Introduction

Lumbar transforaminal epidural steroid injections (TFESIs) are commonly used interventions with proven efficacy for the targeted treatment of various lumbar radicular pain presentations [1, 2]. Despite their extensive use, lumbar TFESIs are associated with varied risks and complications that must be recognized to preserve the safety profiles associated with these procedures [3–5]. The most feared complication is arterial compromise and spinal cord infarction that can result in anterior cord syndrome, paraplegia, conus medullaris syndrome, and other significant associated neurogenic sequela.

Anatomy

Understanding the intricate anatomy of the lumbar neuroforamen is essential for safe procedural technique when performing lumbar TFESIs. The lumbar neuroforamen is created by the superior and inferior articular processes dorsally, by the vertebral body and intervertebral disc ventrally, and by the vertebral pedicles inferiorly and superiorly [1, 2]. These openings serve as the exit for the spinal nerve roots and radicular arteries. While the lumbar neuroforamina vary in size depending on age, height, and weight, they are typically around 20 mm in height and 10 mm in width [6]. The dorsal and ventral nerve roots merge just inside the foramen and then exit as lumbar spinal nerves, each anatomically corresponding to the superior vertebral level i.e., L4 nerve exits from the L4–5 neuroforamen, L5 nerve exits from the L5–S1 neuroforamen, etc. Interestingly, the ligaments inside the vertebral foramen are also quite structurally intricate and serve to anchor the neurovascular structures in place and stabilize the foramen itself.

The primary blood supply for the cervical and thoracic spinal cord segments is derived from the anterior and posterior spinal arteries. This blood flow in the thorax is supplemented by intersegmental spinal arteries that originate from the posterior intercostal arteries. However, in the lumbar region, the intersegmental radicular arteries begin to feed directly into the anterior and posterior spinal arteries to supplement the blood flow [7] (Figure 33.1).

Most notably, the artery of Adamkiewicz (AKA), the largest of the intersegmental radicular arteries, joins the anterior spinal artery typically around T8–L1 to become the primary blood supply for the anterior spinal cord [1–5]. The AKA is identifiable on imaging by its unique hairpin turn in the spinal cord; vascular compromise of the AKA can lead to spinal cord infarction and anterior cord syndrome.

While most (89%) of the population’s AKA originates between T8–L1, angiographic and cadaveric studies have localized the AKA at every single lumbar level and as low as the L4–5 and L5–S1 neuroforamen [8]. Irrespective of the level at which it originates, the AKA and other radicular arteries are reliably located in the superior anterior aspect of the lumbar neuroforamen [7, 9] (Figures 33.2 and 33.3).

Unfortunately, this is the very same region standardly targeted in the ubiquitous “safe triangle” technique (Figure 33.4).

The original depictions of the safe triangle failed to include the vascular anatomy. The technique was widely disseminated before realizing the rare, grave, and finite risk of compromising blood flow to the entire thoracolumbar spinal cord [4, 10]. The results of well-designed CT angiography studies, cadaver dissections, and reviews of MRI imaging, have all revealed the consistency of the route of this vital radicular artery through the “safe triangle” before turning superiorly to anastomose with the anterior spinal artery.

While lumbar cord angiography may be the gold standard to localize the AKA and radicular arteries, and their location within the neuroforamen, such testing is not conventionally obtained prior to a lumbar TFESI.

Indications and Contraindications

The goal of a lumbar TFESI, relative to a lumbar interlaminar epidural steroid injection, is to selectively target the nerve root causing the patient’s painful radicular symptoms. Manchikanti et al. have also shown the efficacy of transforaminal injections in treating pain from spinal stenosis and discogenic pain [11]. Additionally, a TFESI can also serve as a diagnostic modality. For example, administration of local anesthetic agents to discrete nerve roots can help diagnose at-level radiculitis or radiculopathy [1, 2]. This diagnostic benefit is of significant utility to both interventional pain physicians and spine surgeons who can subsequently perform targeted, at-level TFESIs or neuroforaminal/laminar decompression, respectively.

Indications

• Lumbar radiculitis or radiculopathy
  
• Lateral recess spinal stenosis
  
• Degenerative disc disease
  
• Postlaminectomy changes

Procedural Techniques

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Complications of Opiate Therapy Complications of Obturator Nerve Block Complications of Cervical Discography Complications of Intradiscal Therapeutic Procedures Complications of Percutaneous Cordotomy Complications of Stellate Ganglion Block (SGB)