Mert Akbaş MD, FIPP and Gözde Dağıstan MD Akdeniz University School of Medicine, Antalya, Turkey An epidural steroid injection (ESI) is a minimally invasive and effective procedure frequently used for several conditions such as thoracic disc herniation, radiculopathy, spinal stenosis, postlaminectomy syndrome, and cancer pain. ESI has been in use since 1952 [1]. Corticosteroids diminish inflammation, suppress neuronal discharge, and desensitize dorsal horn neurons [2]. The spinal cord extends down to the level of L1–L2 in adults while the dural sac extends to the level of the 2nd sacral foramen. The epidural space extends from the foramen magnum to the sacrococcygeal hiatus. The width of the posterior epidural region is 1.0–1.5 mm in the cervical region, 2.5–3 mm in the upper thoracic region, 4.0–5.0 mm in the lower thoracic region, and 5.0–6.0 mm in the lumbar region [1]. The posterior epidural space involves the connective tissue and the ligamentum flavum. The main content in the epidural space is adipose tissue. Moreover, the epidural space contains the spinal branches of the segmental arteries, the internal vertebral venus plexus, lymphatics, and the dura arachnoid projections that enclose the spinal nerve roots [1]. Ligamentum flavum is suggested to be separately located on the right and left sides and join in the midline. However, fusion defects at varying degrees on the ligamentum flavum in the midline were demonstrated in the thin cross-sections of the epidural space. Further, ligamentum flavum joins the capsule of the zygapophyseal joint that is located at the same level on the lateral side [4]. The medulla spinalis is supplied by an anterior spinal artery (ASA) and two posterior spinal arteries (PSA). The largest of the anterior radicular arteries supplying blood to the lower thoracic and lumbar parts of the medulla spinalis is named “Adamkiewicz Artery”. Although this artery has several anatomic variations (may arise from between T6–S2), it often arises from the level of T9–T12 and usually from the left side in most people [5, 6]. Thoracic interlaminar procedures are more prone to complications compared to the lumbar region due to anatomic differences. The spinous processes of the thoracic vertebrae angulate downward and narrow down the thoracic interlaminar space (Figure 24.1). The vertebral columns are kyphotic in the thoracic region. Moreover, the thoracic epidural space is narrower than the one in the lumbar region. Therefore, the distance between the laminae and spinal cord is shorter. Figure 24.1 Thoracic vertebral column. (a) Oblique view. (b) AP view. The patient is placed in prone position. For the thoracic interlaminar blockade, the pillow is placed below the chest to allow expansion of the interlaminar space. The thoracic region is prepared and draped in sterile condition. After checking the level on the true AP view (spinous processes should be on the midline), the C-arm is rotated in the cephalad or caudad direction to open up the interlaminar space. The paramedian or median approach can be used for interlaminar injection. The technique varies according to the level of the block in the thoracic region. A median approach can be used between the C7–T5 and T9–L1 levels. Nevertheless, the paramedian approach is easier in the middle thoracic region (T5–9) due to the angle of the spinous processes. The spinous processes of the thoracic vertebrae angulate downward. The target needle entry point is 1 or 1.5 vertebral body height inferior and approximately 1–2 cm lateral to the midline for the paramedian approach. After infiltration of local anesthetic to the skin, the needle is advanced toward the midline of the interlaminar space. The needle entry angle is around 15–20 degrees on the coronal plane between the needle and skin. Then the C-arm is rotated laterally. When the top of the needle reaches the spinolaminar line, the needle should be advanced slowly until the loss of resistance is obtained (Figure 24.2). Figure 24.2 Loss-of-resistance and bounce technique. The needle tip should be seen just ventral to the spinolaminar line (the base of the spinous process) on the lateral view. The AP view must be rechecked to confirm the needle’s direction (Figure 24.3). Then, the contrast agent is injected to verify the needle position. When the needle tip arrives at the posterior epidural space just ventral to the spinolaminar line, the contrast agent flows dorsally along the spinolaminar line (Figure 24.4). After confirming correct placement of the needle, a mixture of local anesthetic and steroid is injected. Figure 24.3 Thoracic epidural injection (T9–10). Needle’s direction in the AP view. Figure 24.4 Thoracic epidural injection (T9–10). Contrast spreading along the spinolaminar line in the lateral view. The complications of interlaminar injection may be categorized as: 1. Spread of the contrast agent into soft tissues When the contrast agent is delivered right after the needle is placed, it may spread to soft tissues such as muscle ligaments rather than the epidural space (Figure 24.5). The needle tip may be in the posterior or lateral side of the spinolaminar line. In this case, the contrast agent spreads in parallel to muscle fibers or ligaments. This image can be easily distinguished before it spreads to the epidural space. However, repeated spread of the contrast agent into the wrong areas may make it difficult to see the needle tip, which may ultimately lead to dural puncture. For that reason, it is safer to select the next needle entry point in the caudal or cephalad direction. Figure 24.5 Contrast spreading to muscle. (a) AP view. (b) Lateral view. (Source: By permission from Dr Irene Kouroukli MD, FIPP.) 2) Intravascular injection
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Complications of Thoracic Interlaminar Steroid Injection
Introduction
Indications
Contraindications
Anatomy of the Epidural Space
Technique
Thoracic Epidural Block
Complications
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