Acute Abdominal Pain in Children

CARIN E. REUST; AMY WILLIAMS

CARIN E. REUST, MD, MSPH, AND AMY WILLIAMS, MD, MSPH

Am Fam Physician. 2016;93(10):830-837

Author disclosure: No relevant financial affiliations.

Acute abdominal pain accounts for approximately 9% of childhood primary care office visits. Symptoms and signs that increase the likelihood of a surgical cause for pain include fever, bilious vomiting, bloody diarrhea, absent bowel sounds, voluntary guarding, rigidity, and rebound tenderness. The age of the child can help focus the differential diagnosis. In infants and toddlers, clinicians should consider congenital anomalies and other causes, including malrotation, hernias, Meckel diverticulum, or intussusception. In school-aged children, constipation and infectious causes of pain, such as gastroenteritis, colitis, respiratory infections, and urinary tract infections, are more common. In female adolescents, clinicians should consider pelvic inflammatory disease, pregnancy, ruptured ovarian cysts, or ovarian torsion. Initial laboratory tests include complete blood count, erythrocyte sedimentation rate or C-reactive protein, urinalysis, and a pregnancy test. Abdominal radiography can be used to diagnose constipation or obstruction. Ultrasonography is the initial choice in children for the diagnosis of cholecystitis, pancreatitis, ovarian cyst, ovarian or testicular torsion, pelvic inflammatory disease, pregnancy-related pathology, and appendicitis. Appendicitis is the most common cause of acute abdominal pain requiring surgery, with a peak incidence during adolescence. When the appendix is not clearly visible on ultrasonography, computed tomography or magnetic resonance imaging can be used to confirm the diagnosis.

Acute abdominal pain accounts for approximately 9% of childhood visits to primary care.¹ The initial assessment of acute abdominal pain should focus on the severity of illness and whether there is a potential surgical cause of abdominal pain. For this article, surgical cause refers to a condition that may require surgical intervention. In children presenting to the emergency department with acute abdominal pain, the incidence of appendicitis or other causes needing surgical intervention ranges from 10% to 30%^2–5; however, in general, the incidence of surgical acute abdominal pain is 2%.¹

Recommendation	Sponsoring organization
Computed tomography is not necessary in the routine evaluation of abdominal pain.	American Academy of Pediatrics
Do not do computed tomography for the evaluation of suspected appendicitis in children until after ultrasonography has been considered as an option.	American College of Surgeons

Clinical recommendation	Evidence rating	References
Urinalysis, complete blood count, pregnancy test, and erythrocyte sedimentation rate or C-reactive protein should be the initial laboratory tests in the evaluation of acute abdominal pain in children.	C	^15–18
Ultrasonography is the imaging choice for acute abdominal pain in children.	C	^23–28
Opiates may be safely used in children with acute abdominal pain without delaying or affecting the accuracy of diagnosis.	A	^34–36

History

The approach to a child with acute abdominal pain should begin with an overall assessment of the child's appearance (lethargy, eye contact, comforted by family member, interactive), food and fluid intake (decreased intake or urine output, normal intake and output), and activity level (lying still, moving about in discomfort, active). The child's age can help in narrowing potential causes of abdominal pain (Table 1^6,7 ).

All ages	Infants and toddlers (0 to 4 years)	School age (5 to 11 years)	Adolescents (12 to 18 years)
Appendicitis	Hirschsprung disease	Abdominal migraine	Ectopic pregnancy
Bowel obstruction	Infantile colic	Functional pain	Functional pain
Child abuse	Inguinal hernia	Henoch-Schönlein purpura	Inflammatory bowel disease
Constipation	Intussusception	Intussusception	Irritable bowel syndrome
Dietary indiscretions	Lactose intolerance	Lead poisoning	Menstrual-related condition
Gallbladder disease	Lead poisoning	Mononucleosis	Mononucleosis
Gastroenteritis	Malrotation of the midgut	Volvulus	Omental infarction
Hemolytic uremic syndrome	Meckel diverticulum		Other pregnancy issues
Mesenteric adenitis	Volvulus		Ovarian or testicular torsion
Pancreatitis			Pelvic inflammatory disease
Sickle cell crisis			Sexually transmitted infection
Trauma
Upper respiratory infection
Urinary tract infection

History regarding abdominal pain should include associated symptoms, previous episodes of abdominal pain, and the intensity of the pain. Important associated symptoms are bilious vomiting (bowel obstruction), bloody stool (bowel ischemia), and fever. Fever at the onset of acute illness is less likely to indicate a surgical abdomen, whereas fever after the onset of vomiting or pain is consistent with developing peritonitis. Chronic, intermittent acute abdominal pain is less likely to be related to a surgical cause than a first episode of acute pain.

Poorly localized pain that improves with movement is more likely visceral pain. Visceral pain receptors are located in the muscles and mucosa of hollow organs. Stretching or twisting of these receptors through obstruction or volvulus of organs causes pain. Visceral pain receptors in the stomach, lower esophagus, or duodenum cause epigastric pain; receptors in the small intestine cause periumbilical pain; and in the colon, lower abdominal pain. Pain that is sharp, localized, and worsens with movement has most likely originated from somatoparietal receptors found in the parietal peritoneum, muscle, and skin.

It is important to ask about other associated symptoms because a variety of etiologies cause abdominal pain in children (Table 2^1,8–14 ). Abdominal pain with cough, shortness of breath, or sore throat can be due to respiratory infection. Urinary symptoms can indicate a urinary tract infection or pyelonephritis. In pubertal girls, it is important to ask about menstrual history and sexual activity. Vaginal discharge, with or without fever, irregular spotting, or abnormal menstrual bleeding with pain can indicate pelvic inflammatory disease.

Condition	Clinical findings	Age	Comments
Abdominal migraine	Anorexia, nausea, vomiting, headache, photophobia	3 to 10 years	Boys and girls equally affected⁸
Colic	Persistent crying without apparent cause	Younger than 3 months	Nonacute abdominal examination
Constipation	Hard, infrequent stooling	All age groups	May be most common cause of abdominal pain¹
Gastroenteritis or colitis	Diarrhea, with vomiting or fever	All age groups	Campylobacter, Cryptosporidium, Escherichia coli, Salmonella, Shigella, rotavirus
Hirschsprung disease	Constipation, severe diarrhea, bowel obstruction, perforation, sepsis	Infant	Delayed passage of meconium (more than 24 hours) in about 57% of cases⁹
Inflammatory bowel disease	Bloody diarrhea	Primarily adolescents	Childhood prevalence of Crohn disease is 43 per 100,000; of ulcerative colitis, 28 per 100,000¹⁰
Omental infarction	Lower abdominal pain, vomiting, diarrhea	School-aged, overweight males¹¹	Self-limiting, diagnosed on computed tomography¹²
Ovarian cyst	Lower abdominal pain	Adolescent females	Types include hemorrhagic, ruptured, and ovulatory, and torsion of a cyst
Pneumonia	Cough, shortness of breath, fever, tachypnea	All age groups	Lower lobe pneumonia
Pyelonephritis	Flank tenderness, fever, nausea and vomiting	All age groups	Oral antibiotics for 10 to 14 days as effective as intravenous antibiotics¹³
Sexually transmitted infection	Vaginal or penile discharge, fever	Adolescent	Chlamydia trachomatis, Neisseria gonorrhoeae
Streptococcal pharyngitis	Sore throat, fever	Older than 3 years	Rapid strep test or culture
Urinary tract infection	Dysuria, urinary frequency, urinary urgency, hematuria	All age groups, primarily females and uncircumcised infants	Point prevalence in children older than one year is 7.8%¹⁴

Physical Examination

A complete examination with attention to pharyngeal erythema or exudate and focal consolidation in the lungs should be performed in children with acute abdominal pain. An abdominal examination in a sick, crying child can be difficult to perform. A family member can assist by placing his or her hands on the abdomen with the examiner's hands on top of them until the child allows the examination. Asking the child to point to the part of the abdomen that hurts the most, and then initially avoiding that area, can also facilitate the examination.

Auscultation of bowel sounds can help a clinician understand where the abdomen is painful because the child may try to block the stethoscope from that area. Absent bowel sounds can indicate ileus or peritonitis, whereas hyperactive bowel sounds may indicate obstruction. Beginning palpation just above the iliac crest in the lower quadrants of the abdomen will help identify an enlarged liver, spleen, or other abdominal mass. Gentle palpation can elicit guarding, and percussion without deep palpation can elicit rebound pain. Guarding and rebound pain can be consistent with peritonitis. Signs suggestive of the possible need for surgery for acute abdominal pain are listed in Table 3. Rectal examination may be necessary to identify a pelvic abscess or occult blood in the stool. Pelvic examination is required in pubertal girls to evaluate for pregnancy complications and sexually transmitted infections; scrotal examination is indicated in boys.

Diagnostic Evaluation

LABORATORY

Initial laboratory tests should include a complete blood count, erythrocyte sedimentation rate or C-reactive protein, a pregnancy test, if indicated, and urinalysis.^15–18 A clean void urinalysis is as accurate as a suprapubic aspiration¹⁵; the accuracy of a bag, diaper, or pad specimen is inconsistent.^19,20 A urine dipstick positive for leukocytes, esterase, and nitrite is concerning for a urinary tract infection (pooled positive likelihood ratio of 28.2 in children younger than five years [95% confidence interval, 17.3 to 46.0]).^15,21

Other tests may include liver function tests; amylase, lipase, or both for pancreatitis; sexually transmitted infection testing (Chlamydia trachomatis, Neisseria gonorrhoeae); and stool studies (Escherichia coli and Campylobacter, Cryptosporidium, Salmonella, and Shigella species), including evaluation for occult blood.

IMAGING

Radiation exposure is an important consideration before imaging in children. Radiation dose is dependent on the child's size. The cumulative effect of exposure over a lifetime of imaging needs to be assessed. Computed tomography (CT) of the abdomen and pelvis exposes a child to the equivalent of more than 100 chest radiographs. The risk of a radiation-induced solid cancer is estimated to be one per 300 to 390 CT scans of the abdomen and pelvis for girls, and one per 670 to 760 scans for boys.²² The American College of Radiology Appropriateness Criteria offer recommendations for imaging children with abdominal pain (http://www.acr.org/Quality-Safety/Appropriateness-Criteria).

Ultrasonography is relatively inexpensive and does not expose the patient to radiation. It is the first-line imaging choice for undifferentiated acute abdominal pain, unless history or physical examination identifies a specific diagnosis.^23–28 Ultrasonography can be used to evaluate for bowel thickening in inflammatory bowel disease, focal intramural bowel hematomas in Henoch-Schönlein purpura, and bowel “target” or “donut” sign in intussusception.^27,29 It is also the primary imaging choice for pyloric stenosis, cholecystitis, pancreatitis, renal calculi, ovarian cysts, ovarian torsion, and pregnancy complications.^27,28

Ultrasonography is the imaging tool of choice for evaluation of appendicitis, followed by CT or magnetic resonance imaging (MRI) for equivocal findings.^30,31 The sensitivity of ultrasonography is decreased in centers where it is used less often, when the appendix is not clearly visualized, and when there is shorter duration of pain; sensitivity is also dependent on the child's body habitus.^30,31 Ultrafast 3T magnetic resonance imaging requires only six minutes, does not require sedation, and has no radiation exposure.³²

Abdominal radiography is more likely to be diagnostic in patients with previous abdominal surgery, abnormal bowel sounds, abdominal distension, or peritoneal signs. Radiography may identify a renal or ureteric calculus, abdominal mass, ingested foreign body (including bezoars), bowel perforation with free air, and constipation.^12,27,33

CT of the abdomen may be required to diagnose complications such as necrosis from pancreatitis or abscess formation in appendicitis^27,33 and may be used for the diagnosis of omental torsion or mesenteric lymphadenitis.³³

Management of Acute Abdominal Pain

A quick workup is needed for a sick-appearing child, with attention to hydration status and pain control. For severe pain, opiates should be used and will not delay or affect the accuracy of diagnosis.^34–36 Urgent surgical consultation should not be delayed while awaiting diagnostic workup. If a child does not have an acute surgical abdomen and the diagnosis is undetermined, the examination should be repeated in 24 to 48 hours. Up to 30% of children will have a change in their diagnosis.³⁷ Figure 1 outlines the approach to the evaluation and diagnosis of acute abdominal pain.

SURGICAL CAUSES OF ACUTE ABDOMINAL PAIN

Appendicitis can occur at any age but has a peak incidence during adolescence because of lymphoid follicular hyperplasia.¹⁶ Clinical examination does not distinguish appendicitis from mesenteric lymphadenitis.³⁸ There are a variety of clinical prediction rules for appendicitis. The best validated systems are the Pediatric Appendicitis Score and the Alvarado score, which uses the mnemonic MANTRELS for the characteristics it evaluates (Table 4).³⁹ In general, prediction rules overestimate appendicitis by 30% and miss 3% to 5% of cases. A child with fever, rebound tenderness, a history of mid-abdominal pain migrating to the right lower quadrant, and an elevated white blood cell count, erythrocyte sedimentation rate, or C-reactive protein level should be evaluated for appendicitis^16,40 (eTable A).

Clinical variable	Alvarado (MANTRELS) score*	Pediatric Appendicitis Score†
Migration of pain	1	1
Anorexia	1	1
Nausea/vomiting	1	1
Tenderness in right lower quadrant	2	2
Rebound pain	1	—
Elevation in temperature (≥ 100.4°F [38.0°C])	1	1
Leukocytosis > 10,000 per mm³ (10.00 × 10⁹ per L)	2	1
Shift to the left of white blood cell count (> 75% polymorphonucleocytes)	1	1
Cough/percussion/hopping causes pain in the right lower quadrant	—	2

	LR+ (95% CI)	LR− (95% CI)
Signs and symptoms
Fever ^A1	3.4 (2.4 to 4.8)	0.32 (0.16 to 0.64)
Rebound tenderness^A2	3.0 (2.3 to 3.9)	0.28 (0.14 to 0.55)
Mid-abdominal pain migrating to right lower quadrant^A3	1.9 (1.4 to 2.5)	0.72 (0.62 to 0.85)
Laboratory tests
Erythrocyte sedimentation rate > 20 mm per hour ^A4	3.8 (1.8 to 8.1)	0.68 (0.56 to 0.81)
C-reactive protein > 10 mg per L (95.24 nmol per L)^A4	3.6 (2.1 to 6.2)	0.44 (0.33 to 0.59)
White blood cell count > 10,000 per mm³ (10.00 × 10⁹ per L)^A2	2.0 (1.3 to 2.9)	0.22 (0.17 to 0.30)
Prediction scores
Alvarado (MANTRELS) ≥ 7^A2	4.0 (3.2 to 4.9)	0.20 (0.09 to 0.41)
Pediatric Appendicitis Score ≥ 6^A5	2.4 (2.0 to 2.8)	0.27 (0.20 to 0.37)

INFANTS AND TODDLERS

In infants and toddlers, acute abdominal pain may be caused by intussusception and congenital anomalies, including Meckel diverticulum, malrotation of the midgut, and inguinal hernias. Intussusception usually occurs before two years of age.⁴¹ Infants and toddlers may present with right lower quadrant tenderness, a sausage-shaped mass in the abdomen, and red currant jelly stool caused by venous congestion of intussuscepted bowel.⁴¹ However, the classic triad of colicky abdominal pain, vomiting, and bloody stool is found in less than 50% of cases.^29,41 In children, 90% of cases of intussusception are idiopathic, with 10% of cases resulting from a lead point or sticky spot in the colon.⁴¹ Air or contrast enema can be diagnostic and therapeutic for intussusception.

Symptomatic Meckel diverticulum can present with gastrointestinal bleeding, diverticulitis, bowel obstruction, peritonitis, intussusception, or volvulus. One-half of such cases occur in children younger than four years.^12,41 Malrotation of the midgut leading to volvulus causes bilious vomiting, pain, diarrhea, and bloody stools in more advanced cases. Incarcerated inguinal hernias present with a tender groin mass.

ADOLESCENTS

In adolescents, acute abdominal pain may result from a gonad- or pregnancy-related pathology. Ovarian torsion presents with intermittent, nonradiating unilateral lower abdominal pain with an enlarged adnexa on ultrasonography or CT.⁴² Testicular torsion commonly presents with a tender scrotum and enlarged testis in adolescents, but boys may present with a complaint of hip or abdominal pain with nausea or vomiting.

Ectopic pregnancy and early pregnancy loss must be considered in adolescent girls. Both conditions may present with vaginal bleeding, cramping pain, and abdominal tenderness. An intrauterine pregnancy should be visualized with transvaginal ultrasonography when the beta human chorionic gonadotropin level is 1,500 to 2,000 mIU per mL (1,500 to 2,000 IU per L).⁴³ Early pregnancy loss may be seen as an empty gestational sac or gestational sac without fetal heart activity on transvaginal ultrasonography.⁴⁴ Repeat ultrasonography and serial beta human chorionic gonadotropin testing may be required to confirm pregnancy loss.

Data Sources: We searched Essential Evidence Plus, Ovid Medline and Medline In-Process, Scopus, DynaMed, ACP Physicians Information and Education Resource, Clinical Evidence, and the National Guideline Clearinghouse. Keywords and truncated text words were included in the following search string: (abdominal pain or abdomen, acute or acute abdom$) AND (preschool child or child or adolescent) AND (diagnostic techniques and procedures or diagnostic test, routine or diagnos$ or differential or clinical laboratory techniques or physical exam$ or early diagnosis) AND (sensitive$ or specificity or diagnostic errors or likelihood or reproducibility of results or area under curve or probabili$ or accuracy$ or false positive$ or false negative$ or false rate$ or receiver operat$ or roc or observer variation$ or predictive value$). Retrieval included meta-analyses, systematic reviews, randomized controlled trials, clinical trials, guidelines, and diagnostic studies. Search date: November 26, 2014.

Loening-Baucke V, Swidsinski A. Constipation as cause of acute abdominal pain in children. J Pediatr. 2007;151(6):666-669.

Farion KJ, Michalowski W, Rubin S, Wilk S, Correll R, Gaboury I. Prospective evaluation of the MET-AP system providing triage plans for acute pediatric abdominal pain. Int J Med Inform. 2008;77(3):208-218.

O'Shea JS, Bishop ME, Alario AJ, Cooper JM. Diagnosing appendicitis in children with acute abdominal pain. Pediatr Emerg Care. 1988;4(3):172-176.

Reynolds SL, Jaffe DM. Diagnosing abdominal pain in a pediatric emergency department. Pediatr Emerg Care. 1992;8(3):126-128.

Tsalkidis A, Gardikis S, Cassimos D, et al. Acute abdomen in children due to extra-abdominal causes. Pediatr Int. 2008;50(3):315-318.

Leung AK, Sigalet DL. Acute abdominal pain in children. Am Fam Physician. 2003;67(11):2321-2326.

Montgomery DF, Hormann MD. Acute abdominal pain: a challenge for the practitioner. J Pediatr Health Care. 1998;12(3):157-159.

Carson L, Lewis D, Tsou M, et al. Abdominal migraine: an under-diagnosed cause of recurrent abdominal pain in children. Headache. 2011;51(5):707-712.

Singh SJ, Croaker GD, Manglick P, et al. Hirschsprung's disease: the Australian Paediatric Surveillance Unit's experience. Pediatr Surg Int. 2003;19(4):247-250.

Kappelman MD, Rifas-Shiman SL, Kleinman K, et al. The prevalence and geographic distribution of Crohn's disease and ulcerative colitis in the United States. Clin Gastroenterol Hepatol. 2007;5(12):1424-1429.

Gosain A, Blakely M, Boulden T, et al. Omental infarction: preoperative diagnosis and laparoscopic management in children. J Laparoendosc Adv Surg Tech A. 2010;20(9):777-780.

Saito JM. Beyond appendicitis: evaluation and surgical treatment of pediatric acute abdominal pain. Curr Opin Pediatr. 2012;24(3):357-364.

Strohmeier Y, Hodson EM, Willis NS, Webster AC, Craig JC. Antibiotics for acute pyelonephritis in children. Cochrane Database Syst Rev. 2014;7:CD003772.

Shaikh N, Morone NE, Bost JE, Farrell MH. Prevalence of urinary tract infection in childhood: a meta-analysis. Pediatr Infect Dis J. 2008;27(4):302-308.

Whiting P, Westwood M, Watt I, Cooper J, Kleijnen J. Rapid tests and urine sampling techniques for the diagnosis of urinary tract infection (UTI) in children under five years: a systematic review. BMC Pediatr. 2005;5(1):4.

Bundy DG, Byerley JS, Liles EA, Perrin EM, Katznelson J, Rice HE. Does this child have appendicitis?. JAMA. 2007;298(4):438-451.

Shaikh N, Morone NE, Lopez J, et al. Does this child have a urinary tract infection?. JAMA. 2007;298(24):2895-2904.

Kwan KY, Nager AL. Diagnosing pediatric appendicitis: usefulness of laboratory markers. Am J Emerg Med. 2010;28(9):1009-1015.

Etoubleau C, Reveret M, Brouet D, et al. Moving from bag to catheter for urine collection in non-toilet-trained children suspected of having urinary tract infection: a paired comparison of urine cultures. J Pediatr. 2009;154(6):803-806.

McGillivray D, Mok E, Mulrooney E, Kramer MS. A head-to-head comparison: “clean-void” bag versus catheter urinalysis in the diagnosis of urinary tract infection in young children. J Pediatr. 2005;147(4):451-456.

White B. Diagnosis and treatment of urinary tract infections in children. Am Fam Physician. 2011;83(4):409-415.

Miglioretti DL, Johnson E, Williams A, et al. The use of computed tomography in pediatrics and the associated radiation exposure and estimated cancer risk. JAMA Pediatr. 2013;167(8):700-707.

Yarmish GM, Smith MP, Rosen MP, et al. American College of Radiology. ACR appropriateness criteria. Right upper quadrant pain. http://www.acr.org/~/media/ACR/Documents/AppCriteria/Diagnostic/RightUpperQuadrantPain.pdf. Accessed January 23, 2016.

Bhosale PR, Javitt MC, Atri M, et al. ACR appropriateness criteria. Acute pelvic pain in the reproductive age group. [Published ahead of print November 19, 2015]. Ultrasound Q. http://journals.lww.com/ultrasound-quarterly/Abstract/publishahead/ACR_Appropriateness_Criteria_R__Acute_Pelvic_Pain.99880.aspx. Accessed January 23, 2016.

Karmazyn B, Coley BD, Binkovitz LA, et al. American College of Radiology. ACR appropriateness criteria. Urinary tract infection—child. http://www.acr.org/~/media/ACR/Documents/AppCriteria/Diagnostic/UrinaryTractInfectionChild.pdf. Accessed January 23, 2016.

Smith MP, Katz DS, Rosen MP, et al. American College of Radiology. ACR appropriateness criteria. Right lower quadrant pain—suspected appendicitis. http://www.acr.org/~/media/7425a3e08975451eab571a316db4ca1b.pdf. Accessed January 23, 2016.

Hayes R. Abdominal pain: general imaging strategies. Eur Radiol. 2004;14(suppl 4):L123-L137.

Shah S. An update on common gastrointestinal emergencies. Emerg Med Clin North Am. 2013;31(3):775-793.

Mendez D, Caviness AC, Ma L, Macias CC. The diagnostic accuracy of an abdominal radiograph with signs and symptoms of intussusception. Am J Emerg Med. 2012;30(3):426-431.

Mittal MK, Dayan PS, Macias CG, et al.; Pediatric Emergency Medicine Collaborative Research Committee of the American Academy of Pediatrics. Performance of ultrasound in the diagnosis of appendicitis in children in a multicenter cohort. Acad Emerg Med. 2013;20(7):697-702.

Bachur RG, Dayan PS, Bajaj L, et al.; Pediatric Emergency Medicine Collaborative Research Committee of the American Academy of Pediatrics. The effect of abdominal pain duration on the accuracy of diagnostic imaging for pediatric appendicitis. Ann Emerg Med. 2012;60(5):582-590.e3.

Johnson AK, Filippi CG, Andrews T, et al. Ultrafast 3-T MRI in the evaluation of children with acute lower abdominal pain for the detection of appendicitis. AJR Am J Roentgenol. 2012;198(6):1424-1430.

Carty HM. Paediatric emergencies: non-traumatic abdominal emergencies. Eur Radiol. 2002;12(12):2835-2848.

Green R, Bulloch B, Kabani A, Hancock BJ, Tenenbein M. Early analgesia for children with acute abdominal pain. Pediatrics. 2005;116(4):978-983.

Ranji SR, Goldman LE, Simel DL, Shojania KG. Do opiates affect the clinical evaluation of patients with acute abdominal pain?. JAMA. 2006;296(14):1764-1774.

Sharwood LN, Babl FE. The efficacy and effect of opioid analgesia in undifferentiated abdominal pain in children: a review of four studies. Paediatr Anaesth. 2009;19(5):445-451.

Toorenvliet BR, Bakker RF, Flu HC, Merkus JW, Hamming JF, Breslau PJ. Standard outpatient re-evaluation for patients not admitted to the hospital after emergency department evaluation for acute abdominal pain. World J Surg. 2010;34(3):480-486.

Toorenvliet B, Vellekoop A, Bakker R, et al. Clinical differentiation between acute appendicitis and acute mesenteric lymphadenitis in children. Eur J Pediatr Surg. 2011;21(2):120-123.

Ebell MH, Shinholser J. What are the most clinically useful cutoffs for the Alvarado and Pediatric Appendicitis Scores? A systematic review. Ann Emerg Med. 2014;64(4):365-372.e2.

Kharbanda AB, Taylor GA, Fishman SJ, Bachur RG. A clinical decision rule to identify children at low risk for appendicitis. Pediatrics. 2005;116(3):709-716.

Pepper VK, Stanfill AB, Pearl RH. Diagnosis and management of pediatric appendicitis, intussusception, and Meckel diverticulum. Surg Clin North Am. 2012;92(3):505-526.

Appelbaum H, Abraham C, Choi-Rosen J, Ackerman M. Key clinical predictors in the early diagnosis of adnexal torsion in children. J Pediatr Adolesc Gynecol. 2013;26(3):167-170.

American College of Obstetricians and Gynecologists. ACOG Practice Bulletin no. 94. Medical management of ectopic pregnancy. Obstet Gynecol. 2008;111(6):1479-1485.

Committee on Practice Bulletins—Gynecology. American College of Obstetricians and Gynecologists Practice Bulletin no. 150. Early pregnancy loss. Obstet Gynecol. 2015;125(5):1258-1267.