Chapter 383. Acute Abdominal Pain

Abdominal pain is among the most common complaints in children, accounting for approximately 10% of all children evaluated in emergency units. Abdominal pain can be acute and sudden in onset or chronic with continual or intermittent symptoms. Most episodes of pain are benign and resolve with minimal or no intervention.1 One recent study showed that only 23% of all children evaluated in an emergency department required surgical intervention, most often for appendicitis.1 Differentiating abdominal pain that requires prompt surgical intervention from pain due to nonsurgical conditions is often challenging, especially in the infant and toddler. The evaluation and management of abdominal pain varies depending on the severity and character of the pain, associated symptoms, and age and sex of the child. The difficulties in diagnosis can be reduced by considering the most likely diagnosis based on the child’s age, the presence of associated symptoms, and the physical examination.

Pathophysiology

The sensation of abdominal pain is transmitted to the central nervous system via somatic and visceral afferent fibers. The visceral afferent system innervates the visceral peritoneum and its structures. Visceral pain localizes poorly, but pain originating from the stomach, duodenum, and pancreas generally localizes to the epigastrium; pain originating from the small bowel, colon, and spleen localizes to the periumbilical region; and pain originating from the rectosigmoid and bladder localizes to the hypogastrium. Renal or ureteral pain is usually localized to the flank. Gallbladder pain is often poorly localized but may localize to the right upper quadrant. Pain originating from the parietal peritoneum from inflammation or abdominal wall pain is well localized. Referred pain results from the convergence of visceral and somatic pain pathways in the spinal cord, so pain originating in abdominal viscera may be perceived as originating at a distant, well-isolated somatic location. For example, diaphragmatic irritation secondary to pancreatitis, a bleeding spleen, cholecystitis, or liver abscess may be interpreted as pain arising in the vicinity of the lower neck and shoulders because the diaphragm and shoulder pain pathways converge in the spinothalamic tracts at C4. Similarly, gallbladder inflammation may be sensed in the right infrascapular region, pancreatic pain may be sensed in the posterior flank, a migrating ureteral stone may be felt progressing toward the ipsilateral groin, and rectal and gynecologic discomfort may be sensed in the vicinity of the sacrum. Conversely, pain originating in somatic locations, such as the right pleural surface with pneumonia, may be perceived as originating in the lower abdomen because pain afferents from both regions converge at T10-11.

Clinical Features and Differential Diagnosis

Pain of sudden onset is likely associated with colic, perforations, and acute ischemia (eg, torsions, volvulus). Slower onset of pain generally is associated with inflammatory conditions such as appendicitis, pancreatitis, and cholecystitis. Colic results from spasms of a hollow muscular viscus (eg, biliary tree, pancreatic duct, gastrointestinal tract, urinary system, uterus and fallopian tubes) and is usually secondary to an obstructive process. In general, children with visceral pain due to colic have episodic severe cramping with intervals when the pain is absent or markedly reduced. During the painful episodes, the patient is usually writhing, agitated, restless, and often pale and diaphoretic. Inflammatory pain secondary to peritoneal irritation usually results in a quiet, motionless, ill-appearing patient in whom pain is exacerbated with movement.

The approach to differential diagnosis in a child with abdominal pain is shown in Figure 383-1. The differential diagnosis of acute abdominal pain varies depending on the age of the patient and the location and duration of the pain (new onset of pain or exacerbation of existing pain). Causes of acute abdominal pain in children are shown in Table 383-1. Abdominal pain in the newborn manifests with incessant crying, drawing up of the legs, and other nonspecific symptoms such as feeding refusal. Diagnoses such as incarcerated hernia, bowel obstruction, urinary tract infection, and volvulus must be considered.2 In all ages, the presence of red flags such as bilious vomiting and abdominal distension suggesting bowel obstruction; signs of impending shock such as hypotension, confusion, and diaphoresis; hematemesis or melena; or features of peritonitis demand immediate evaluation for the specific presenting symptom or sign. Fever is associated with gastrointestinal infections, bowel ischemia, and perforation but may also occur in many of the other disorders associated with abdominal pain. A history of possible trauma or abuse may be associated with visceral injury and/or pancreatitis. A history of colicky episodes with lethargy suggests possible intussusception. Previous intra-abdominal surgery suggests a possibility of bowel obstruction due to adhesions, intussusception, or intra-abdominal hernia. Other medical conditions, such as a history of hemolytic disease, cystic fibrosis, or inflammatory bowel disease, may also alter the likelihood of various diagnoses. A history of heartburn or epigastric tenderness may suggest acid-peptic disease. Associated symptoms and signs such as dysuria (urinary tract infection), polyuria (diabetes mellitus), hematuria (renal stone), purpura (Henoch-Schönlein purpura), or diarrhea (gastroenteritis, colitis) may narrow the differential diagnosis. In females, the gynecologic history is important. A history of sexual activity may suggest pelvic inflammatory disease or pregnancy. Midcycle pain of short duration may suggest mittelschmerz. Extra-abdominal causes of perceived abdominal pain include rectus muscle hematoma, testicular torsion, herpes zoster, diabetic ketoacidosis, porphyria, sickle cell disease, myocardial infarction, pneumonia, pulmonary embolus, radiculitis, spider and scorpion stings, and poisoning (heavy metals, methanol). Pain out of proportion to the physical findings can suggest ischemic pain, which is uncommon in pediatric patients, or may be behavioral and associated with attention seeking.

Diagnostic Evaluation

Following a careful history to determine likely causes of abdominal pain, a careful physical examination guides the urgency and extent of evaluation. In the ill-appearing child with abnormal vital signs, a surgical or infectious etiology that requires prompt intervention is likely. Jaundice suggests liver disease or hemolysis.

The abdomen should be observed, auscultated, and palpated to evaluate distension, localized tenderness, masses, and peritonitis. After the patient identifies the area of most pain, the examiner should gently palpate less painful sites, then the most tender area. Findings of rebound tenderness or abdominal rigidity indicate that peritoneal inflammation is likely. Gentle percussion may elicit rebound tenderness, while deep palpation is required to evaluate for a mass. Findings of a Rovsing sign (pressure in the left lower quadrant eliciting right lower quadrant pain), ileo-psoas sign (pain on passive extension of the right hip), or obturator sign (pain on rotation of the right flexed hip) in a cooperative child may increase the suspicion of appendicitis. A positive Murphy sign (pain with deep inspiration when palpating below the right costal margin) suggests acute cholecystitis, and a Grey Turner sign (bluish discoloration of the flank) suggests internal hemorrhage. Findings of purpura or arthritis suggest Henoch-Schönlein purpura.3 An experienced examiner often uses distraction and/or palpation with a stethoscope to allow a more accurate evaluation of the severity of pain because some children may exaggerate pain symptoms. A rectal examination may be useful to evaluate for masses, tenderness, or melena. Pelvic examination may be required in the sexually active or near menarcheal female to evaluate for evidence of pelvic inflammation or imperforate hymen. Other sources of pain, such as pneumonia and musculoskeletal disorders, should be considered. The examiner must avoid frightening the patient; in selected patients, repeat examination following sedation may be useful. In the very obese patient, well-localized inflammation and peritoneal signs may be masked due to overlying layers of fat.

Initial laboratory studies for the patient with acute abdominal pain include a complete blood count, urinalysis, and pregnancy test (for postmenarcheal females).4 Leukocytosis suggests the presence of inflammation associated with bowel perforation or ischemia, but it may be only mildly elevated in some children with surgical causes of pain. Plain films of the abdomen may be helpful to identify intestinal obstruction or perforation of a viscus, and chest radiographs may rule out pneumonia. However, abdominal/pelvic computed tomography (CT) or abdominal ultrasound, because of their improved diagnostic sensitivity and specificity, have largely supplanted these tests for causes of abdominal pain, including appendicitis in both children and adults.5-7 Ultrasound is also used routinely for the diagnosis of appendicitis,8,9 ovarian cyst, ovarian torsion, ectopic pregnancy and periappendiceal inflammation in some emergency departments.10 CT appears to be more accurate than ultrasound, but accuracy may depend on the skill of the operator, the suspected diagnosis, and the patient’s age. The comparative efficacy, risks, and benefits of abdominal CT versus ultrasound may be mitigated with new ultralow-dose CT methodologies.10

Treatment

Treatment depends on the underlying cause of the abdominal pain. If the cause remains unclear following a directed evaluation, then repeated examinations and/or hospital admission may be required to determine whether the pain will resolve spontaneously or a if more extensive evaluation is indicated. Traditionally, administration of analgesics such as morphine was avoided because of concern that it might obscure the underlying diagnosis, resulting in delayed surgical intervention and adverse outcomes. Several studies indicate that the administration of analgesia in both children and adults with acute abdominal pain did not alter diagnostic acumen or outcome.11-15 Administration of morphine (0.1 mg/kg intravenously, up to 10 mg) or related agents is now recommended while the diagnostic evaluation progresses. However, a more recent study that evaluated this approach found that although there was no difference in the outcomes of children treated with analgesics there was also no difference in pain relief following these doses of analgesia.16