An Alternative to the Transforaminal Cervical Epidural: A Selective Dorsal Epidural

Dear Editor, Consideration of alternative approaches for cervical transforaminal epidural steroid injections (CTESI) is beneficial even in light of the improved safety profile provided by the use of nonparticulate steroids [1]. The risk for stroke caused by particulate steroid emboli is reduced by the use of nonparticulate steroids. Intravascular injection, another complication seen with CTESI, is usually venous [2] and therefore does not carry the same risks as arterial injections. However, there are other complications that arise from CTESI: vasospasm or vessel dissection resulting in cerebral edema and brainstem hemorrhage, spinal cord or nerve trauma resulting in neurologic deficits [3], and temporary quadriplegia resulting from accidental arterial injection of local anesthetic [4]. Cervical epidurals have a higher risk of accidental intravascular injection (19.4%) than epidurals at the lumbosacral level (10.8–11.2%) [5]. CTESIs are generally considered to be safer when the needle is positioned in the posterior aspect of the foramen as the vertebral artery is known to occupy the anterior foraminal space. However, cadaver dissections indicate that vertebral artery variations (lateral loops or accessory arteries) have a 20% prevalence and can be present in the posterolateral area of the neural foramen, posterior to the exiting nerve root, invading the traditional needle target zone for CTESI [6]. Computerized tomography (CT)–guided transforaminal approaches that maintain a posterior needle position have been published in Europe [7] and may reduce the risk of puncturing vertebral artery variants that extend posteriorly into the foramen. In response to a continuing need for side-specific epidurals, and in order to decrease the risk of nerve injury or accidental cannulation of the anteriorly located vertebral artery, we propose a selective dorsal technique performed with fluoroscopy. While this technique, like the traditional techniques, places contrast and medications in the posteroinferior foraminal space, it differs by keeping the needle tip extraforaminal. For the selective dorsal epidural (Figure 1), the patient is positioned prone, with the head turned to the contralateral side. The skin entry point is 1 cm medial and inferior to the waist of the articular pillar that corresponds to the targeted exiting nerve. The C-arm is angled in a cephalo-caudad angle to show the waist of the articular pillar at the appropriate level. An 18-gauge cm sharp-beveled needle is used to open a portal in the dermis and underlying tissues and then removed in order to introduce a 12.7 cm, 25-gauge, PENCAN pencil-point spinal needle (B. Braun Medical Inc., Bethlehem, PA, USA). The spinal needle has the distal 5 mm bent (by the practitioner) at an approximate 30 degrees, and the side port directed medially. We prefer a pencil-point spinal needle due to its safety and due to the side port feature. The risk of inadvertent vascular injection with pencil-point needles is comparable with that of blunt-tip needles (16.6% vs 15.6%) according to an observational trial of lumbosacral transforaminal injections [8]. The larger gauge (25G) and the bent tip allow for more deflection in deeper tissues, which translates to greater ability to steer the spinal needle. The spinal needle is maneuvered, under intermittent fluoroscopic visualization, over bone, to the posterior OS of the articular pillar. The spinal needle is walked onto the waist of the articular pillar, as would be done for a posterior approach to a cervical medial branch block. At this point, the two procedures differ and we advance the needle anteriorly approximately 0.5 cm, with the tip coming to rest just at, or medial to, the waist of the articular pillar. An initial anteroposterior view and a lateral radiographic view are obtained to determine needle depth. Once the needle tip is advanced in the extraforaminal zone, we ascertain that the needle tip is not penetrating a vascular structure by injecting contrast under live fluoroscopic visualization (Figure 2). If there is any questionable flow pattern, digital subtraction angiography (DSA) is applied. Optimal spread of the contrast is medial to the tip of the needle, in an intraforaminal pattern and into the epidural space, although an extraforaminal spread has also been found to be effective [9]. The purpose of the test dose is to prove that the needle tip is nonvascular, in order to both diminish risk and increase efficacy. Finding a lack of vascular uptake, checking on both the anteroposterior and lateral visualization, we complete the procedure by injecting a mixture of 1 mL of preservative-free 1% lidocaine and 1 mL (10 mg) of dexamethasone. An illustration of the selective dorsal epidural approach at the cervical level. A) An anteroposterior view of a left midcervical selective dorsal epidural with flow of contrast into the foramen and the epidural space. B) Lateral radiographic view of a selective dorsal epidural. In our opinion, a selective dorsal approach employs easily identifiable vertebral landmarks and decreases the chance of advancing the needle tip into an anterior position. By maintaining the needle tip in the extraforaminal zone, the incidence of puncturing vessels at the foraminal opening is reduced [2]. The risk for nerve root trauma, spinal cord injury, or high spinals may also decrease. A number of concerns may arise when considering adoption of this technique. Does it sufficiently decrease liability and risks? Whether this approach decreases complications cannot be answered without a high-powered, prospective study. Based on anatomical studies, we think that an increased safety margin is provided by maintaining a dorsal, extraforaminal position. In addition to optimizing safety though careful needle placement, we emphasize the importance of precautions such as minimal to no sedation, confirmed needle placement through imaging techniques, and use of nonparticulate steroids [10]. Although prospective studies are needed to further investigate this technique, we would like to foster further discussion on its merits and drawbacks as compared with traditional transforaminal epidural approaches. The authors would like to thank Michelle Cooper and Franco Salas for assisting with the illustrations. Conflicts of interest: There was no direct or indirect support for this project.