13.2 Intussusception & the Surgical Abdomen

Intussusception

Intussusception occurs when a proximal segment of bowel (the intussusceptum) telescopes into an adjacent distal segment (the intussuscipiens), dragging its mesentery with it. Impaired venous return leads to bowel wall edema and mucosal bleeding, and if reduction is delayed, arterial compromise, ischemia, and perforation follow. It is the most common cause of intestinal obstruction in infants and toddlers, with peak incidence between 3 months and 3 years of age (most cases cluster between 6 and 18 months). The ileocolic type, in which the terminal ileum invaginates through the ileocecal valve into the colon, accounts for the large majority of cases.

Most pediatric intussusception is idiopathic, thought to follow lymphoid (Peyer's patch) hyperplasia after a preceding viral illness — adenovirus is classically implicated — which acts as a soft lead point. A true pathologic lead point, such as a Meckel diverticulum, intestinal polyp, duplication cyst, or lymphoma, is more likely in children outside the typical age range (under 3 months or over 5 years) and in cases that recur after reduction; a bowel-wall hematoma from Henoch-Schonlein purpura is another recognized lead point in older children. This age-based reasoning is a favorite exam discriminator: a 6-month-old with idiopathic intussusception needs enema reduction, while a 6-year-old with intussusception needs a search for a mass lesion.

Recognition and Diagnosis

The classic triad — intermittent, severe colicky abdominal pain, currant-jelly stool (blood and mucus reflecting mucosal sloughing and venous congestion), and a palpable sausage-shaped mass, usually in the right upper quadrant — is present together in only a minority of cases, so its absence does not exclude the diagnosis. More consistently, infants draw their legs up during pain episodes, appear well or even lethargic between episodes (a striking and testable pattern), and may vomit as obstruction progresses. Lethargy out of proportion to exam findings is itself a recognized presenting sign in young infants and should raise suspicion even without abdominal pain reported.

Abdominal ultrasound is the diagnostic test of choice: a target sign (doughnut sign) on transverse view and a pseudokidney sign on longitudinal view reflect the layered, telescoped bowel wall. Ultrasound also identifies a pathologic lead point and free fluid suggesting ischemia.

Treatment

When there is no evidence of peritonitis, perforation, or shock, an air enema (or hydrostatic saline/contrast enema) performed under fluoroscopic or ultrasound guidance is both diagnostic and therapeutic, successfully reducing roughly 80-90% of cases. Perforation is an absolute contraindication to enema reduction; peritonitis or hemodynamic instability mandates surgery instead. After successful non-operative reduction, recurrence risk is roughly 10%, concentrated in the first 24-48 hours, so infants are typically observed with advancing feeds before discharge. Failed enema reduction, perforation, or a pathologic lead point requires operative reduction with resection of non-viable bowel or the lead point itself.

Other Causes of the Pediatric Surgical Abdomen

Malrotation with Midgut Volvulus

Malrotation is incomplete rotation and fixation of the midgut during embryonic development, leaving the small bowel mesentery attached by a narrow pedicle instead of its normal broad base. This narrow pedicle can twist — midgut volvulus — cutting off superior mesenteric artery flow and threatening infarction of the entire midgut within hours. The classic presentation is a previously well neonate (most present in the first month of life) with sudden-onset bilious vomiting; as emphasized in Section 13.1, bilious vomiting is a surgical emergency until malrotation and volvulus are excluded. The abdomen may look deceptively benign early on, so a normal exam should never delay workup. The diagnostic study of choice is an upper GI contrast series, showing a corkscrew-shaped duodenum or a duodenojejunal junction that fails to cross the midline to the left of the spine; frank peritonitis or hemodynamic instability bypasses imaging for immediate laparotomy. Treatment is the Ladd procedure (division of Ladd's bands, widening of the mesenteric pedicle, and prophylactic appendectomy), performed emergently once volvulus is diagnosed or strongly suspected clinically.

Appendicitis in Young Children

Acute appendicitis is less common in infants and young children than in older children and adults, but when it occurs it is more dangerous: perforation rates in children under 5 years reach roughly 50-80% at presentation, compared with roughly 20% in adolescents. Several factors drive this: young children cannot reliably localize or describe pain, the classic migratory periumbilical-to-right-lower-quadrant pattern is often absent, presentation is nonspecific (fussiness, poor feeding, vomiting, low-grade fever) and easily mistaken for gastroenteritis, and the immature, poorly developed omentum cannot wall off a perforation as effectively — so disease progresses to diffuse peritonitis faster. Because history and exam are less reliable in this age group, ultrasound is typically the first-line imaging study to avoid radiation, with CT reserved for equivocal cases. The exam-relevant lesson: a young child with vague abdominal complaints and systemic illness deserves a lower threshold for surgical evaluation than an adolescent with the same complaint.

Incarcerated Inguinal Hernia

An incarcerated inguinal hernia occurs when herniated bowel (or ovary in a female infant) cannot be reduced through the internal inguinal ring, risking bowel ischemia and obstruction. Presentation includes a firm, tender groin or labial/scrotal mass that may be erythematous, irritability, vomiting, and progressive abdominal distention if bowel is obstructed. A reducible hernia softens when gently compressed and disappears when the infant is calm; an incarcerated hernia remains fixed and tender. This is a surgical emergency requiring urgent referral for manual reduction if feasible, or operative repair if reduction fails or signs of strangulation appear — a common exam stem pairs a crying infant with a non-reducible groin mass and bilious or persistent vomiting.