Visceral abdominal pain is usually caused by stretching of fibers innervating the walls or capsules of hollow or solid organs, respectively. Less commonly, it is caused by early ischemia or inflammation. Severity ranges from a steady ache or vague discomfort to excruciating or colicky pain. Because the visceral afferents follow a segmental distribution, visceral pain can be localized by the sensory cortex to an approximate spinal cord level determined by the embryologic origin of the organ involved. For example, foregut organs (stomach, duodenum, and biliary tract) produce pain in the epigastric region; midgut organs (most of the small bowel, appendix, and cecum) cause periumbilical pain; and hindgut organs (most of colon, including the sigmoid) as well as the intraperitoneal portions of the genitourinary system tend to cause pain initially in the suprapubic or hypogastric area.
Because intraperitoneal organs are bilaterally innervated, stimuli are sent to both sides of the spinal cord, causing intraperitoneal visceral pain to be felt in the midline, independent of the right- or left-sided anatomic location of the involved organ. For example, stimuli from visceral fibers in the wall of the appendix enter the spinal cord at about T10. When obstruction causes appendiceal distention in early appendicitis, pain is initially perceived in the midline periumbilical area, corresponding roughly to the location of the T10 cutaneous dermatome.
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