Fig. 13.1
Celiac plexus parasagittal anatomy
Distal to the splenic flexure of the large intestine, the visceral-nociceptive fibers of the remaining colon (and of pelvic viscera) travel in part through the superior hypogastric plexus and lumbar splanchnic nerves to reach the spinal cord. The superior hypogastric plexus is a flattened band of intercommunicating fibers continuous with the intermesenteric plexus. It is found retroperitoneal and caudad to the inferior mesenteric artery near the abdominal aortic bifurcation, at the level of the L5/S1 vertebral junction. Since it carries not only sympathetic efferent fibers but also visceral afferent fibers from these abdominopelvic structures, the superior hypogastric plexus serves as a target in interventional pain medicine for visceral analgesia of the distal colon and pelvic viscera.
The pelvic splanchnic nerves (nervi erigentes) arise from S2 to S4 ventral rami and contribute parasympathetic fibers to the inferior hypogastric plexus (also called the pelvic plexus), where they continue through to ganglia in close proximity to the target pelvic viscera. This parasympathetic autonomic route also serves as another afferent visceral pathway.
The vagus nerve also carries visceral afferent information to the central nervous system (with associated cell bodies residing in the nodose ganglia); however, this information is thought to be for autonomic (parasympathetic) regulation, primarily. It is unclear at this time the degree to which, if any, the vagus afferent pathway is related to visceral nociception. There is evidence to suggest that vagal nerve stimulation may attenuate both somatic and visceral pain, possibly through descending inhibitory influences on the spinal dorsal horn neuron responses [11, 12].
The reader should also be aware of the existence of the enteric nervous system, which is the intrinsic nervous system of the gastrointestinal tract that functions autonomously to regulate autonomic gut function.
Sensitization of Visceral Afferents
Visceral afferent nociceptive pathways, as is the case with somatic afferents, may undergo sensitization after disease or inflammation. A general state of neuronal hyperexcitability results in decreased thresholds for firing, increased number of suprathreshold responses, and an increase in spontaneous electrical activity [13].
Visceral Pain Due to Abdominal Malignancy
Tumor burden from primary or metastatic disease may result in visceral pain through a number of mechanisms. For instance, visceral nociceptors respond to noxious mechanical stretch. This can occur in the setting of tumor growth in solid organ parenchymata, causing capsular distention, or in hollow organs, causing narrowing or obstruction with proximal tissue stretch. Ischemia from tumor invasion or compression of blood supply leads to an inflammatory response, characterized by the release of inflammatory mediators such as prostaglandins, bradykinin, and cytokines. This can in turn sensitize the visceral afferent system, amplifying nociception both peripherally and centrally. Neuropathic-type pain is due to compression or dysfunction of neural structures from direct or indirect tumor involvement. Visceral pain can be sequelae of cancer treatment as well, since there is often significant alteration in both structure and function of involved treatment areas. The following sections describe select cancer-related abdominal pain states both from tumor and in survivorship.
Select Abdominal Cancer Pain States
Gastric Pain
For the year 2013, the estimated new cases of stomach cancer in the USA is over 21,000, per SEER [2]. The majority (90 %) of gastric cancer type is adenocarcinoma. Risk factors for stomach cancer include the presence of Helicobacter pylori infection, chronic gastritis, and lifestyle factors (such as smoking or consuming smoked and pickled foods) [14].
Gastric cancer patients complain of burning and dull pain along the epigastrium or left upper abdomen. Tumor burden produces pain from distention, ischemia, compression, erosion, inflammation, and obstruction of the stomach and surrounding structures. Gastric and gastroesophageal (GE) junction cancer pain is managed primarily with a combination of nonopioid analgesics, opioid analgesics, and adjuvants, per World Health Organization (WHO) Analgesic Ladder guidelines [15]. Abdominal pain from gastric and GE junction cancer can also be managed by interventional pain techniques [3, 16, 17] such as thoracic splanchnic neurolysis or celiac plexus neurolysis, with absolute alcohol or 10 % phenol (in 20 % glycerin) as the neurolytic agent.
Treatment for primary gastric cancer depends on the TNM (Tumor, Node, and Metastasis) staging [18]. Radical surgery (subtotal or total gastrectomy with omentobursectomy and lymph node dissection) is the standard therapy for local disease, although neoadjuvant or adjuvant chemotherapy and/or radiation therapy may also be part of the treatment plan.
Hepatobiliary Pain
The estimated year 2013 incidence for hepatobiliary cancer in the USA is over 30,000 [2]. Hepatocellular carcinoma accounts for 90 % of all cases of primary liver cancer. Hepatitis viral infection (both hepatitis B and C) as well as hepatic cirrhosis from heavy alcohol consumption often precedes the diagnosis of liver cancer. Other associated risk factors include tobacco use and consumption of food contaminated with aflatoxins (metabolites produced from Aspergillus fungal strains) [1].
Gallbladder (and biliary tree) cancer, on the other hand, is less common, with year 2013 estimates for US incidence at approximately 10,000, nearly all adenocarcinomas [2]. Specific risk factors for both gallbladder and bile duct cancer have been identified as increased body mass index and cholelithiasis.
Visceral nociceptors found along the liver capsule, vasculature, and biliary system are activated by tumor growth through hepatic capsular distention, hepatobiliary duct obstruction, and vascular (portal vein or hepatic vein) obstruction. Patients describe the pain as located about the right side of the abdomen. It may be continuous or colicky. Pain may refer to the back or to the right shoulder, when diaphragmatic irritation occurs (this is referred pain via convergence of visceral and somatic afferents in the spinal cord dorsal horn).
Hepatobiliary cancer pain is managed primarily with a combination of nonopioid analgesics, opioid analgesics, and adjuvants, per WHO Analgesic Ladder guidelines. Patients with abdominal pain from hepatobiliary cancers may be candidates for thoracic splanchnic neurolysis or celiac plexus neurolysis with absolute alcohol or 10 % phenol (in 20 % glycerin) [19].
In patients with localized liver cancer, surgical resection is the recommended treatment. Depending on TNM staging, radiotherapy and/or chemotherapy systemically or via hepatic arterial infusion (HAI) may also be offered. Chemoembolization employs both HAI and distal hepatic arterial vessel occlusion (to increase regional drug distribution and dwell time in the tumor) by a number of materials, such as gelatin sponge, collagen, polyvinyl alcohol, starch microspheres, etc. and can be associated with abdominal pain during infusion. Local gallbladder cancer and bile duct cancer (cholangiocarcinoma) may be amenable to surgical resection; otherwise, unresectable disease may be treated with adjuvant chemotherapy and radiotherapy.
Pancreatic Pain
In 2013, over 45,000 people in the USA are diagnosed with pancreatic cancer. It is the fifth most common cause of cancer-related deaths in the USA [2]. Over 90 % of pancreatic cancers are ductal adenocarcinomas. Pancreatic cancer is associated with chronic pancreatitis, diabetes, smoking, obesity, and heavy alcohol use.
Patients with pancreatic cancer often complain of a dull epigastric pain radiating to the back. Visceral structures coaffected include the deep posterior abdominal wall, connective tissue, ducts, and vasculature. Pain is also attributed to associated bulky lymphadenopathy about the celiac axis.
Pancreatic cancer pain is managed primarily with a combination of nonopioid analgesics, opioids, and adjuvants, according to WHO Analgesic Ladder recommendations. Patients with abdominal pain from pancreatic cancer or pancreatitis often are good candidates for thoracic splanchnic neurolysis or celiac plexus neurolysis with absolute alcohol or 10 % phenol (in 20 % glycerin) [20, 21].
Surgical resection for pancreatic tumors is recommended for localized disease, although this accounts for less than one-fifth of patients at presentation [18]. Pancreatic cancer is generally considered resistant to standard chemotherapy and radiation therapy. Patients may be enrolled, however, in clinical trials.
Intestinal Pain
Cancer of the small intestines is relatively uncommon and accounts for less than 5 % of gastrointestinal malignancies. Colorectal cancer, however, is one of the most common cancers—in the year 2013 the number of those newly diagnosed in the USA with colon cancer is approximately 140,000, whereas the number for newly diagnosed rectal cancer is over 40,000 [2, 14]. Risk factors for colorectal cancer have been identified as follows: genetic predisposition, physical inactivity, high body mass index, high intake of alcohol and red meat, and low consumption of fruits and vegetables [1].
Patients with colorectal cancers present with pain from abdominal cramping and distention, and other symptoms such as bleeding. Treatment for abdominal pain from colorectal carcinoma includes standard therapy through WHO Analgesic Ladder guidelines. In addition, specific interventional pain techniques for the management of colorectal pain consist of the following: celiac plexus neurolysis for pain arising from small bowel cancer or large bowel cancer proximal to the colonic splenic flexure; superior hypogastric neurolysis for pain arising from colon cancer distal to the splenic flexure; and ganglion impar block for distal rectal pain [3, 22–24].
Related posts:
Gastroparesis: Pathophysiology of Chronic Abdominal Pain and Current Treatment
Chronic Abdominal Pain of Gynecologic Causes: Diagnosis and Treatment
Establishing Diagnosis of Chronic Abdominal Pain: Gastroenterologist View
Neurosurgical Options for Control of Chronic and Malignant Abdominal Pain
The Epidemiology of Chronic Abdominal Pain
Lessons Learned from Visceral Sensory Stimulation: Implications for Treatment of Chronic Abdominal Pain
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