Abstract
Objective
Peripheral nerve stimulation provides targeted stimulation and pain relief within a specific nerve distribution. This technical case report provides a method to perform selective nerve root stimulation of thoracic and lumbar spinal nerves using ultrasonography.
Methods
Ultrasound-guided peripheral nerve stimulation of thoracic and lumbar spinal nerves allows better visualization of soft tissue anatomy and planning of needle trajectory.
Conclusions
Ultrasound-guided peripheral nerve stimulation procedures may provide a safer method for neurostimulation lead placement when compared with fluoroscopic-guided techniques.
Keywords: Peripheral Nerve Stimulation, Neuropathic Pain, Thoracic, Lumbar, Spinal Nerve Root, Ultrasound, Percutaneous
Introduction
Selective nerve root stimulation (SNRS) involves preferential stimulation of one or more dorsal spinal nerve roots directly and offers the advantage of both spinal cord stimulation (SCS) and peripheral nerve stimulation (PNS). It is theorized to provide more specific paresthesia to target pain in specific radicular distributions [1,2]. SNRS has been successfully used to treat painful diabetic or peripheral neuropathy, post-herpetic neuralgia, pelvic pain, interstitial cystitis, perineal pain of urologic origin, ilioinguinal neuralgia, discogenic back pain, and failed back surgery syndrome [1,2]. It is generally a very safe procedure but does contain the risk of injury to the nerve root itself. Most commonly cited complications include lead migration, lead breakage, and infection [1,2].
Technique
Thoracic Root
The thoracic spinal nerve immediately distal to the dorsal root ganglion can be targeted for PNS as it exits the intervertebral foramen. At this site, the nerve root is located anterior to the lamina and posterior-medial to the pleura.
Thoracic spinal nerve PNS is performed with the patient in a prone position using an appropriate aseptic technique. The appropriate thoracic level is identified using longitudinal transducer orientation and counting the ribs. The 12th rib is identified by moving the probe laterally until the rib shadow is no longer seen, and then the probe is moved cephalad to count the ribs and identify the thoracic level corresponding to the thoracic spinal nerve of interest.
Once the correct thoracic level is determined, the probe is rotated 90º into a transverse orientation to visualize the rib and transverse process of the desired vertebra at the costotransverse joint. The ultrasound probe should be translated medially to also bring the spinous process into view, creating a transverse paravertebral view of the vertebra. In this transverse view, the spinous process, lamina, transverse process, and rib can be visualized (Figure 1A). Then, the probe is moved caudally immediately inferior to the transverse process, which will also remove the rib shadow, exposing the hyperechoic pleura beneath (Figure 1B) and sometimes allow for visualization of the exiting spinal nerve as a faint hyperechoic structure anterolateral to the lamina (Figure 1C).
Figure 1.
Paramedian transverse ultrasound view at the targeted vertebra level. A) Initial view (top). B) Transition view as the ultrasound probe is moved caudally (middle). C) Final view of the target location inferior to the transverse process (bottom). *Expected location of spinal nerve. L = lamina; P = pleura; Sp = spinous process; Tp = transverse process.
A 25-gauge 3.8-cm needle is then used to provide skin anesthesia. Deep infiltration of local anesthesia should be avoided to decrease interference with muscle and nerve stimulation during testing.
An introducer with a stimulating probe is then inserted from lateral to medial using real-time sonographic visualization and advanced along the planned trajectory to within ∼5–15 mm of the targeted spinal nerve (Figure 2). Test electrical stimulation can now be applied via stimulating probe to assist in identifying the optimal location for the indwelling lead. At the time, the stimulating probe must be kept lateral to the border of the lamina to minimize risk of insertion into the neural foramen. The stimulating probe is connected to the stimulator, and the intensity is adjusted until comfortable sensations produced by the stimulator cover the regions of patient’s pain. Once the appropriate position is identified, the stimulating probe is replaced with the lead through the introducer needle. The lead should be visualized exiting the introducer needle, and stimulation testing should be done as the lead is advanced to a previously determined location. At this time, lead stimulation can be used to confirm coverage of the affected area. While placing manual pressure at the distal tip of the introducer, the introducer is then removed, causing the lead to be deployed and anchor into the tissue. Lead stimulation is again used to confirm appropriate coverage and ensure that the lead did not migrate during removal of the introducer. The lead is then secured and/or implanted as per specific manufacturer guidelines.
Figure 2.
Paramedian transverse sonographic view of the needle trajectory to the target spinal nerve. The needle tip can be seen ∼5 mm superficial to expected spinal nerve. *Expected location of spinal nerve; white arrow, needle. L = lamina; P = pleura; Sp = spinous process
At the discretion of the performing provider, fluoroscopy can be utilized for confirmation of appropriate placement of the needle and lead at the respective steps (Figure 3). Additionally, use of fluoroscopy is recommended in more technically difficult cases that may have limited ultrasound needle visualization. These cases include patients with a high BMI (usually >40), anatomical variations, and presence of hardware.
Figure 3.
Anteroposterior fluoroscopic view of the introducer needle with a stimulation probe that was inserted using sonographic guidance. The tip of the needle is located lateral to the T2 lamina.
Lumbar Root
The lumbar spinal nerve can also be targeted for PNS as it exits the intervertebral foramen. At this site, the nerve root is located anterior to the lamina and facet joint and posterior to the vertebral body.
With optimized patient positioning with abdominal roll to alleviate lumbar lordosis and proper aseptic technique, the transducer is placed in a midline transverse position, and the transition from the sacrum to the fifth lumbar spinous process is identified. Then, the appropriate lumbar vertebral level is localized by counting cephalad along the spinous processes. A paramedian sagittal view at the level of the transverse processes can also be utilized to view multiple levels to facilitate determining the correct vertebral level by counting cephalad from the sacral ala [3].
At the targeted vertebral level in paramedian transverse sonography, the transducer is moved laterally to visualize the spinous process, lamina, transverse process, and possibly the superior articulating process. The ultrasound probe is then moved slightly caudally immediately inferior to the transverse process, thus visualizing only the spinous process, lamina, and dorsolateral post of the vertebral body. The exiting spinal nerve can sometimes be seen as a faint hyperechoic structure anterolateral to the lamina. The shadow from the lamina can cause difficulty with visualization of the spinal nerve and vascular structures.
The lumbar spinal nerve can be targeted using an in-plane technique with a planned needle trajectory from lateral to medial with a depth no greater than the lateral border of the lamina. A cautious approach should be taken to insert the needle more lateral to the erector spinae muscle in order to decrease the chances of lead migration by muscle contraction. The percutaneous sleeve with a stimulating probe followed by the PNS lead can be placed using the technique described above.
Discussion
With advances in ultrasound technology and increased utilization of ultrasonography in pain medicine interventions, percutaneous peripheral nerve stimulation lead placement at the level of the spinal nerve is a reliable option to alleviate pain syndromes in specific dermatomal distributions.
Although similar procedures can be performed with fluoroscopy, ultrasound-guided techniques offer additional information and safety via visualization of the patient’s soft tissue anatomy, spinal nerve, and vascular structures, thus allowing for detection of individual anatomical variations. However, there are some limitations with ultrasound. Larger patient habitus and deeper anatomical structures can create difficulties with reliably visualizing the target. The shadow from the lamina can also cause difficulty with visualization of deeper spinal nerve and vascular structures. In conclusion, ultrasound-guided percutaneous peripheral nerve stimulation may be considered to safely provide targeted stimulation and subsequent pain relief within a specific peripheral nerve distribution.
Funding sources: This work was supported, in part, by the National Cancer Institute Cancer Center Support Grant P30CA008748.
Conflicts of interest: Akshat Gargya: There are no disclosures to report. Harmandeep Singh: There are no disclosures to report. Tiffany Lin: There are no disclosures to report. Amitabh Gulati: Consultant for Medtronic.
Supplement sponsorship: This article appears as part of the supplement entitled “Peripheral Nerve Stimulation: Update for the 21st Century” sponsored by Bioness and by SPR Therapeutics, Inc.
References
- 1. Stuart RM, Winfree CJ.. Neurostimulation techniques for painful peripheral nerve disorders. Neurosurg Clin N Am 2009;20(1):111–20. [DOI] [PubMed] [Google Scholar]
- 2. Levine AB, Steven DA, Parrent AG, MacDougall KW.. Successful long-term nerve root stimulation for chronic neuropathic pain: A real world, single center Canadian experience. Pain Physician 2017;20(2):95–106. [PubMed] [Google Scholar]
- 3. Chin KJ, Karmakar MK, Peng P.. Ultrasonography of the adult thoracic and lumbar spine for central neuraxial blockade. Anesthesiology 2011;114(6):1459–85. [DOI] [PubMed] [Google Scholar]