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Pain in the lower abdomen and pelvis is one of the most common patient complaints. In addition to the human costs of illness and distress, the economic results can be measured in billions of dollars from medical charges as well as lost wages and productivity. Accurate diagnosis and treatment offers an opportunity to minimize this toll.

Pain is subjective and often ambiguous, and thus, difficult to diagnose and treat. Therefore, clinicians should understand the mechanisms underlying human pain perception, which involves complex physical, biochemical, emotional, and social interactions. Providers are obligated to search for organic sources of pain, but equally important, they should avoid overtreatment for an illness or injury that is minor or short lived.

Pain is a protective mechanism meant to warn of an immediate threat and to prompt withdrawal from noxious stimuli. Pain is usually followed by an emotional response and inevitable behavioral consequences. These are often as important as the pain itself. Merely the threat of pain may elicit responses even in the absence of actual injury.

When categorized, pain may be considered somatic or visceral depending on the type of afferent nerve fibers involved. Additionally, pain is described by the physiologic steps that produce it and can be defined as inflammatory or neuropathic (Kehlet, 2006). Both categorizations are helpful in diagnosing the underlying sources of pain and selecting effective treatment.

Somatic Pain

Somatic pain stems from nerve afferents of the somatic nervous system, which innervates the parietal peritoneum, skin, muscles, and subcutaneous tissues (Fig. 23-3). Somatic pain is typically sharp and localized. It is found on either the right or left within dermatomes that correspond to the innervation of involved tissues (Fig. 11-1).

Figure 11-1

Dermatome maps. A dermatome is an area of skin supplied by a single spinal nerve. A. Body dermatomes. B. Perineal dermatomes. (Redrawn from Rogers, 2000, with permission.)

Visceral Pain

Visceral pain stems from afferent fibers of the autonomic nervous system, which transmits information from the viscera and visceral peritoneum. Noxious stimuli typically include stretching, distension, ischemia, necrosis, or spasm of abdominal organs. The visceral afferent fibers that transfer these stimuli are sparse. Thus, the resulting diffuse sensory input leads to pain that is often described as a generalized, dull ache.

Visceral pain often localizes to the midline because visceral innervation of abdominal organs is usually bilateral (Flasar, 2006). Also, visceral afferents follow a segmental distribution, and visceral pain is typically localized by the brain's sensory cortex to an approximate spinal cord level that is determined by the embryologic origin of the involved organ. For example, pathology in midgut organs, such as the small bowel, appendix, ...

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