The intercostal nerves supply sensation to the thorax and abdomen. Prior to the widespread adoption of the thoracic epidural approach to provide analgesia following major thoracic and abdominal surgery, multiple intercostal nerve blocks were frequently used to provide postoperative pain control for common abdominal operations such as open cholecystectomy. In the postoperative setting, intercostal nerve block is rarely conducted with radiographic guidance. This is a simple technique that can be performed safely and effectively at the bedside using surface landmarks to guide placement. In contrast, neurolysis of the intercostal nerves has been used to provide long-lasting pain relief for patients with painful metastases involving the chest wall. Use of image-guided injection for neurolysis of the intercostal nerves can ensure that the neurolytic solution is injected at the level of the metastases and in close proximity to the intercostal nerves.

The intercostal nerves arise from the anterior primary rami of the first through 12th thoracic spinal nerves. The thoracic spinal nerves traverse through the intervertebral foramina to enter the paravertebral space (Fig. 14-1). The paravertebral space is bound by the pleura anteromedially, the vertebral body medially, and the transverse spinous processes and paravertebral musculature posteriorly. The ribs traverse this space and form two articulations with the vertebral bodies: the costotransverse articulation, where the rib contacts the transverse process, and the costovertebral articulation, where the head of the rib meets the vertebral body. The thoracic spinal nerve root traverses through the intervertebral foramen and ramifies into anterior and posterior branches; the anterior branch forms the intercostal nerve. The intercostal nerve traverses laterally to lie in the subcostal groove, a shallow notch along the inferior margin of each rib. Within this groove, the intercostal vein and artery lie in close proximity, just superior to the nerve (Fig. 14-2). This accounts for the high plasma levels of local anesthetic produced with intercostal nerve blocks. The costal groove becomes shallow and disappears altogether some 5 to 8 cm lateral to the posterior midline. The intercostal nerve may lie immediately below the rib margin or closer to the midpoint between ribs as it traverses laterally. The lateral branch of the intercostal nerve rises over the posterolateral chest wall anterior to the posterior axillary line (an imaginary line extending directly inferior from the posterior axillary fold). This is an important factor to understand because intercostal nerve blocks performed anterior to the posterior axillary line may not anesthetize this branch and may produce incomplete truncal anesthesia. The nerves continue anteriorly around the chest wall, ending in the anterior branches. These terminal branches supply sensation to the anterior chest wall. The critical soft tissue and vascular structures relevant to safely perform intercostal nerve block cannot be seen with fluoroscopy but are readily visualized with ultrasound (Fig. 14-3). Time-motion mode (M-mode) ultrasound also provides a sensitive and simple technique for detecting even the smallest pneumothoraces (see Fig. 14-3C). Description of ultrasound-guided intercostal nerve block is beyond the scope of this text, but this technique may well supplant the use of radiographic guidance as more practitioners gain expertise with ultrasound.

Multiple intercostal nerve blocks were frequently used to provide postoperative pain control for common abdominal operations such as open cholecystectomy, but thoracic
epidural infusion is simpler and provides effective continuous analgesia. The use of intercostal blocks has also been described for repair of small umbilical hernias, extracorporeal shock wave lithotripsy, and pacemaker insertion. The use of one- or two-level blocks remains an excellent means of providing anesthesia for chest tube insertion. Intercostal nerve block is a simple and effective means for relieving the pain of rib fractures, albeit limited to the duration of local anesthetic effect. Intercostal nerve blocks for treating pain in acute settings are usually carried out without radiographic guidance, using surface landmarks to guide block placement. Intercostal neurolytic blocks using phenol or alcohol have proven effective for treating painful, isolated metastatic lesions involving the ribs, and the use of radiographic guidance facilitates safe and effective intercostal neurolysis.