The Role Of Sonography In Intussusception
Albert H Lam MD, FRACR, DDU
Associate Professor, Department of Medical Imaging, Royal Alexandra Hospital for Children, University of Sydney

Introduction
Intestinal intussusception occurs when a segment of bowel (intussusceptum) passes onwards inside the adjacent distal bowel (intussuscipiens). The condition is the most common acute abdominal disorder of early childhood and occurs in about 3.5 of 1,000 admissions to a children's hospital (1). It is rare under three months and over three years of age, with a peak incidence of between five and nine months. It occurs more frequently in boys with a ratio of 5:1. The most common type of intussusception is ileocolic, followed by ileoileocolic, ileoileal and colocolic. Over 95 % occur without a leadpoint, classified as primary or idiopathic type. However, this type usually results from abnormal peristalsis centred on the thickened Peyer's patches secondary to a recent viral infection in the winter months, or change of bowel flora during weaning. About 5 to 10 % are classified as secondary type when there is a demonstrable leadpoint. Possible leadpoints include an inverted Meckel's diverticulum, intestinal polyp or lymphoma, enteric duplication, intramural haematoma or an inverted appendiceal stump after appendicectomy. The secondary intussusception usually occurs in infants older than 3 years of age. An untreated intussusception can be fatal. The prolonged obstruction causes bowel oedema and compression of the invaginated mesenteric vessels. This leads to intestinal ischaemia, perforation, peritonitis, sepsis, dehydration and shock. The complications usually occur after 24 hours of obstruction and early diagnosis and treatment is vital. The classical clinical triad of abdominal pain, red currant jelly stool and palpable abdominal mass is present in less than 50% of children with intussusception and as many as 20% may present pain free. This makes clinical diagnosis difficult, particularly when over 70% of cases are under one year of age. The clinician, therefore, often has to rely on imaging procedures to diagnose or exclude intussusception promptly and accurately.

Conclusion
Appropriate use of sonography in children with known or suspected intussusception obviates the necessity for a diagnostic enema, facilitates the diagnosis of leadpoint or other intra-abdominal lesions and helps confirm complete reduction in difficult cases. Furthermore, it may show spontaneous reduction and recurrence. In our institution, we use sonography for diagnosis and air or barium enema for reduction, reserving the abdominal radiograph for children with clinical or sonographic evidence of peritonitis with a suspected perforation. Direct surgical intervention is indicated when there is gut necrosis demonstrated with sonography and colour Doppler.