Ultrasound Versus Fluoroscopy

Introduction

Peripheral nerve stimulation has been around since the early 1960s. These early stimulators were placed under direct visualization during an open surgical procedure. While the results were promising, the obvious disadvantages of having to place stimulators with open surgery prevented much further growth of the field until percutaneous placements began. Consequently, the first percutaneous placement of a peripheral nerve stimulator (PNS) did not take place until 1999, when Weiner and Reed first attempted to target the greater occipital nerves (GONs). These stimulators were placed percutaneously using C-arm fluoroscopy to accurately identify proximal landmarks such as the lamina of the C1 vertebrae to help approximate the GON. Alternatively, the earliest recorded use of ultrasound to place PNS leads was by Carayannopoulos et al. in 2009, who placed trial leads for patients with ilioinguinal neuralgia. Since that time, ultrasound- and fluoroscopy-guided techniques have been used for a variety of peripheral nerve targets, with varying degrees of success. The rest of this chapter will be dedicated to comparing and contrasting these imaging techniques.

Ultrasound Versus Fluoroscopy: The Basics

Open surgical placement of PNSs has the obvious advantage of direct visualization of nerves and surrounding structures during the operation. The disadvantages of this method, however, include significant morbidity associated with a surgical incision, the risk of damage to the nerve during dissection, and the length of the operation and potential need for general anesthesia (which inhibits intraoperative testing), as well as the inability to trial the patient first. Percutaneous approaches guided by fluoroscopy and ultrasound can help avoid these downsides, resulting in potentially safer and more accurate placement of PNS leads.

Fluoroscopy is the guidance technology most commonly used by pain specialists and was the first imaging method used to percutaneously place a PNS. Some of the advantages of using fluoroscopy include clear visualization of bony structures and higher resolution of structures at deeper levels. These can be quite beneficial when the nerve target runs proximal to or very near an osseous structure. Its disadvantages, however, include radiation exposure to both the patient and proceduralist. Additionally, its limitations lie in its inability to directly visualize discrete muscle layers, surrounding vascular structures, and targeted nerves. Lack of visualization of this anatomy can make precise depth of lead placement challenging and can lead to painful muscle stimulation, dysesthesias, and inefficient electrical coverage. It may also lead to inconsistencies when transitioning from trial to permanent implant. It also requires additional personnel to operate, is more expensive, and is less mobile than ultrasound. The utilization of ultrasound as an adjunct imaging modality can improve soft tissue anatomy visualization, provide more precise lead placement, and likely decrease the risk of the aforementioned complications.

Ultrasound guidance became popular in regional anesthesia for peripheral nerve blockade, where it has been shown to reduce complications and improve nerve block efficacy. These same principles can apply to ultrasound-guided placement of PNS, as it provides the ability to visualize anatomy and guide needle placement in real time. This allows for confirmation of intended needle path and avoidance of unnecessary trauma to arterial, muscular, and fascial structures, leading to fewer complications and less morbidity. This is particularly beneficial for peripheral nerves, as their course is variable, and anatomic landmarks can be imprecise. The less trauma and procedure-related pain that occurs, the more accurate a patient's perception of pain relief during intraoperative stimulation, improving localization and specificity of the trial.

No trial directly comparing ultrasound to fluoroscopy for PNS placement has been published; therefore, much of our data currently come from studies on peripheral nerve blockade. To that end, a randomized single-blind study comparing ultrasound to fluoroscopy for pudendal nerve block found similar accuracy and visualization of surrounding structures, but also found that the ultrasound-guided block took longer to perform. Another prospective randomized controlled trial comparing these two imaging modalities for genicular nerve block resulted in patients experiencing similar pain relief and functional improvement. Finally, Eichenberger et al. demonstrated ultrasound-guided third occipital nerve block to be similarly accurate to standard fluoroscopic block in 14 healthy volunteers.

Together, these studies suggest that, for select peripheral nerve targets, an ultrasound-guided approach is comparable to that of fluoroscopy. Although they have not been compared directly, ultrasound guidance has at least theoretical advantages over fluoroscopy for PNS lead placement and, as the next sections will demonstrate, is the only method described in the literature for many PNS targets.