B. Parietal pain
Parietal peritoneum is innervated unilaterally via the spinal somatic nerves that also supply the abdominal wall. Unilateral innervation causes parietal pain to localize to one or more abdominal quadrants (e.g., inflamed appendix producing parietal peritoneal irritation).
Parietal pain is sharp, severe, and well localized.
Parietal pain is triggered by irritation of the parietal peritoneum by an inflammatory process (e.g., chemical peritonitis from perforated peptic ulcer or bacterial peritonitis from acute appendicitis). It may also be triggered by mechanical stimulation, such as a surgical incision.
Parietal pain is associated with physical examination findings of local or diffuse peritonitis and frequently signifies the need for surgical treatment.
C. Embryologic origin
Embryologic origin of the affected organ determines the location of visceral pain in the abdominal midline.
Foregut-derived structures (stomach to the second portion of the duodenum, liver and biliary tract, pancreas, spleen) present with epigastric pain.
Midgut-derived structures (second portion of the duodenum to the proximal two thirds of the transverse colon) present with periumbilical pain.
Figure 11-1. Frequent sites of referred pain and common causes.
Hindgut-derived structures (distal transverse colon to the anal verge) present with suprapubic pain.