Aisha Shaheen, MD, MHA and Marie Crandall, MD, MPH
Ms. Bradford is a 40-year-old female with no past medical history who presents to the emergency room with abdominal pain. She describes the pain as a dull ache that began after eating a heavy meal a few hours earlier. She has difficulty in pinpointing the exact location of the pain, although she states the pain seems centered on the midepigastric region. She incidentally notes pain around her right scapula. She has no other complaints.
On exam her vitals are unremarkable. She has minimal tenderness to deep palpation in the RUQ and no Murphy sign. You suspect a disease that causes visceral pain.
1. What 3 processes cause visceral pain in abdominal organs?
2. Based on the location of her pain, is this pain most likely to be caused by foregut, midgut, or hindgut disease?
3. What factors in this clinical scenario suggest that the source of her pain is visceral?
4. Why is this pain unlikely to represent acute cholecystitis?
ABDOMINAL PAIN OVERVIEW
1. Pain can be divided into 2 pathways: visceral pain and somatic pain. Visceral pain is the pain from afferent nerve fibers located in the abdominal organs. These fibers respond only to inflammation, ischemia, and distension. The signals from these nerves are perceived as dull, achy pain, in the midline and difficult to localize precisely.
Somatic pain, in contrast, is derived from somatic afferent fibers that are found in tissues such as skin, muscles, bones, and connective tissue. Somatic sensory afferent nerve signals are perceived as pain that is sharp and well localized. In the abdomen, somatic pain is caused by irritation of the nociceptive nerves in the parietal peritoneum. This can be caused by direct extension of inflammation from the visceral wall into the parietal peritoneum as occurs with acute cholecystitis or acute appendicitis. Somatic pain in the abdomen can also be caused by anything that irritates the peritoneum, including pus, blood, or gastrointestinal contents—or palpation of the inflamed tissue by the examiner. Unlike visceral pain, somatic pain can “lateralize” (ie, be perceived distinctly off the midline axis).
2. Visceral pain tends to be referred to areas corresponding to the embryonic origin of the affected organ. The abdominal viscera receive sensory fibers from the sympathetic chain, from T5 down to L3. Visceral pain is perceived as poorly localized pain in the corresponding dermatomal distribution. For example, foregut structures (the stomach, duodenum, biliary tree, liver, and pancreas) are innervated mainly by T5-T8. As a result, foregut pain is perceived as originating in the T5-T8 dermatome (which is the epigastrium). Biliary colic—pain that originates from distension of the gallbladder—is one such foregut process that causes visceral pain that is referred to this region. Visceral pain from midgut structures (small bowel, appendix, and proximal two thirds of the colon) results in pain in the mid-abdomen and periumbilical areas that correspond to the dermatomal distribution of T9-T11. Appendicitis is an example of a midgut process causing periumbilical pain (as long as it hasn’t advanced enough to cause peritoneal inflammation and hence somatic pain in the RLQ!). The distal third of the transverse colon down to the rectum are hindgut structures, innervated mainly by T12 to L3, with visceral pain from this area felt in the hypogastrium, or lower abdomen. “Gas pain” (due to distension of the colon) is the classic example (Figure 8-1).
Figure 8-1. The perceived locations of foregut, midgut, and hindgut visceral pain.
3. For Ms. Bradford, factors associated with visceral pain include the dull quality, the patient’s difficulty in localizing her pain, and the lack of significant findings on exam. Her complaint of right scapular pain is also interesting as it likely represents referred pain, a phenomenon associated only with visceral pain. Referred pain is pain perceived at a site remote from the location of the affected organ. It occurs when visceral sensory neurons converge in the spinal cord with nerve pathways that carry information from the somatic system. As a result of this convergence the vague visceral pain is “referred” as pain that is well localized to the sites innervated by these somatic nerves.
4. Whenever you approach a patient with abdominal pain, an understanding of the perception of pain can help you narrow your differential. Ms. Bradford’s history of postprandial pain in combination with what sounds like foregut visceral pain suggests she is suffering from biliary colic. Biliary colic is a classic example of visceral pain. The pain is caused by transient outflow obstruction within the gallbladder or cystic duct that causes a buildup in pressure within the gallbladder. That buildup of pressure and the subsequent distension cause visceral pain. As described above, only distension, ischemia, and inflammation cause pain in the hollow abdominal viscera.
It is useful to compare the pain associated with biliary colic with that of cholecystitis. If this was cholecystitis, the inflammation of the gallbladder and hence the peritoneum would have caused the patient to feel somatic pain, that is, sharp, lateralizing, and localized pain. That same inflammation is also the cause of the focal tenderness as seen, for example, with a positive Murphy sign.
TIPS TO REMEMBER
Visceral pain is dull, diffuse, and poorly localized and can be referred to distant sites.
Somatic pain in the abdomen involves irritation of the somatic parietal peritoneal nerves. It is sharp and well localized.
Foregut structures cause visceral pain in the epigastrium, midgut structures in the periumbilical area, and hindgut structures in the hypogastrium.
1. Which of the following types of pain is not associated with visceral pain?
2. Visceral pain from a midgut structure such as the appendix causes pain in which of the following areas?
B. Periumbilical area
D. Right lower quadrant
3. A Murphy sign is _______ pain.
1. C. Visceral pain is dull and diffuse, and causes referred pain. Somatic pain, in contrast, is well localized and can lateralize to 1 side or the other.
2. B. The appendix is a midgut structure and, as such, its visceral pain is felt in the periumbilical or middle abdominal area. RLQ pain is somatic pain associated with inflammation of the peritoneum overlying the appendix.
3. A. Inflammation of the peritoneum results in somatic pain because the peritoneum is innervated by somatic afferents. A Murphy sign results from palpation of the inflamed peritoneum overlying the gallbladder.