Evaluation of pediatric abdominal pain can prove a diagnostic challenge. Children may be limited in their ability to give an accurate history. Parents or guardians may also have difficulty interpreting the complaints of small children. In many cases, the causes are benign with few long-term sequelae. However, some require rapid diagnosis and treatment in order to prevent significant morbidity or mortality. Consideration of the child's age helps narrow the differential diagnoses to include pediatric-specific conditions. 
The clinician should determine early on whether the abdominal pain is acute or chronic in nature, as this will help indicate the urgency of treatment. Acute abdominal pain is usually a single episode that typically lasts from hours to days. The pain may vary in severity over time and is often localized and described as sharp and/or stabbing in nature. Conversely, chronic abdominal pain typically lasts days to weeks to months, and is usually dull, diffuse, and poorly localized. There may be pain-free intervals of variable duration, and when it recurs the pain may vary in intensity. In addition, the history should cover the following:
Onset, frequency, duration, and time of day that the abdominal pain occurs: gastroenteritis lasting >10 days suggests parasitic or noninfectious cause; the onset and progression of mesenteric adenitis may be insidious or dramatic; recurrent, self-resolving episodes of pain are characteristic of biliary colic, whereas pain that is constant over 24 hours or more is suggestive of acute cholecystitis; sudden-onset flank pain can indicate nephrolithiasis or pyelonephritis
Whether the pain is localized or diffuse: RLQ pain suggests appendicitis; Evidence A epigastric pain suggests peptic ulcer disease; diffuse pain may indicate perforation or peritonitis
Whether the pain radiates or migrates between areas of the abdomen: abdominal pain radiating to the back is suggestive of cholecystitis or pancreatitis
Any factors that make the pain better or worse, such as movement, food, or medication: in cholelithiasis/cholecystitis pain often occurs after eating (particularly fatty foods); epigastric pain due to peptic ulcer disease is usually related to eating meals
The character of the pain: pain associated with peptic ulcer disease is dull rather than burning in nature; sharp or stabbing pain is typical of appendicitis
The presence and severity of any associated symptoms such as: fever, nausea, vomiting, anorexia, diarrhea (gastroenteritis); fatigue, jaundice (viral hepatitis); lethargy, headache, cough, shortness of breath (pneumonia or empyema); pain elsewhere (e.g., sudden onset testicular pain suggests testicular torsion), blood in stool (ulcerative colitis, necrotizing enterocolitis, dysentery), and blood or bile in vomitus (small bowel obstruction)
The presence of genitourinary symptoms: dysuria, frequency of micturition, and hematuria suggest a UTI; vaginal discharge is suggestive of pelvic inflammatory disease (PID); current menstruation may be indicative of dysmenorrhea
History of trauma: whether blunt or penetrating, accidental or nonaccidental
Travel history: travel to a developing country increases risk of viral hepatitis infection and infectious gastroenteritis
Past medical history focusing on previous operations, medication use, immunizations, allergies, and current comorbidities: patients with sickle cell disease or cystic fibrosis are at higher risk of developing gallstones; patients with spina bifida, mental retardation, and cerebral palsy are prone to constipation; splenic infarction may be a consequence of sickle cell disease; recent or current upper respiratory tract infection is suggestive of mesenteric adenitis or pulmonary cause 
Stooling patterns: infrequent bowel action or fecal incontinence is suggestive of constipation
Dietary history: helpful when evaluating constipation; new or unusual food intake may support the diagnosis of gastroenteritis
Family history: positive FHx is a risk factor for inflammatory bowel disease as well as nephrolithiasis
Social and psychiatric history including family dynamics: may help determine if pain is functional or due to organic cause; psychological factors (e.g., depression, abuse, attention deficit disorder, oppositional disorder), weaning, toilet training, start of schooling, or other causes of stress may play a role in constipation
Sexual history in females of reproductive age: adolescents may avoid answering sensitive questions regarding sexual history and drug use truthfully in the presence of parents or guardians; therefore, it may be appropriate to conduct some parts of the history with the adolescent alone.
This should be performed in a comfortable and nonthreatening manner. Children may need to be distracted by parents or guardians in order to obtain an accurate exam. In younger children, localization of the abdominal pain may be difficult. Consideration of vital signs should be based on age-appropriate normal values. Because pediatric abdominal pain may originate from other areas of the body (e.g., genitals or lungs), a comprehensive physical exam is necessary, including performing a rectal exam and checking stool for occult blood (guaiac test). Pelvic exam is not routinely performed; history is usually a guide and digital exam should be reserved for adolescents who are sexually active.
A diagnosis of constipation should be considered when an otherwise well child has mild abdominal tenderness, and stool in the rectum on digital rectal exam. In severe cases abdominal distension may be present with a palpable fecal mass per abdomen or rectum. The presence of an anal fissure and/or hemorrhoids (rare in children; may be mistaken for skin tags from Crohn disease [CD]), imperforate anus or anal stenosis (particularly in a neonate or infant) may provide further diagnostic clues. Children with spina bifida, mental retardation, and cerebral palsy are also prone to constipation, and features of these conditions may be obvious on exam (e.g., sacral dimples or pits and/or tags/tufts indicative of abnormality of spinal cord). Psychological assessment may explain why symptoms are intractable in the absence of a severe physiologic predisposition.
Patients presenting with central abdominal pain, with or without guarding and rigidity, that settles in the RLQ should arouse suspicion of appendicitis. Evidence A Acute mesenteric adenitis often resembles acute appendicitis; however, pain in the abdomen is usually diffuse with tenderness not localized to the RLQ. Guarding may be present but rigidity is usually absent. Generalized lymphadenopathy is common and signs of an upper respiratory tract infection may be present (e.g., hyperemic pharynx or oropharynx suggesting pharyngitis).
Patients with gastroenteritis usually exhibit diffuse abdominal pain without evidence of peritonitis (no guarding or rebound tenderness). Abdominal distension and hyperactive bowel sounds are a common finding. It is important to determine whether signs of volume depletion are present (tachycardia, hypotension, dry mucous membranes, poor capillary refill, sunken fontanelle in infants). The presence of mucus in the stool suggests a bacterial or parasitic etiology. Blood in the stool is indicative of dysentery or hemolytic uremic syndrome.
Intussusception should be suspected in an infant between 3 and 12 months of age presenting with colicky abdominal pain, flexing of the legs, fever, lethargy, and vomiting. Henoch-Schonlein purpura (HSP) may be the initiating factor in an older child (usually <11 years of age), and therefore signs of HSP should be sought (rash of palpable purpura, blood in the stools).
The presence of abdominal distension and tenderness associated with decreased or absent bowel sounds is strongly suggestive of large bowel obstruction. The presence of bilious vomiting with (partial obstruction) or without (complete obstruction) the passage of stool/flatus suggests small bowel obstruction.
The clinical presentation of peptic ulcer disease in children >6 years of age mimics adults and should be suspected in a child presenting with epigastric pain with or without acute or chronic blood loss (pallor on exam).
Ulcerative colitis often presents with bloody diarrhea, whereas this is an unusual presentation in CD. Both conditions cause cramping abdominal pain, anorexia, and weight loss when they present late in the course of the disease. Extraintestinal manifestations of inflammatory bowel disease may be evident (e.g., iritis, arthritis, sacroiliitis, erythema nodosum, pyoderma gangrenosum). Depending on the intestinal location of CD, it may mimic other disease processes such as acute appendicitis.
Fever may be the only presenting sign of a UTI, especially in the younger age group, and UTI should therefore be a top differential in children between 2 months and 2 years of age with fever. Abdominal or flank pain is a more common finding in older children. High fever is suggestive of pyelonephritis; it is estimated that in children presenting with suspected UTI, up to two-thirds have concurrent pyelonephritis.  
Cholecystitis is often associated with fever. Jaundice is rare with cholelithiasis or acute cholecystitis and, if present, suggests an obstruction of the common bile duct. Tenderness in the RUQ is a classic sign of gallbladder disease, as is Murphy sign (cessation of inspiration during concurrent deep RUQ palpation).
Patients with biliary dyskinesia usually present in a similar fashion to those with cholelithiasis and cholecystitis and may have RUQ tenderness on palpation. Physical exam findings can be equivocal.
Patients with splenic infarction typically present with fever as well as left-sided abdominal pain; occasionally patients may be asymptomatic. Pain may also be reported in the left side of the chest or the left shoulder. Those with a splenic cyst are either asymptomatic or present with dull left-sided abdominal pain in the absence of fever. 
Tenderness in the epigastric or upper abdominal quadrants of the abdomen is typical of pancreatitis. With more severe disease systemic signs such as fever, tachycardia, and hypotension are usually present. Patients may lie with their knees and hips flexed and avoid moving. It is important to note that, in younger patients with pancreatitis (<3 years of age), abdominal tenderness may not be the main finding; these patients may demonstrate increased irritability and abdominal distension. With hemorrhagic pancreatitis, discoloration may be noted around the umbilical area (Cullen sign) or in the flanks (Grey-Turner sign) due to blood tracking along defined fascial planes.
Abdominal tenderness and/or renal angle tenderness associated with gross or macroscopic hematuria usually indicate underlying nephrolithiasis.
The presence of cyanosis, tachypnea, decreased breath sounds on auscultation, dullness on percussion (indicates consolidation), and abdominal tenderness and distension without guarding or rebound, should arouse suspicion of a pulmonary cause such as pneumonia or empyema.
Testicular torsion is likely in any male child with abdominal tenderness plus loss of the cremasteric reflex, diffuse testicular tenderness, elevated testes, and a horizontal rather than vertical position of the testes on exam. Torsion of a testicular appendage may be confused with testicular torsion; however, it does not compromise the viability of the testes and frequently requires only supportive care. Pain may develop more gradually (over days to weeks) and frequently is pinpoint (superior pole of testes). In addition, systemic symptoms such as nausea and vomiting are not usually present.
The presence on physical exam of jaundice associated with abdominal tenderness, hepatomegaly (splenomegaly may also be present), and lymphadenopathy, particularly in a child of school age, should arouse suspicion of viral hepatitis (commonly hepatitis A).
Abdominal trauma should be considered when abdominal pain is out or proportion to physical exam findings. Signs of accidental (e.g., seatbelt mark suggesting a motor vehicle accident) and nonaccidental injury (particularly if history is suspicious) should be sought (e.g., cigarette burns, subdural hemorrhages in an infant/young toddler). Blood at the urethral meatus, or hematuria, may suggest urinary tract or kidney injury.
If clinical findings are minimal and the child appears well, a diagnosis of functional abdominal pain should be considered. Diagnostic criteria for functional abdominal pain are symptom based, not physical exam or laboratory based. 
Infants and toddlers
In a neonate, the triad of abdominal distension, delayed passage of meconium (not occurring in the first 36 hours of life), and vomiting is highly suggestive of Hirschsprung disease. Necrotizing enterocolotis should be considered in a premature neonate weighing less than 1500 g. Early signs may include inability to tolerate feeds, abdominal distension and tenderness, blood in the stool, and abdominal wall erythema. In severe cases, systemic signs of sepsis may be present. A neonate presenting with bilious vomiting, with (partial obstruction) or without (complete obstruction) the passage of meconium, is highly suggestive of small bowel obstruction. Causes such as meconium ileus, intestinal atresia, and midgut volvulus should be excluded with further investigations.
Meckel diverticulum should be considered in a child <2 years old with abdominal tenderness (Meckel diverticulitis); hematochezia, typically dark red, maroon, or "red currant jelly" stools (indicates intestinal bleeding as they contain heterotopic gastric tissue); or signs of obstruction such as nausea, vomiting, and obstipation (intussusception, volvulus, or herniation can result).
Ectopic pregnancy and miscarriage should be suspected in any female of reproductive age presenting with lower abdominal pain, amenorrhea, and vaginal bleeding. Pelvic exam may reveal a mass, eliciting cervical motion tenderness if hemoperitoneum is present; tubal rupture can cause hemodynamic instability. Clinical features of a ruptured ovarian cyst usually occur prior to the expected time of ovulation and may mimic ectopic pregnancy. Pain arises from local peritonitis secondary to hemorrhage.    Peritonism may be present in lower abdomen and pelvis; adnexal size is unremarkable due to collapsed cyst. The presence of a tender pelvic mass associated with nausea and vomiting may suggest ovarian torsion. In addition, in patients old enough to undergo pelvic exam, cervical motion tenderness may be elicited; typically no vaginal discharge is present, but there may be some mild to moderate vaginal bleeding.
Physical findings of PID vary widely and may include lower abdominal tenderness, adnexal tenderness, and cervical motion tenderness. Fever and cervical or vaginal discharge may also be present. If suspected in a young child, signs of sexual abuse should be sought. Patients with PID may also present with RUQ pain resulting from inflammation of the liver capsule or diaphragm, referred to as Fitz-Hugh-Curtis syndrome. This is secondary to an ascending infection. Referred pain to the right shoulder may result from irritation of the diaphragm.    Primary dysmenorrhea should be considered if lower abdominal tenderness is associated with current menstruation.
Challenges in the clinical evaluation of abdominal pain in the pediatric patient mean laboratory and imaging studies can play an important role.
Initial tests should include a CBC (useful in evaluating infection and inflammation) and complete chemistry panel (electrolyte disturbances associated with GI causes are common). Urinalysis is essential to exclude underlying UTI or hematuria (associated with nephrolithiasis, UTI, hemolytic uremic syndrome, urinary tract or kidney injury) and should be performed in children of all ages presenting with abdominal pain. For females of reproductive age a urine pregnancy test and/or serum beta-hCG is necessary to exclude miscarriage and ectopic pregnancy. Type and screen is essential when a ruptured ectopic pregnancy is suspected, as the rhesus status of the mother determines the need for RhoGAM administration. LFTs are helpful baseline investigations, when considering a hepatobiliary or pancreatic cause (e.g., viral hepatitis, cholecystitis, pancreatitis). Serum amylase and lipase is indicated if pancreatitis is suspected. Although nonspecific, ESR and CRP may suggest underlying infection or inflammation. Furthermore, these inflammatory markers correlate closely with disease activity in cases of inflammatory bowel disease.
Stool microscopy and culture may be helpful in determining an infectious etiology of gastroenteritis. Risk factors and features of the clinical presentation help guide the choice of tests for specific pathogens. The 2017 Infectious Disease Society of America (IDSA) guideline on infectious diarrhea recommends that when there is fever or bloody diarrhea, investigations for enteropathogens for which antimicrobial agents may confer clinical benefit (including Salmonella enterica subspecies, Shigella , and Campylobacter ) should be done.  Blood cultures are indicated when sepsis is a concern. The IDSA guideline also recommends blood cultures: in children with infectious diarrhea who are <3 months of age or who are immunocompromised; when enteric fever is suspected (including travel to enteric fever-endemic area, or contact with travelers from enteric fever-endemic areas who have a febrile illness of unknown etiology); when there are systemic manifestations of infection; and with high-risk conditions such as hemolytic anemia.  Urine culture is necessary if urinalysis is suggestive of a UTI. Sputum culture is usually reserved for those patients with suspected pneumonia. Aspiration of frank pus on thoracentesis is diagnostic of empyema. In cases of patients with suspected peptic ulcer disease, Helicobacter pylori breath test or stool antigen test may be helpful. Serologic markers (perinuclear antineutrophil cytoplasmic antibody and antisaccharomyces cerevisiae antibody) may be particularly useful for differentiating between CD and ulcerative colitis in the pediatric population. Polymorphonuclear leukocytes (PMNs) seen on wet mount of vaginal secretions confirms vaginal infection in cases of PID. In all patients with PID, it is important to screen for other STDs. Therefore, HIV serology, syphilis serology, hepatitis studies, and genetic probe or culture of vaginal secretions for Neisseria gonorrhoeae and Chlamydia trachomatis are indicated. In patients with suspected exposure to or symptoms of hepatitis A, B, C, D, and E, the following laboratory tests are warranted: hepatitis A antibody IgM, hepatitis B serology or viral load, hepatitis C serology or viral load, hepatitis D and E serologies. A coagulation profile, including PT and INR, is usually necessary in cases of suspected viral hepatitis to measure liver synthetic function.
Imaging studies are guided by history and physical exam findings. Plain abdominal x-rays are often nonspecific but may suggest the presence of an obstruction; fecal impaction can be detected on x-ray, as well as duodenal atresia. In addition, if sufficiently radio-opaque, it may be possible to identify gallstones or urinary stones on a plain abdominal film. This is often the initial test, as it can be performed quickly. Supine and upright films are usually requested. Free air under the diaphragm suggests perforation and requires immediate surgical evaluation. Chest x-ray should be ordered if perforation is suspected or a respiratory cause such as pneumonia or empyema is likely.
Ultrasound scans avoid radiation exposure and are typically better tolerated than other imaging modalities such as CT scan. An experienced pediatric radiologist may be able to utilize ultrasound in all regions of the body (abdomen, chest, testicles). Ultrasound scans are considered particularly useful in evaluating pain in the RUQ (i.e., gallbladder disease), and lower abdominal pain (pelvic pain) in females. Color Doppler may be helpful in determining ovarian blood flow in cases of suspected ovarian torsion. Testicular ultrasound (using power Doppler ultrasound and/or gray-scale ultrasound) should be able to diagnose testicular torsion and provide information on the vascular integrity of the testis. Ultrasound of the urinary tract (including kidneys) is of benefit when wanting to exclude anatomic abnormalities (e.g., when UTI is present) or nephrolithiasis and associated complications such as hydronephrosis.
Focused abdominal sonography for trauma (FAST) may be useful in children with blunt abdominal trauma who are hemodynamically unstable.  The presence of large amounts of free fluid indicates a need for immediate operative intervention. FAST in hemodynamically stable patients has a less certain impact, as a negative scan does not preclude injury. A large multi-institutional study at pediatric trauma centers demonstrated poor FAST sensitivity (28.6%) in normotensive patients.  Though specificity was high (91.1%), results of FAST rarely changed management. A randomized trial comparing FAST with standard care in hemodynamically stable children and adolescents with blunt torso trauma also found no significant difference in the proportion of abdominal CT scans, missed intra-abdominal injuries, length of stay in the emergency department, and median hospital costs.  Abdominal CT scan with intravenous contrast is the diagnostic test of choice for the identification of solid organ injuries, especially to the liver, kidney, and/or spleen. Oral contrast is usually not necessary when scanning a patient for trauma.
Ultrasound is recommended as the first imaging test for suspected appendicitis.  CT with contrast may be appropriate after nondiagnostic ultrasound; however, radiation exposure with its risk of malignancy should be considered. MRI avoids ionizing radiation and has similar or better sensitivity and specificity than CT, though availability and longer scan times may limit its utility. 
In general, for investigation of abdominal pain in children, CT scan of the abdomen and pelvis, with or without contrast, may provide a high yield of information, but radiation exposure should be considered.  Sedation or general anesthesia may be required in some children.
GI contrast studies (upper-GI or barium enema studies) are routinely used in place of CT scans, especially in infants. In evaluation of intestinal obstruction, clinical suspicion should direct which contrast study should be performed first and will be most informative.
Endoscopy (esophagogastroduodenoscopy or colonoscopy) with biopsy may be required to evaluate mucosa-based diseases, such as peptic ulcer disease and inflammatory bowel disease. Rectal biopsy and anorectal manometry help confirm the diagnosis of Hirschsprung disease. These procedures may be particularly challenging when performed in a newborn.
Diagnosis of biliary dyskinesia is confirmed by hepatobiliary iminodiacetic acid (HIDA) scan with an ejection fraction <35%. It is important to note that the cutoff of <35% is not universally accepted; some consider an ejection fraction <15% to be more predictive of success of surgical treatment (i.e., cholecystectomy).  HIDA scan is also considered a useful adjunct in the diagnosis of cholecystitis. Technetium-99m pertechnetate scan is considered the most useful method to diagnose a suspected Meckel diverticulum; this scan identifies ectopic gastric mucosa as tracer is taken up by parietal cells.
The American Academy of Pediatrics (AAP) recommend that a voiding cystourethrogram is indicated in children between 2 and 24 months of age following an initial UTI if renal and bladder ultrasonography reveals hydronephrosis, scarring, or other findings that would suggest either high-grade vesicoureteral reflux or obstructive uropathy, as well as in other atypical or complex clinical circumstances. Further evaluation should be conducted if there is a recurrence of febrile UTI.  Other guidelines have slightly different recommendations.  
Full skeletal x-rays (skeletal survey) identify previous skeletal injuries and should be obtained if there is a high suspicion of nonaccidental trauma. This should only be performed to provide adjunctive diagnoses to support an initial injury and suspicion of abuse.
Diagnostic laparoscopy may be necessary to confirm diagnosis of PID as it allows direct visualization of the gynecologic and abdominal structures.
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