertrophied paramedially. This phenomenon is not observed with attempted cervical epidural access because the ligament is not generally hypertrophied to such a degree. In contrast, needles inserted in the midline in the cervical region may be slightly deeper to the VILL, which may be secondary to the needle having crossed the midline and flattening the laminar angle.

PRACTICE PEARLS

1. Ensure the rotation of fluoroscope is contralateral and at the correct angle.
2. Ensure the needle tip has not crossed the midline toward the obliquity of the C-arm.
3. Stop just before the VILL and carefully assess for loss of resistance.
4. If the C-arm does not oblique to 50 degrees to assess the right side, flip over the C-arm image intensifier or position the patient on the opposite side of table. Otherwise, use an angle of lesser obliquity such that the fluoroscope does not line up with the angle of the lamina, but recognize that this will reduce the CLO approach’s accuracy. This method requires special precaution because the epidural needle will appear further anterior with lesser obliquity.^[1]
5. If no loss of resistance is encountered immediately beyond the VILL, check needle for occlusion, make sure the needle tip is contralateral, inject a small amount of contrast (0.1 mL) to assess for posterior or epidural spread patterns, and check the lateral view for secondary confirmation.
6. On occasion, a needle inserted in the midline may advance 1–3 mm beyond the VILL in the cervical spine because of crossing the midline or laminar angle flattening. In contrast, a paramedial needle may appear deeper in the lumbar spine because of ligamentum flavum hypertrophy.

Limitations

Despite significant clinical advantages, physicians require substantial time to become familiar with the view before they can regularly adopt it. However, initially starting with the lateral view and using the CLO view as a secondary and confirmatory view will help them become more confident. Additionally, the view does not allow physicians to clearly discern between contralateral and ventral catheter placement, as might be required for spinal cord stimulator lead placement. To unequivocally distinguish between dorsal or ventral placement of a catheter, lateral view is needed. The view is also of limited use when the C-arm cannot provide the appropriate obliquity requisite.

Widespread Adoption

The CLO view is precise and easy to use. By providing improved needle visibility and clear radiologic landmarks for depth assessment, it may also enhance the safety of cervical epidural access. In addition to our studies, the CLO view has been favorably evaluated in larger numbers,^[5] but current reports do not indicate how well the approach has been adopted into clinical practice. National clinical practice surveys may aid in estimating technique integration.

One of the barriers to adoption of the CLO view may be a lack of familiarity with the radiographic anatomy. To address that concern, using the CLO view in combination with the lateral view helps physicians to rapidly improve their comfort and familiarity. In our experience, the learning curve is very steep, but once physicians are familiar with the CLO view, it becomes indispensable for interlaminar access and is the standard view at our academic medical center practice. Educational seminars, fellowship forums, workshops, and teaching rounds may further aid in the adoption and utility of the CLO view.

References

1. Rathmell JP, Michna E, Fitzgibbon DR, et al. Injury and liability associated with cervical procedures for chronic pain. Anesthesiology. 2011;114(4):918–926. https://doi.org/10.1097/ALN.0b013e31820fc7f2
2. Gill JS, Aner M, Nagda JV, Keel JC, Simopoulos TT. Contralateral oblique view is superior to lateral view for interlaminar cervical and cervicothoracic epidural access. Pain Med. 2015;16(1):68–80. https://doi.org/10.1111/pme.12557
3. Gill JS, Nagda JV, Aner MM, Keel JC, Simopoulos TT. Contralateral oblique view is superior to the lateral view for lumbar epidural access. Pain Med. 2016;17(5):839–850. https://doi.org/10.1093/pm/pnv031
4. Gill J, Nagda J, Aner M, Simopoulos T. Cervical epidural contrast spread patterns in fluoroscopic antero-posterior, lateral, and contralateral oblique view: a three-dimensional analysis. Pain Med. 2017;18(6):1027–1039. https://doi.org/10.1093/pm/pnw235
5. Derby R, Melnik I, Choi J, Lee SH, Lee JE. Reliability and safety of contra-lateral oblique view for interlaminar epidural needle placement. Pain Physician. 2017;20(1):E65–E73.