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?
Abdominal Pain Overview
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).
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 ...