Abdominal pain is one of the more common complaints in childhood, and it is important to distinguish between causes requiring surgical treatment and those that do not.

The age of the child has an important bearing on the diagnostic strategy: infants and young children cannot indicate directly that they are in pain. Irritability, anorexia, or vomiting are often indicators of pain, but abdominal tenderness can be difficult to elicit in a sick and unco-operative child or infant. Administration of a non-analgesic sedative such as chloral hydrate may be helpful in blunting the pain without masking its presentation. It is necessary to gain the confidence of older children, so that the maximum amount of information can be obtained and to enable repeat examinations to be performed with the minimum amount of difficulty.

The use of laboratory tests and imaging studies should depend on the results of history and clinical examination. Relatively simple procedures, such as complete blood count, urinalysis, and supine and upright radiographs of the abdomen and chest, are usually sufficient to establish a diagnosis.

Acute abdominal pain is second only to fever as the most common complaint presenting to paediatric emergency services. The most serious conditions are those which will cause rapid deterioration unless surgery is undertaken: these must be differentiated from those not requiring urgent surgical treatment. Unfortunately, the signs and symptoms of a problem requiring emergency surgery overlap with those of less serious conditions. In addition, the so-called classical presentation of many specific diseases requiring surgical treatment is not seen in paediatric patients.

Symptoms of an abdominal condition requiring surgical treatment are usually progressive; diffuse abdominal pain and tenderness become more localized, eventually becoming associated with rebound tenderness. Pain is usually steady for at least 6 h. Nausea, vomiting, and anorexia are almost always present, but are usually preceded by the onset of pain. While high fever is commonly associated with conditions that respond to conservative treatment, those requiring surgical intervention are often characterized by no, or only slight elevations in temperature.

Acute appendicitis is the most common childhood disease requiring surgical intervention. While the true incidence is unknown, about 10 per cent of children develop appendicitis, most commonly in the adolescent and prepubertal years. Appendicitis is rare before the age of 2 years.

The classic presentation is vague, periumbilical, crampy pain progressing to constant well-localized pain and tenderness in the lower right quadrant of the abdomen. This is followed by fever, nausea, vomiting, anorexia, and leucocytosis. The process typically evolves over 12 to 36 h: more rapid evolution is indicative of a gangrenous appendix and faecolith, with imminent perforation. This classic presentation is, however, unusual, particularly in younger children. Retrocaecal appendicitis may cause no abdominal wall tenderness or anorexia. Similarly, generalized peritonitis may be found at surgery in an infant displaying only irritability, discomfort on movement, and, perhaps, flexed hips. Appendicitis must, therefore, be considered in any ill-looking child in whom the results of an abdominal examination are abnormal and changing, and when there is no obvious cause.

Peritonitis is indicated by the presence of a board-like abdomen, and further diagnostic tests are usually unnecessary. If a perforated viscus, obstruction with strangulation, or ruptured ectopic pregnancy are likely causes, emergency surgical intervention is essential to enable further diagnosis or treatment.

In children under the age of 2 years, midgut volvulus secondary to intestinal malrotation is life-threatening. Such patients have often been perfectly healthy, and then develop sudden abdominal distension and vomiting, with a rapid deterioration in their condition. Radiographs show distension of an otherwise airless abdomen; gastrointestinal series show typical corkscrewing of the displaced duodenum. Immediate surgical intervention is necessary.

Intussusception is one of the most common causes of abdominal pain in children under the age of 2 years. Episodic severe, colicky pain is manifested by screaming and flexing of the legs on to the lower abdomen. Between episodes the child is quiescent and often exhausted. A tender mass in the right upper quadrant is palpable in about two-thirds of patients. When symptoms have been present for more than 24 h, bleeding per rectum is common, with the production of ‘redcurrant-jelly’ stools. Plain film radiographs of the abdomen may appear normal in children with intussusception, and a barium enema should be performed unless signs of peritonitis are present. The intussusception is often reduced by a barium enema performed within 24 h of onset. Surgery is required if this approach fails, if peritonitis is present, or if intussusception recurs.

Hirschprung's disease may cause abdominal pain secondary to obstipation from retained faeces. In very young infants obstruction may be severe enough to progress to severe dehydration, hypotension, intestinal perforation, and generalized peritonitis. Once the diagnosis has been made colostomy is required, with a definitive pull-through procedure being performed at a later date.

Gastroenteritis in children may present with severe, diffuse, and crampy abdominal pain. Such patients usually have abdominal distension, fever, and diarrhoea. The presence of headache, chills, and a very high temperature favours a viral aetiology.

Bladder infections and pyelonephritis may also cause severe abdominal pain as well as abdominal tenderness. The diagnosis of pyelonephritis is suggested by the presence of back pain, high fever and chills, nausea, and vomiting. Children with such an infection often require admission to hospital for intensive hydration and antibiotic treatment once the causative organism has been identified. Cystitis may present with abdominal pain, dysuria, frequency, urgency, and abnormal results of urinalysis and culture. Renal calculi, although rare in children, also cause severe pain related to the level of obstruction. This is usually in the flank and is associated with costovertebral angle tenderness.

Pancreatitis in children with no family history of the condition is usually related to trauma, although it may also be associated with abnormalities of the ampulla of Vater or the duct of Wirsung. Patients with pancreatitis present with steady epigastric pain, often radiating to the back, abdominal tenderness, and elevated serum amylase levels. Gallbladder disease should be ruled out in these patients, especially if there is evidence of cholangitis, with or without jaundice. Cholelithiasis with cholecystitis should be suspected in a child with pain in the right upper quadrant, anaemia, and a family history of gallstones or biliary colic.

The clinical picture of Yersinia enterocolitis, with fever, vomiting, and abdominal tenderness, may suggest a condition requiring surgical intervention. Infections by other gastrointestinal pathogens are usually characterized by high fever and diarrhoea. Stool smears and cultures are helpful in making the correct diagnosis.

Lower lobe pneumonia is frequently overlooked as a cause of acute abdominal pain in children. Streptococcal pharyngitis or tonsillitis can also cause abdominal pain. Diabetic ketoacidosis may initially present with severe abdominal pain, nausea, vomiting, and anorexia. Severe abdominal pain may also be associated with acute rheumatic fever, Henoch-Schönlein purpura, haemolytic-uraemic syndrome, and sickle-cell disease.

In children with immunodeficiency or nephrotic syndrome, an acute abdomen may be a sign of primary peritonitis. A diagnostic paracentesis may indicate the presence of antibiotic-sensitive organisms in the peritoneal cavity, and unnecessary surgery can be avoided. If Gram-negative rods are isolated, however, appendicitis may be present and further surgical exploration is required. Inflammation of a Meckel's diverticulum, with or without perforation, is rare, and its distinction from appendicitis is not usually made preoperatively.

The inguinal areas should always be explored in a child with abdominal pain to eliminate the possibility of an incarcerated inguinal or femoral hernia. In boys, testicular torsion can present with abdominal pain, while in girls pelvic inflammatory disease may mimic appendicitis. The physical findings of vaginal discharge, bilateral adnexal tenderness, and cervical motion tenderness, with less nausea and vomiting, are useful in the diagnosis of the latter. Ectopic pregnancy, pelvic endometriosis, ovarian cysts, and mittelschmerz (mid-cycle ovulation pain) must also be considered in the differential diagnosis of abdominal pain in young females.

A detailed history, taken from the parent or from the patient, is essential to determine the location, timing, and character of the pain. Progressive peritoneal irritation is suggested by pain that is exacerbated by coughing or movement; by contrast, a perforation of a walled-off abscess may cause few symptoms. The presence or absence of urinary tract symptoms and diarrhoea are important, if less specific diagnostic indicators. Timing of the onset of pain, nausea, vomiting, and anorexia may help in the differentiation between conditions requiring surgical intervention and those which will respond to more conservative treatment.

A history of relevant disease, such as sickle-cell anaemia, diabetes, haemophilia, inflammatory bowel disease, venereal disease, pancreatitis, recurrent pneumonia, pregnancy, or urinary tract infections, should be elicited. Previous abdominal surgery or trauma and any suggestion of child abuse must also be taken into consideration.

A complete physical examination, including rectal examination, must be undertaken. If results are inconclusive, examinations should be repeated every few hours, preferably by the same physician, in order to detect any progression of the illness. Immediate surgery is usually indicated in a patient with dehydration, vascular instability, blood loss, and/or unremitting or increasing acidosis despite treatment.

Complete and differential blood counts and urinalysis should be obtained. An elevated white cell count with a shift towards acute inflammation is not always a useful indicator of a need for surgical intervention. Urinalysis helps to eliminate pyelonephritis or renal or ureteral calculi as a cause of the abdominal pain, but some patients with appendicitis have red and white cells in the urine due to bladder or ureteral irritation caused by the adjacent inflammatory process. Detection of glycosuria suggests the onset of diabetes.

The radiological examinations undertaken depend upon the equipment available. Plain radiographs and barium studies are usually useful; the former allows intestinal obstruction, free intra-abdominal air and pneumonia to be identified. Ultrasound examination of the abdomen and pelvis discloses fluid collections, inflammation and abnormalities associated with the female internal genitalia, and is also useful in corroborating a diagnosis of appendicitis.

Abdominal CT scans following intravenous and/or gastrointestinal administration of contrast media should only be performed for specific indications, and are rarely needed in the evaluation of acute abdominal pain.