Epidemiology

Abdominal pain is a common complaint in children. Up to 25% of children will experience discomfort severe enough to interfere with activity, and annually, one in every seven children in the United States will visit a physician because of abdominal complaints, yet most will have no organic cause identified. Between 2% and 4% of all pediatric outpatient visits are related to abdominal complaints.^1–3 Discerning the presence of serious underlying disease can be challenging. This chapter describes several of the most significant pathologic abdominal conditions in pediatric patients.

Abdominal Masses

Obstructive uropathy and renal cysts are the most likely causes of abdominal distention in infancy. Abdominal tumors are slow growing and usually recognized incidentally (e.g., when a parent or physician feels an abdominal mass). The two most common malignancies are Wilms tumor and neuroblastoma. The majority of affected children are younger than 5 years. Wilms tumor arises from the renal parenchyma and in most cases is asymptomatic. Neuroblastoma develops from the adrenal gland or along the sympathetic chain and may thus be manifested as either a midline or flank mass. It is an aggressive malignancy and has often metastasized at diagnosis. Ultrasonography and computed tomography (CT) are useful for investigation of abdominal lesions. A pediatric surgeon and oncologist should be consulted early for management of abdominal tumors.

Gastrointestinal Bleeding

As a general rule, gastrointestinal (GI) bleeding is not usually as severe in children as in adults. In particular, the vast majority of cases of neonatal GI bleeding are benign. The first step in evaluation is to confirm that the suspicious material found in the stool or diaper is actually blood by performing a guaiac filter test for occult blood. Children routinely consume both foods (watermelon) and liquids (antibiotics such as cefdinir, fruit punch, and other juices) that turn the stool red, which may falsely lead both parents and health care workers to believe that GI blood loss is occurring. The benign pink or orange urate crystals in the urine of some neonates and young children are sometimes mistaken for blood when seen in diapers. Urinary tract infections and urethral prolapse may also result in deposition of blood in the diaper that could be confused with GI blood.

Upper GI bleeding produces dark brown, black, or simply heme-positive stool. However, because of the fast transit time in neonates, some upper GI bleeding may be bright red. The most common cause is swallowed maternal blood, acquired either during delivery or as a result of breastfeeding from irritated or cracked nipples.

Esophageal varices are rare in children. In contrast to adults, in whom primary hepatic disease is the leading cause, the most likely cause of varices in children is splanchnic and portal vein obstruction. Varices may develop secondary to umbilical vein catheterization, dehydration, sepsis, or omphalitis. Less common causes are hepatic parenchymal conditions such as biliary cirrhosis secondary to biliary atresia, cystic fibrosis, α₁-antitrypsin deficiency, and hepatitis. Early onset of inflammatory bowel disease occurs in the teenage years and is uncommon in younger children.

Perirectal skin breakdown and external rectal fissures both produce blood-streaked stool and are easily identifiable on physical examination. Sitz baths and stool softeners are useful in treating rectal fissures.

Emergency department (ED) management of GI bleeding is directed at fluid and blood resuscitation.

Meckel Diverticulum

A Meckel diverticulum is the most common omphalomesenteric remnant. The most frequently observed finding is painless rectal bleeding, which occurs as a result of ulceration of the diverticulum or neighboring mucosa by the ectopic tissue. The ectopic tissue is gastric in origin in more than 80% of cases, but it may be pancreatic as well. Symptoms usually occur within the first 2 years of life, and in the majority of affected individuals it is diagnosed by 20 years of age (Box 22.1). A Meckel diverticulum can act as a lead point in intussusception. The diagnostic study of choice is a radiolabeled bleeding study called a Meckel scan. Definitive therapy is surgical excision.

Intussusception

Intussusception occurs when one loop of intestine invaginates into another. Intussusception of the mesentery can also occur and result in edema and vascular congestion. It is the most common cause of intestinal obstruction in children younger than 6 years. The ileocolic region is most often involved. Intussusception is usually manifested in children 6 to 18 months old, with a peak occurrence at 10 to 12 months. The vast majority of cases in children younger than 3 years are idiopathic. One etiologic theory is that inflammation of Peyer patches within the intestine acts as a lead point for the intussusception. In children older than 5 years, a true lead point is found more than 75% of the time. Lead points include polyps, lymphoma, Meckel diverticulum, surgical adhesions, and mucosal inflammation secondary to vasculitis.

Intussusception is often preceded by a viral illness, and the patient may have a low-grade fever at the time of evaluation. Symptoms consist of vomiting and episodic, crampy abdominal pain. Initially, children return to baseline between episodes, but as the condition persists, they may become lethargic. Screaming episodes lasting up to 10 to 15 minutes with hip and knee flexion are routine. The episodes increase in frequency and duration over time, with subsequent shortening of asymptomatic intervals.

The classic triad of symptoms—vomiting, abdominal pain, and “currant jelly” stools—is seen in less than one third of patients. However, more than 75% have two of these findings. Early on, stools test guaiac negative. If bowel ischemia ensues, frank blood mixed with mucus gives the stool a currant jelly appearance.

Some children have only lethargy, which can delay the diagnosis. The most commonly confused entity is constipation because of the similar pattern of colicky abdominal pain. These two conditions can easily be differentiated with a plain abdominal radiograph.

The history is the best guide to the diagnosis of intussusception. On abdominal palpation the right lower quadrant may be empty because the cecum has rotated out of its standard position. The actual intussusception may be palpated as a sausage-shaped mass in the right upper quadrant. Normal physical findings should not dissuade the examiner from proceeding with investigation because most children appear normal between episodes. No laboratory studies are available to confirm the diagnosis, and guaiac test–positive stool is a late finding. Abdominal radiographic findings are most often normal, but a mass may be seen in the right upper quadrant.

Intussusception can be reliably diagnosed with ultrasound.⁴ Enemas are both diagnostic and therapeutic. Intussusceptions that cannot be reduced by enema must be reduced surgically. Up to 10% of cases recur, most often within 24 hours. After reduction, the child must be admitted to the hospital for a 24-hour observation period.

Children with a history and physical findings suspicious for intussusception must be evaluated quickly because the passage of time increases both the edema and the difficulty of achieving reduction. A pediatric surgeon should be contacted before the child undergoes attempted enema reduction in case of failure or perforation. Ileoileal intussusceptions may be difficult to visualize and reduce via enema unless there is significant reflux of contrast material. Such intussusceptions are associated with Henoch-Schönlein purpura (HSP), in which the vasculitis acts as a lead point.⁵

Henoch-Schönlein Purpura

HSP is a vasculitis that predominantly affects the capillaries and small vessels. It occurs most commonly in school-age children, with the classic triad consisting of abdominal pain, purpura, and arthritis. Elevations of immunoglobulin A (IgA) are detectable in the blood, along with immune complex deposition in the skin and glomeruli. There is no known etiology, but HSP has often been found to occur after upper respiratory infections. Recurrences are seen in up to 50% of cases.

Abdominal pain occurs in half the patients and is most frequently colicky in nature. Intussusception should be strongly considered in children with guaiac test–positive or frankly bloody stools accompanied by severe pain. The subtype of intussusception associated with HSP is often ileoileal, which is difficult to visualize and reduce with a contrast enema. CT is the imaging modality of choice for ileoileal intussusception associated with HSP, and reduction must often be achieved surgically.

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