Evaluation of the patient with acute abdominal pain requires a careful history and physical examination by a skilled physician in conjunction with selective diagnostic testing. Acute abdominal pain is the most common general surgical problem presenting to the emergency department. Acute abdomen is defined as a recent or sudden onset of abdominal pain. This can be new pain or an increase in chronic pain. The differential diagnosis includes both intra- and extraperitoneal processes. The acute abdomen does not always signify the need for surgical intervention; however, surgical evaluation is warranted.
I. Pathophysiology of Acute Abdominal Pain
The abdomen is analogous to a box. Although this chapter focuses on pathophysiology inside the box, one must be cognizant of the fact that pathology on the surface of the box (e.g., rectus sheath hematoma) or even outside the box (e.g., testicular torsion) can present as abdominal pain. Abdominal pain arising from intra-abdominal pathophysiology originates in the peritoneum, which is a membrane comprising two layers. These layers, the visceral and parietal peritoneum, are developmentally distinct areas with separate nerve supplies.
A. Visceral pain
Visceral peritoneum is innervated bilaterally by the autonomic nervous system. The bilateral innervation causes visceral pain to be midline, vague, deep, dull, and poorly localized (e.g., vague periumbilical pain of the midgut).
Visceral pain is triggered by inflammation, ischemia, and geometric changes such as distention, traction, and pressure.
Visceral pain signifies intra-abdominal disease but not necessarily the need for surgical intervention.