March 2012, VOLUME 198
NUMBER 3

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March 2012, Volume 198, Number 3

Neuroradiology/Head and Neck Imaging

Technical Innovation

Technique for CT Fluoroscopy–Guided Cervical Interlaminar Steroid Injections

+ Affiliation:
1 Both authors: Department of Radiology, Duke University Medical Center, Box 3808, Durham, NC 27710.

Citation: American Journal of Roentgenology. 2012;198: 675-677. 10.2214/AJR.11.6809

ABSTRACT
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OBJECTIVE. We describe the use of CT fluoroscopy as a guidance tool for performing interlaminar epidural steroid injections in the cervical spine.

CONCLUSION. CT fluoroscopy is an alternative method to perform cervical interlaminar steroid injections that allows precise needle placement in the epidural space.

Keywords: cervical, CT fluoroscopy, epidural, steroid injection

Cervicalgia has been treated with both surgical and nonsurgical techniques, the latter of which include epidural steroid injections. Steroid injections can be performed via an interlaminar approach, whereby the injection needle is placed between the lamina of the vertebral bodies into the epidural space dorsal to the thecal sac, or by a transforaminal approach, in which the needle is placed into the neural foramen adjacent to the exiting nerve root. Such injections have been performed using conventional fluoroscopy or conventional CT guidance or without imaging using only bony landmarks. The advent of CT fluoroscopy has provided an additional tool that allows precise needle localization utilizing cross-sectional imaging. Using low tube current and a spot-check technique, this technology provides acceptably low radiation dose to both patient and operator, with real-time visualization of needle placement, and has allowed us to perform injections at all levels in the cervical spine. To our knowledge, this technique for CT fluoroscopic–guided cervical interlaminar injections has not been described in detail previously.

Technique
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The patient is positioned prone on the table of the CT scanner (LightSpeed 16, GE Healthcare), which is equipped with tableside CT fluoroscopic hand controls and a foot pedal (Fig. 1). Pillows are placed under the upper chest to elevate the shoulders and allow the neck to fall forward in mild flexion. Scout images of the neck are obtained, and axial images limited to the level to be injected are obtained (axial technique: 120 kVp, smart tube current with a minimum of 100 mA and a maximum of 440 mA, and 2.5-mm contiguous slice thickness). A posterior oblique approach is planned from the axial images, and the proposed entry site is marked on the patient’s skin.

Using sterile technique, cutaneous anesthesia is administered using 2% lidocaine. A 22-gauge Quincke point spinal needle is advanced a short distance through the skin, taking care to advance only far enough to allow it to stand upright, but not deep enough to approach the spinal canal. The needle trajectory and position are confirmed with a CT fluoroscopic spot-check image. The tube current selected for the CT fluoroscopic images will depend on patient habitus, level injected, user preference, and other factors. In general, however, values in the 20–70 mA range provide adequate visualization. The needle is advanced in short increments, with repeated spot images, to the posterior margin of the ligamentum flavum, which is visible on fluoroscopic images (Fig. 2A).

A syringe is filled with contrast agent (iopamidol; Isovue-M 200, Bracco Diagnostics) diluted 1:1 with preservative-free sterile saline. The stylet is removed from the needle, and a 5-inch microbore extension tube (LifeShield, Hospira) is used to connect the contrast syringe to the needle hub. Use of the tubing reduces the likelihood of accidental needle movement during subsequent syringe exchanges. The microbore tubing that we use has a press-fit connector with a locking spin collar and holds a volume of 0.3 mL. Extreme care must be taken not to unintentionally advance the needle during attachment.

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Fig. 1 Asymptomatic volunteer. Photograph shows patient positioning for cervical interlaminar injection. Marker is placed on midline of neck to facilitate planning of approach. Table is equipped with hand controls (right) and foot pedal (bottom), which facilitate CT fluoroscopic spot checks.

A small amount (∼ 0.2 mL) of diluted contrast agent is injected to evaluate the position of the needle tip. If the needle tip is dorsal to the ligamentum flavum, contrast agent will spread along the posterior aspect of the ligament (Fig. 2B). In this case, the needle can be advanced with very slight incremental advances, followed by test injections of contrast agent and CT fluoroscopic spot checks. Because of the thinness of the ligamentum flavum in the cervical spine, the loss-of-resistance technique used for epidural injections in the lumbar spine may prove unreliable; needle placement must be judged visually.

Once in the epidural space, the anterior margin of the ligament will be outlined by contrast agent, and contrast agent will spread along the epidural space (Fig. 2C). Contrast agent should not be seen in the dependent (ventral) portion of the spinal canal, because this would indicate intrathecal placement of the needle tip. If intrathecal contrast agent is seen, the procedure may be stopped and rescheduled. Intravascular placement of the needle tip (likely within an epidural vein) should be suspected if contrast agent can be injected without resistance but no contrast agent is seen on the immediate fluoroscopic spot image. This would suggest washout of contrast agent by flowing blood. After contrast agent is confirmed within the epidural space, a second fluoroscopic spot image is obtained to evaluate for delayed washout of contrast agent that could be seen in a slower-flowing vein. We also routinely aspirate before injection to evaluate for intravascular placement; however, negative aspiration alone does not guarantee extravascular needle placement [1].

Once epidural positioning is confirmed, the contrast syringe is disconnected and replaced with a syringe containing steroid preparation. We use 2 mL of Celestone Soluspan (6 mg/mL, Schering-Plough), although other steroid preparations have been used for interlaminar steroid injections [2]. The steroid is injected into the epidural space, and the microbore tubing is flushed with 0.3 mL of contrast agent to ensure that no steroid is left in the dead space of the tubing. Intermittent spot checks with CT fluoroscopy are performed to ensure the absence of mass effect from the injectate. Such mass effect can uncommonly result from uneven spread of injected fluid in the epidural space and could necessitate discontinuing the injection. Once injection is complete, the needle is removed and the patient is observed for approximately 10–20 minutes before discharge.

Discussion
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Cervical interlaminar steroid injections have been traditionally performed using conventional fluoroscopy or without imaging guidance [24]. The advent of CT fluoroscopy provided a new guidance tool for interventional procedures, which has been implemented to perform lumbar spine injections, as well as transforaminal cervical injections [5, 6]. We have adapted these techniques to successfully perform cervical interlaminar injections. The principal advantage of this technique over conventional fluoroscopy is better visualization of the needle tip in relation to the ligamentum flavum, ensuring the correct depth of needle insertion.

Some authors have advocated limiting cervical interlaminar injection performed with conventional fluoroscopic guidance to the C6–7 level and below [79]. Although some proceduralists do perform injections under conventional fluoroscopy at higher cervical levels, there are anatomic considerations that may make these higher injections more challenging. The epidural space at higher cervical levels is only a thin potential space, with the ligamentum flavum and dural surface closely apposed [10]. Additionally, the ligamentum flavum may be incomplete in the midline, and in some patients, the interspinous ligament may be congenitally absent [10, 11]. For these reasons, the traditional loss-of-resistance technique may not be reliable in preventing penetration of the thecal sac or spinal cord itself. Although caution must be used above the C6–7 level, the ability to directly visualize the ligamentum flavum and spinal cord with CT fluoroscopy has allowed us to inject as high as C2–3 without complication.

Although the use of a noncutting tip needle has theoretic advantages in reducing the likelihood of inadvertent thecal sac puncture, our experience is that a Quincke needle allows finer control of small needle advancements. Specifically, a cutting tip needle helps to prevent the sudden unintended “pop-through” advancements that may occur as a result of the greater force required to advance a blunt-tipped needle through the ligamentum flavum. This finer control is of particular importance in the cervical spine because of the relatively thin epidural space compared with the thoracic and lumbar spine, although the use of a cutting-tip needle must be accompanied by careful vigilance for signs of unintended thecal sac penetration.

We often use diluted contrast agent during CT-guided procedures where contrast agent is necessary. In our experience, the use of undiluted contrast agent obscures visualization of the needle tip through the contrast pool, making subsequent manipulations more difficult. Conversely, overdilution of the contrast unacceptably limits visualization of the epidural space. Dilution of the contrast with preservative-free sterile saline to a final iodine concentration of approximately 100 mg/mL offers a good balance between these competing factors, in our opinion.

The use of local anesthetic with cervical interlaminar injections is controversial. Some proceduralists do not routinely mix local anesthetic with the injected steroid because of the theoretic risk of high cervical anesthesia that could accompany inadvertent thecal sac puncture [7, 12]. However, there is little information on the actual incidence of this type of complication. The use of contrast agent to confirm epidural location in our technique should serve to reduce this risk, and some experienced proceduralists may choose to use local anesthetic for diagnostic purposes or pain relief.

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Fig. 2A31-year-old man with bilateral neck and shoulder pain. A, CT fluoroscopic image before injection of contrast agent shows needle tip adjacent to ligamentum flavum (arrowhead) at C5–6 level.
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Fig. 2B31-year-old man with bilateral neck and shoulder pain. B, Image obtained after injection of contrast agent shows contrast spread posterior (dorsal) to ligamentum flavum, confirming that needle tip is outside epidural space.
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Fig. 2C31-year-old man with bilateral neck and shoulder pain. C,Image obtained after slight advancement of needle and reinjection of contrast agent shows contrast agent’s spread in epidural space anterior (ventral) to ligamentum flavum (arrow), which is outlined by two contrast agent injections.

Complications of interlaminar epidural steroid injections are fortunately rare and typically minor and can occur with both blind and imaging-guided techniques [8]. Minor complications using conventional techniques have included worsening neck pain, headaches, and flushing. More severe complications include inadvertent penetration of the dura, resulting in spinal anesthesia, epidural or subdural hematoma, meningitis, and direct puncture of the spinal cord [2]. Because direct visualization of the needle tip is possible with CT fluoroscopy, there should be minimal risk of direct cord penetration or unrecognized intrathecal injection using the CT fluoroscopic technique.

The decision of whether to use the transforaminal or interlaminar approach for cervical injections is controversial [2]. Although catastrophic complications have been reported with both techniques, the interlaminar approach has theoretic advantages in avoiding vertebral artery or radiculomedullary artery injury [1315]. In our experience, the best results have involved the use of a transforaminal approach in the setting of a clearly defined single-level radiculopathy; the interlaminar approach is preferred in the setting of bilateral symptoms, central disk pathology, and severe neuroforaminal stenosis that would preclude transforaminal spread of injectate.

In conclusion, CT fluoroscopy provides an alternative method to perform cervical interlaminar epidural steroid injections. This technique allows direct visualization of the needle tip relative to the ligamentum flavum and spinal cord, which may facilitate steroid injections in both the upper and lower cervical spine.

References
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Address correspondence to P. G. Kranz ().

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