1. What are the three afferent relays that mediate perception of abdominal pain?

Visceral abdominal pain is produced by stimulation of nociceptors located in the walls of the abdominal viscera. Somatic abdominal pain is produced by stimulation of nociceptors located in the parietal peritoneum and intraabdominal supporting structures. Referral pain occurs when strong visceral impulses enter the spinal cord at the same level as afferents from other areas; this is mistakenly “read” as pain arising from the second area (e.g., shoulder pain in gallbladder disease).

2. Can abdominal pain have any other causes?

As well as arising from abdominal structures, pain can be felt in the abdomen and yet be generated by distant structures. In the same way as abdominal pathology can cause a pain to be referred elsewhere in the body, irritation of distant structures can cause a pain to be referred to the abdomen. For example, pathology of the thoracic vertebra can be referred to the abdomen, giving the mistaken impression that intraabdominal problems exist. If the causal lesion is midline, then the referred pain can be to both sides of the abdomen. Similarly, irritation of thoracic nerves can cause radiation of neuropathic pain to the abdomen. For example, intercostal neuralgia will produce pain in a dermatomal distribution of the involved nerve, which, if arising from a lower intercostal nerve, will then be felt in the abdomen. Because allodynia is one of the features of neuropathic pain, care must be taken to ensure that intense pain on palpation of the abdomen is not in fact allodynia.

3. How can visceral, somatic, and referred abdominal pain be clinically distinguished?

Visceral pain tends to be poorly localized and felt in the midline, and it is often experienced as a dull soreness that fluctuates in severity. Visceral pain can be very difficult for patients to describe and may be referred to as an aching, gnawing, burning, or cramping discomfort or as pain commonly attended by restlessness and associated symptoms of autonomic disturbance (i.e., nausea, vomiting, diaphoresis, and pallor).

In contrast, somatic pain is typically more acute, intense, sharp, localized, and aggravated by movement.

Referred pain combines features of both visceral and somatic pain and is well localized in areas distant from the precipitating stimulus.

4. Can the location of abdominal pain be useful in determining the origin of the problem?

Information on the location, depth, and radiation of pain can provide helpful clues, but can also be misleading. Pain mediated along visceral afferent pathways tends to be poorly localized and referred to the midline, regardless of the lateral location of the pathologic process. However, the level of midline pain can provide helpful clues. Pain from gastroduodenal and hepatobiliary structures is usually perceived in the epigastrium; pain from the small bowel is usually periumbilical; and pain from the colon tends to be perceived in the lower abdomen.

5. What four classes of stimuli generate abdominal pain?

The abdominal visceral organs are insensitive to many stimuli that would ordinarily provoke cutaneous pain such as burning, pinching, stabbing, and cutting. The abdominal visceral organs generate pain in response to the following four general classes of stimuli:

6. The paucity of visceral afferent nerves and the bilateral symmetric innervation of most abdominal organs results in abdominal pain that is poorly localized and midline. What is the significance of abdominal pain that is clearly lateralized?

Clearly lateralized abdominal pain may arise either from one of the few intraabdominal organs with predominant one-sided innervation (e.g., kidney, ovary, ureter) or from structures with somatic rather than visceral innervation.

7. What determines where in the abdomen pain is experienced?

Afferent nerves from the abdominal viscera enter the spinal cord at different levels, and the level of entry governs where within the abdomen pain is experienced. Foregut structures, including the distal esophagus, stomach, duodenum, pancreas, liver, and biliary tree, are innervated by spinal segments T5–T6 to T8–T9 and manifest pain between the xiphoid process and umbilicus. Midgut structures, including the small bowel, appendix, and colon up to the distal transverse part, are innervated by spinal segments T8–T11 and L1 and manifest pain in the periumbilical region. Hindgut structures, including the distal colon and rectum, are innervated by spinal segments T11–L1 and result in pain between the umbilicus and pubic symphysis.

8. What historical attributes must always be enquired of when obtaining the history from a patient with abdominal pain?

The mnemonic PQRST provides a framework that ensures a full exploration of a given patient’s abdominal pain:

In addition, any relationship to other associated gastrointestinal symptoms (e.g., vomiting, diarrhea) or dysfunction of other contiguous organ systems (e.g., genitourinary or thoracic) must be sought.

9. Is chronic abdominal pain purely a disease of adults?

No. More than one third of children complain of abdominal pain lasting 2 weeks or longer. Commonly, simple issues such as constipation are the cause. In general, the response to an empirical course of medical management may give a higher yield than an exhaustive diagnostic workup. Employ behavioral, psychological, and nutritional strategies.

10. What historical symptoms suggest the presence of an uncomplicated peptic ulcer?

Peptic ulcer pain is commonly described as a burning or gnawing pain in the midepigastric or subxiphoid region. Occasionally patients with peptic ulcer deny any pain and complain of discomfort and distress with a “hunger” or “empty stomach feeling” in the epigastrium. Peptic ulcer pain may vary from patient to patient, but is commonly classic for a given patient and occurs in an episodic and rhythmic fashion. Episodic pattern refers to the way in which ulcer pain recurs over a long period of weeks, months, and years. Rhythm refers to the pattern in which pain recurs during a 24-hour period, typically adhering to the sequence of pain-food-relief. Ulcer pain typically occurs when the stomach is empty and is relieved by eating or drinking, especially for ulcers located at or near the pyloroduodenal junction. Pain from more proximal ulcers may be exacerbated by eating.

11. A 39-year-old man with a history of duodenal ulcer experiences sudden, severe pain throughout his abdomen. What may have happened?

Any alteration in the previous pattern of pain in a patient with a peptic ulcer should raise the suspicion of perforation. Acute free perforation (see Question 12) occurs suddenly and with almost immediate peak intensity. Severe pain may be felt throughout the abdomen and may be referred to the shoulders or flanks and lower abdomen. Physical examination demonstrates abdominal wall rigidity and involuntary guarding related to peritoneal irritation. In extreme cases of peritonitis, the abdominal rigidity is boardlike.

Note that palpation for muscular rigidity and guarding must be gentle. Do not attempt to elicit “rebound tenderness,” because it can be misleading, may cause the patient significant discomfort, and provides no more information than can be obtained using gentle palpation for underlying muscular rigidity.

12. What clinical features suggest the complication of ulcer penetration?

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