The most common trajectories currently are the posterior approaches [12]. The first posterior approach is commonly referred to as a retrocrural celiac plexus block and is similar in injectate spread to a splanchnic nerve block. The term splanchnic nerve block is often used because it specifies that these are the nerves that are blocked on their way to the celiac plexus. This block, as the name describes, is performed with the final needle position near the anterior border of the T12 or L1 vertebral body and posterior to the diaphragm; it targets the greater, lesser, and least splanchnic nerves as they all come in close proximity. This technique avoids piercing the aorta, but it does require two needles on each side of the vertebral bodies. This is also a potential target for thermal neurolysis, which can be done with radiofrequency ablation. One does not generally attempt chemical neurolysis with these blocks given the potential for nerve root neurolysis.

The antecrural approach is, as the name implies, where the needle’s final position is anterior to the crus of the diaphragm. With this technique, there are several potential locations for the needle to reside in relation to the aorta, generally a distance 10 mm anterior to the anterior border of the vertebral body. The purpose is to be in a plane where the injectate can reach the celiac plexus without diffusing into the aorta. It can lie posterior to it in the retro-aortic space or lateral to it without piercing it. This latter approach, with the needle positioned lateral and adjacent to the aorta, is often described as the transcrural approach. On occasion with this approach, the needle is within the aorta as noted by blood return or contrast injection revealing an aortogram; in this situation, one can proceed with the transaortic approach.

The transaortic approach is performed with the needle positioned through the aorta at the T12 or L1 vertebral level until the needle is placed through and anterior to the aortic adventitia. This can be accomplished with one needle from the left side and is the preferred choice for chemical neurolysis. This particular approach is done with the provider using aortic pulsations to determine progress through the vessel. Practitioners can feel resonance through the needle, or they can attach low dead-space Luer-locking tubing with a length greater than the recorded blood pressure with conversion from mmHg to cmH₂O, and the column of blood can be seen pulsating until needle position is into the anterior aortic wall. At least another 2–4 mm of advancement is required to ensure that the needle does not remain in the intima, media, or adventitia, or any plane between; care must be taken to ensure that the needle is through the aortic wall to avoid the potential for aortic dissection during injection. The use of contrast and plunger pressure monitoring of injection can aid in reducing this complication.

In spite of the seeming danger, puncture of the aorta is actually relatively safe, and overall, major complications from celiac plexus block occur in less than 1% of patients [13]. Nonetheless, aortic dissection is one of the most concerning complications and has been reported to arise from use of the transaortic approach. Kaplan et al. described a fatal case of needle puncture in the anterior aortic intima between the superior mesenteric artery (SMA) and celiac artery causing dissection and vascular thrombosis that resulted in bowel and liver infarction [14]. Additionally, Naveira et al. reported an atheromatous aortic plaque presenting as a loss of resistance that also resulted in aortic dissection [15]. Because of the puncture of the aorta and the proximity of other vascular structures like the SMA and celiac and renal arteries, the transaortic approach is contraindicated in patients receiving anticoagulant medication and in patients with coagulopathy secondary to antiblastic chemotherapy or liver abnormalities, as they are at increased risk for retroperitoneal hemorrhage, a complication which is discussed in the previous chapter [16–18].

The posterior transdiscal approach involves passage of the needle directly through the T12–L1 or L1–L2 intervertebral disk via fluoroscopic or CT guidance. The needle is inserted 5–7 cm from the midline and directed to reach the paraaortic region at the level of the celiac trunk [19]. By traversing the intervertebral disk, this approach theoretically minimizes hazards of injury to the arteries and spinal cord, and potential damage to the liver, kidney, and pancreas as with other approaches can be avoided [20, 21]. It can also be used when the paravertebral needle path is obstructed by transverse processes or ribs or for improved access to the anterolateral wall of the aorta in patients with abnormal anatomy [16, 18, 19]. Although this procedure offers the possibility of avoiding vascular or organ trauma, it is not routinely used. There is increased risk for disk trauma that could lead to diskitis, herniation, meningeal puncture, and spinal cord puncture; this approach should be avoided in patients with degenerative disk disease in the thoracolumbar spine [16, 18, 19].

The celiac plexus can be approached from the ventral surface of the abdomen using CT guidance, MRI guidance, or ultrasound guidance. This approach can be more comfortable for patients who cannot lie prone with their pain or because they have a colostomy/ileostomy. In the anterior approach, the patient lies supine. The needle is inserted through the epigastrium at an entry site 1.5 cm below and 1.5 cm to the left of the xiphoid process [22]. The needle is advanced to a depth anterior to the aorta and the diaphragmatic crura between the roots of the celiac trunk and the SMA and most commonly traverses the stomach, liver, or pancreas before reaching the plexus [21, 22]. Although the anterior approach minimizes the risk of injury to the kidney and spinal cord, steps should be taken to prevent other complications [21]. It is essential to avoid major blood vessels, dilated biliary ducts, and portal hilum, and multiple punctures to the liver capsule can increase the risk of bleeding [21, 23]. Vascular structures in the neck of the pancreas must be avoided to prevent unnecessary bleeding [21]. Additionally, there have been reports of gastric perforation, pancreatic fistula, hepatic hematoma, retroperitoneal hematoma, paraplegia, and abscess with this approach [24–26]. While there is concern about contamination and potential infectious seeding, this approach, when done with a styleted and small needle (e.g., Chiba or Quincke), has been reported to be safe [5].

An endoscopic ultrasound-guided approach can be performed by endoscopists and generally is well-tolerated by patients. In a prospective randomized comparison of endoscopic ultrasound (EUS) and CT-guided celiac plexus block in 22 patients, the authors concluded that EUS-guided block provided more persistent pain relief than CT-guided block [27]. Advantages include a lack of radiation with EUS as compared to CT and costs. Challenges include visualization of deeper structures as intestinal air can impede sonographic imaging. Gastric perforation and infectious complications appear to be the most common complications associated with this approach. It can be more comfortable for patients and can also be combined with diagnostic endoscopic procedures [28, 29].

Based on the approach, the needle may pass near the nerve roots (posterior approaches) and kidney (posterior approaches), near or through the aorta (posterior approaches), through a disk (transdiscal), or through the bowel (endoscopic and anterior approaches). Structures nearby the celiac plexus that may be affected by all the approaches include other autonomic plexuses such as the cardiothoracic, superior hypogastric, and inferior hypogastric plexuses, as well as the artery of Adamkiewicz which supplies the spinal cord. Blockade of these structures can cause additional autonomic symptoms such as hypotension, sexual dysfunction, and bowel/bladder dysfunction.

There are few reports comparing the autonomic side effects of the different approaches to celiac plexus block [18, 21, 28, 29]. The differences are also varied based on volumes and doses of drugs used as well as the drugs themselves.

In addition to local anesthetics, adjuvants such as clonidine, while off-label, are used to prolong the duration of analgesia. Symptoms of bradycardia and hypotension may be augmented with the addition of clonidine. There is insufficient data to compare the different forms of denervation, such as alcohol or phenol neurolysis, or radiofrequency ablation. There are some limited data to suggest that, when comparing the two posterior approaches, hypotension is more common with a retrocrural approach and diarrhea is more common with the anterocrural approach [30]. Celiac plexus blocks are often repeated, and hypotension and diarrhea still appear to be the most common symptoms with repeat procedures [31].