The Carnett’s test is an easy way to determine if abdominal pain arises from abdominal wall. The test is considered positive when the palpation of the tender area results painful only when the patient tenses the abdominal wall by elevating the head and the shoulder or straight leg rising [4].

As suggested by Gallegos and Hobsley, the Carnett’s test well fits in the algorithm for abdominal wall pain diagnosis [6]. When positive and the painful area is located near or in correspondence of a surgical scar, an injection of local anesthetic is usually performed. The diagnosis of abdominal wall pain is confirmed only if the patient experiences immediate pain relief after the injection, otherwise different sources of pain should be sought [4, 6].

Differential neuraxial blockade is a temporary diagnostic block that takes the advantage of the variable effect of local anesthetics on different nerve fibers to identify the etiology of pain. The differential block is performed by the administration of placebo or local anesthetic through an epidural catheter. Hypothetically, leads to selection of the pain origin as psychogenic, sympathetic, nociceptive (sensory based), or central [10]. Nevertheless, the ability of differential neuraxial blocks to diagnosis of various categories of pain generation is unproved. Reviewing the literature, only two reports were found with weak evidence that differential neuraxial blockade can predict treatment response. Both reports evaluated only a small cohort of patients [11, 12].

The rationale behind the test is based on the different sensitivity of nerve fibers to local anesthetics, which is ultimately related to the anatomical and functional differences among the fibers such as size and myelination degree.

An alternative of the classical differential epidural block evaluates the ratio between pain and pinprick skin sensitivity during the recovery phase from a complete (surgical) epidural anesthesia in the dermatomes corresponding to pain irradiation [10]. A persistent pain relief when skin dermatomes anesthesia recedes indirectly defines the pain as visceral and points toward an intra-abdominal organ as the pain generator [10].

Limitation of this kind of test is due to the interaction between local anesthetic and nerve fibers and is a dynamic and unpredictable phenomenon that may be influenced by a multitude of factors. Also, overlap in the range of nerve fiber sizes makes it unlikely that any fiber type can be reliably isolated by this procedure. There is no guarantee that the surgical anesthesia achieved during the procedure blocks nervous transmission in all fibers and there is no evidence that sympathetic and visceral fibers are always slowest to return to normal function after the block [10]. For these reasons, the interpretation of differential epidural test sometimes could be very difficult. In addition, epidural differential block is a time-consuming technique and exposes patients to side effects and complications of a neuraxial blockade [13].

The distribution of sensory blockade is different with rectus sheath block, and Transversus abdominis plane (TAP) block. Rectus Sheath block is performed just below the costal margin at an angle of approximately 45° to the skin, in a plane between posterior rectus sheath and fascia transversalis. It provides sensory block for the whole midline of the abdomen. TAP block is performed laterally on the abdomen by placing local anesthetic in the plane between the internal oblique and transversus abdominis muscles. Bilaterally performed provides only reliable analgesia below the umbilicus.

Recent studies investigating abdominal wall pain in pediatric population proposed the use of Rectus Sheath Block and TAP Block in the management of CAWP [7, 14].

When the exact localization of the painful spot results to be difficult (i.e., pediatric population), Rectus Sheath Block represents an alternative to the infiltration of the point of maximum tenderness for both diagnosis and treatment of abdominal wall pain [7]. Due to the peculiar anatomical conformation of cutaneous nerve branches, however, Rectus Sheath Block might fail in one-third of the patients [7].

The TAP block allows to obtain a blockade of afferents originating from the anterior abdominal wall (skin, muscle, and parietal peritoneum), interrupting signals transmission travelling along the anterior rami of the lower six thoracic nerves and first lumbar nerve [15]. These nerves pass through a fascial plane between the internal oblique and transversus abdominis muscle called transversus abdominis fascial plane [9, 15]. A cadaveric and human study performed by McDonnell et al. shows that deposition of local anesthetic within the TAP produces a reproducible sensory block over the anterior abdominal wall from T7 to L1 dermatomes [11]. After initial description of, ultrasound-guided techniques of TAP, variation from the classic TAP block, the subcostal TAP block, has also been described; it is designed to provide more reliable coverage of the upper abdominal wall [16].

In 2009, Soliman and Narouze proposed the use of TAP block as a substitute of differential epidural block to distinguish visceral pain from abdominal wall (somatosensory) pain [12]. TAP block could replace differential epidural block because of a better side effects profile, especially when performed by an experienced physician with an ultrasound-guided technique [13]. Limitation of the use of TAP block in the differential diagnosis of abdominal pain is the difficulty to detect somatosensory pain which does not originate from the anterior abdominal wall.

Paravertebral nerve block is a useful tool in the differential diagnosis of abdominal pain [17]. The spinal nerves in this space are devoid of a fascial sheath, making them exceptionally susceptible to local anesthetics.

Paravertebral analgesia is achieved placing local anesthetic alongside the vertebral column in the paravertebral space, which is crossed by intercostal and sympathetic nerves [17]. Paravertebral block also provide large unilateral somatic (mean of five dermatomes) and sympathetic block (mean of eight dermatomes), including the posterior ramus in multiple contiguous thoracic dermatomes. Apart from strict longitudinal spread, other forms of distribution have also been observed [18].

Relative contraindications for paravertebral block are coagulation disorders, anticoagulation, tumor in the paravertebral space, and empyema [16]. Complications are mainly due to the close relationship of the paravertebral space to the pleura and the neuraxial structures: an incorrect needle placement might result in pneumothorax or in epidural/intrathecal spread of the local anesthetic [17, 19].

Richardson et al. performed a review of 12 published studies with a total of 538 patients, underwent bilateral paravertebral block indicates paravertebral block as a procedure that can provide good intra and postoperative analgesia not only for thoracic surgery but also during abdominal and gynecological surgery and in chronic pain management [17]. Naja et al. reported the effectiveness of paravertebral block in the treatment of refractory myofascial pain syndrome at thoracic level [20].

Chronic visceral pain was usually considered a “somatic” pain and therefore not suitable to be treat with treatments such as Spinal Cord Stimulation (SCS), which have been shown to be quite effective in treating chronic pain with the presence of a significant neuropathic component. Recent evidence, on the contrary, support the neuropathic origin of chronic visceral pain [21], which seems to be due to chronic sensitization of peripheral visceral nociceptors and wide dynamic range (WDR) neurons within the spinal cord [21].

Conventional pharmacologic therapy, sympathetic blocks, and radiofrequency application are important tool for the treatment of chronic visceral pain, but unfortunately they offer only a transient pain relief [22]. Since the first animal report of viscera-motor reflex suppression by the application of electrical stimulation to the spinal cord, the use of SCS for the treatment of chronic visceral pain significantly increased over time, in the attempt of providing a long-term therapeutic option [22].

In 2006, Tiede et al. [23] published a case report of two patients with refractory abdominal pain effectively treated with SCS; both patients had a history of several complicated abdominal surgeries with adhesions formation and subsequent surgical interventions for lysis of adhesions did not provide satisfactory pain relief.

Kapural et al. [22] in a survey performed in 2010 reported how the most common pathologies in patients with chronic abdominal pain treated with SCS were chronic pancreatitis, postsurgical intra-abdominal adhesions, and gastroparesis. Authors underlined how SCS is still rarely used despite its high therapeutic success rate; although the high cost of the device could be a matter of concern, there are scientific evidence to show how usually the cost of an SCS implant are overcome by the reduction in postimplant healthcare associated costs.

Kapural et al. also presented a case series of 35 patients suffering from chronic abdominal pain effectively treated with SCS, including 7 patients with chronic abdominal pain related to postsurgical adhesions [24]. A midline electrode placement at T5–T6 level was used in the majority of the patients, with exception of those patients suffering from lower abdominal quadrant pain who had electrodes placed at T11–T12 level. The reported percentage of patients with satisfactory (> 50 %) pain relief was around 86 %, and the success rate of the trial phase (86 %) was higher than the usual 60–70 % typical of other fields of SCS application [18]. Most of the patients who failed the SCS trial also had poor response to sympathetic nerves block and, on the contrary, patients with good response to sympathetic block also showed good results during the SCS trial [24]. As with most of the invasive chronic pain interventions, patient’s selection is crucial. In his works, Kapural selected the patients suitable for an SCS trial on the basis of the result of a differential epidural block and sympathetic block [22, 24, 25].

A percutaneous block of the sympathetic chain is often performed as a therapeutic measure in patients suffering from chronic pain refractory to conventional drug therapy or to avoid intolerable drugs side effects [26]. However, it can be also used in the decision-making process to assess patients suitability for SCS therapy, as previously suggested [22, 24], or to identify potential responders to thermal or chemical sympathetic neurolysis [25].

Thoracic sympathetic block are selected infrequently for neural blockade [27]. Indications for sympathectomy of thoracic ganglia include: CRPS I and II, neuropathic pain in thorax, chest wall, thoracic viscera, upper abdominal viscera, herpes zoster, postherpetic neuralgia, phantom breast pain after mastectomy, ischemia due to arterial occlusion, drug-resistant Raynaud’s disease, Burger’s disease, and injuries of upper extremities [24, 27]. Complications of thoracic sympathetic blocks are nerve root injury, spinal cord damage, and pneumothorax [27].

The preganglionic axons from T5 to T9 coalesce to form the Greater Splanchnic Nerve at the level of T9–T10, course through the diaphragm and end in the Celiac plexus, which extends for several centimeters in front and laterally around the aorta [25]; the preganglionic axons from T10 to T11 form the Lesser Splanchnic Nerve while the Least Splanchnic Nerve arise from T12 [25].

The Celiac Plexus block and the Splanchnic Nerves block are usually performed in case of upper abdominal pain due to malignant or nonmalignant conditions involving the gastrointestinal tract from the distal third of the esophagus to the transverse colon, the liver, the biliary tract, the adrenals, and the mesentery [25, 26]. Side effects include hypotension and diarrhea, whereas complications include but are not limited to nerve injury, paralysis, pneumothorax, bowel injury, and bleeding [25, 26, 28].

Indications for blockade of the celiac plexus or splanchnic nerves include cancer of the abdominal viscera [28] to the splenic flexure, and chronic benign abdominal pain refractory to pharmacological treatment [25]. Side effects include hypotension and diarrhea. Complications include but are not limited to nerve injury, paralysis, pneumothorax, bowel injury, and bleeding. A review of 31 studies involving 1,599 patients who received 2,750 Neurolytic celiac plexus block (NCPB) found that 85–90 % achieved good to excellent pain relief after NCPB. The efficacy and safety of NCPB are also supported by a meta-analysis of 24 studies [29]. Only two were randomized controlled trials, however. Long-term benefit was achieved in 79–90 % with upper abdominal pain, most frequently from pancreatic cancer. Six percent to 8 % may require a second block to achieve pain control. Some suggest that the efficacy of NCPB has not been established given that pre- and post-NCPB pain assessment data are lacking in many studies [30]. There is substantial published work to validate a grade “B” recommendation based on the validity of available evidence for NCPB as a reasonable therapy for cancer pain [31, 32].

Previous studies estimated the positive predictive value, for pain relief, of a diagnostic block to be 85 % and the negative predictive value to be 58 %; this implies that a negative diagnostic block may discourage a physician to consider a procedure on Celiac Plexus that could provide a more lasting pain relief [28]. Carroll indicates NCPB provides persistent augmented analgesia when used as an adjunct to systemic opiates, when used as a part of a comprehensive analgesic plan, but does not reliably decrease opiate requirements. He also indicates that splanchnicectomy under fluoroscopic guidance is the optimal approach to perform this block [28]. Also, Day [25] in his review about sympathetic block indicates the Celiac Plexus block/Sympathetic Nerves block as the only block concluded grade of recommendation 1B, with moderate-quality evidence for abdominal pain management.

The lumbar sympathetic chain lies at the anterolateral border of the lumbar vertebral bodies, and a block of the Lumbar Sympathetic Chain is usually indicated for CRPS I and II, peripheral neuropathy pain, and for ischemia-related pain [25]. A common side effect is hypotension due to peripheral vasodilatation; complications include bleeding, nerve root injury, genitofemoral neuralgia, paralysis, neuraxial injection, and renal puncture [25].

The Superior Hypogastric Plexus is a retroperitoneal structure located slightly left off the midline from the level of lower L3 lumbar vertebral body to the upper S3 sacral vertebral body near the bifurcation of the common iliac vessels [25]. The plexus branches descend into the pelvis as the Inferior Hypogastric Plexus receives parasympathetic fibers from S2 to S4 sacral level and forms the pelvic, middle rectal, vesicle, prostatic, and uterovaginal plexus [25].

The Superior Hypogastric Plexus block is indicated for cancer and noncancer pain originating from the descending colon to the rectum and for the urogenital system in the pelvis [25, 26]. Complications include intravascular injection, discitis, neuraxial injection, urinary tract injury, and bladder/bowel incontinence [25].

Ganglion impar (also known as Walther’s Ganglion) is the terminal ganglion of the sympathetic chain. Its anatomy is variable but is usually located caudal of the sacrococcygeal junction [25]. The Ganglion Impar block is usually indicated for vulvar pain, chronic perineal pain, and sacrococcygeal pain [25, 26].

Literature report few data about effectiveness of sympathetic blocks in the treatment of abdominal pain, and the available studies are of poor quality (only Celiac Plexus block/Splanchnic Nerves block shows a grade of evidence 1B) [25], due to the lack of well-designed RCTs with a sufficient number of enrolled patients. Pain physicians however continue to perform these procedures based on their everyday clinical experience with good results, reduced oral drug requirements, and safe side effects profile. In addition, sympathetic blocks play a fundamental role in the decisional algorithm for chronic abdominal pain treatments—as proposed by Kapural for the selection of potential SCS candidates [24].

The use of neurolytic blockade is still playing an important role in controlling cancer pain in selected patients. No neurolytic agent or technique has been proven to be superior to another. Current evidence suggests that patients with pain of malignant origin may benefit from a variety of neurolytic techniques, mainly for visceral pain control [33]. Those techniques interrupt the sympathetic nervous system at the ganglion level, where afferent fibers from abdominal and pelvic organs converge, to treat chronic pain of various, but cancer-related etiologies [33].

A neurolytic block of the sympathetic plexus or chain may maximize the analgesic effects of conventional therapy, reducing the opioid daily dose and consequently minimizing the side effects. This approach is particularly useful in the treatment of cancer pain patients, where an aggressive therapeutic approach may be justified despite significant side effects [34].

There are several techniques on how to perform truncal neurolytic ablation, among which the Interpleural Phenol block, the Celiac Plexus block, Superior Hypogastric Plexus block, and the Ganglion Impar block, are used the most [34].

To perform an Interpleural block, local anesthetic is injected into the thoracic cage between the parietal and visceral pleura, producing an ipsilateral somatic block of multiple thoracic dermatomes together with the block of the sympathetic chains and the splanchnic nerves [35]. It provides relief from surgical and nonsurgical pain originating from the chest and upper abdomen in acute and chronic settings [35].

The Interpleural Phenol block provides an effective technique for the treatment of visceral pain originating from esophagus, liver, biliary tree, stomach, and pancreas [34, 35]. Although the evidence for interpleural block in chronic pain derives mostly from case reports and care series, the use of interpleural block is suggested in many painful disorders including esophageal cancer pain and chronic pain in patients with upper abdominal cancer and chronic benign and neoplastic pancreatic pain [36]. It can also represent a valid alternative to celiac plexus block in selected patients where the celiac block is too difficult or unsafe to perform [36]. Pneumothorax and phrenic nerve palsy resulting in respiratory failure are known complications of the technique [34]. To make a block neurolytic, increased concentration of phenol are used, starting with the initial recommended dose of 5–10 ml of 6 % phenol with a subsequent progression in concentration (up to 10 %) [34]. In patients with severe refractory pain (i.e., cancer patients) are also suggested the use of local anesthetics (i.e., Bupivacaine or Ropivacaine) with continuous or intermittent bolus infusion [34].

The celiac plexus receives parasympathetic fibers from the vagus nerve and autonomic fibers supplying liver, pancreas, gallbladder, stomach, spleen, kidneys, intestines, and adrenal glands [34].