Abdominal pain is one of the most common complaints encountered by pediatric hospitalists. Despite this, the evaluation is often exceedingly difficult, and in many cases no definitive diagnosis can be made. The most urgent matter for the hospitalist initially is to rule out a life-threatening surgical emergency. If an acute abdomen is suspected based on history and physical, prompt surgical consultation is imperative.

Abdominal pain can be caused by inflammation of the abdominal organs themselves (or their visceral peritoneum) or by inflammation of the parietal peritoneum lying in proximity to the underlying inflammation. Irritation of the abdominal wall musculature can also lead to pain, and various extra-abdominal processes have been associated with abdominal pain (e.g. diabetic ketoacidosis or lower lobe pneumonia). Pain due to a process in the small intestine is usually felt in the midline around the umbilicus initially; as the inflammation progresses, the parietal peritoneum in the area of inflammation becomes involved, allowing better localization of pain. The classic example is appendicitis, with a dull periumbilical ache early in the course followed by a progressive shift of pain to the right lower quadrant as the inflammation evolves. Certain elements of the history and physical examination findings may help identify the cause of abdominal pain (Table 17-1).

The differential diagnosis of abdominal pain is extensive (Table 17-2). In addition to the typical history and physical examination, epidemiologic factors are extremely helpful in narrowing the differential diagnosis, including age, gender, season, locale, and the like. As stated above, a patient with peritonitis requires timely surgical evaluation. With several conspicuous exceptions, most patients with signs of peritonitis on examination progress to that point gradually. On history, these patients, if old enough, may report that the bumps in the road on the trip to the emergency department caused pain. These patients prefer to lie motionless and do not want their abdomens palpated. The examiner can check for signs of peritonitis immediately by “inadvertently” bumping the bed; a wince of pain from the patient is a sign that any movement at all is irritating to the inflamed parietal peritoneum. Bowel sounds may be hypoactive or absent at this late stage, reflecting an ileus. The abdomen may be rigid, and the patient may have voluntary or involuntary guarding, a mechanism to prevent painful manipulation of the underlying enflamed peritoneum. Patients with peritonitis are likely to have rebound tenderness; where the pain that is felt when the examiner releases the abdomen is greater than that caused by the palpation itself. Patients of any age who fit this classic description of an acute abdomen are highly likely to require surgical intervention and rarely need further evaluation such as laboratory tests or radiographic studies, except possibly to assess their surgical risk.

Unfortunately for physicians, most cases of abdominal pain are not this clear cut. For each disease process in the differential diagnosis, there is a wide range of severity. For example, a patient with severe constipation may be in extremis, whereas a patient with early appendicitis may have so little pain (or such a high tolerance for pain) that he or she is sent home without having had further workup. A full history and physical examination are paramount to determine the cause of the pain. It must be kept in mind that common benign diagnoses (e.g. viral gastroenteritis, constipation) occur commonly, but depending on the presentation are often diagnoses of exclusion. It is the examiner’s job to triage these patients appropriately while recognizing the red flags that point to less common entities or those that need more urgent evaluation or intervention.