Intussusception

Intussusception is one of the most common causes of acute abdomen in infancy. Intussusception occurs when a portion of the digestive tract becomes telescoped into the adjacent bowel segment. This condition usually occurs in children between 3 months and 2 years of age. In almost all cases intussusceptions are idiopathic, that is, they do not have a demonstrated anatomic abnormality that functions as a lead point except for hypertrophied lymphoid tissue. The vast majority of childhood cases of intussusception are ileocolic. In the past, intussusception was a severe condition with high morbidity and mortality rates. Today, prompt diagnosis and effective non-surgical reduction lead to a favorable outcome in most cases.

1.2.1.1 Diagnosis

The classic clinical presentation is characterized by acute (colic) abdominal pain with drawing up of the legs, currant-jelly stools or hematochezia, and a palpable abdominal mass. These findings, however, are present in less than 50% of children with intussusception (DaneMan and Alton 1996). The onset of nonspecific abdominal symptoms in which vomitus predominates, the absence of passage of blood via the rectum (usually in cases of less than 48 h duration), and the inability to obtain a reliable clinical history may lead to dismissal of the diagnosis of intussusception in some cases. In some instances lethargy or convulsion is the predominant sign or symptom, this situation resulting in consideration of a neurologic disorder. Some cases in which the diagnosis is considerably delayed manifest as shock of unknown origin due to the progression of the disease to mechanical obstruction causing vascular comprise and bowel infarction. On the other hand, less than 50% of children with clinical findings suggestive of intussusception are shown to have this condition (del Pozo et al. 1999). Therefore, it is desirable to use diagnostic tools that are as innocuous as possible to avoid potential harm to these children, diminish any adverse effects on the actual diseases, and to lessen the discomfort of the children who are not shown to have intussusception. To this end, the traditional diagnostic approach to childhood intussusception of plain radiography and enema examination has been changed to plain radiography and US at most institutions, keeping the enema for therapeutic purposes.

Many plain radiographic signs of intussusception have been described. The most common is a soft-tissue mass, which is most often seen in the right upper quadrant effacing the adjacent hepatic contour. Other signs include reduced air in the small intestine or a gasless abdomen, air in a displaced appendix, and obstruction of the small bowel (Gilsanz 1984; Sargent et al. 1994). The most specific plain radiographic findings are the "target sign" and "meniscus sign". The "target sign" consists of a soft-tissue mass that contains concentric circular or nearly circular areas of lucency, which are due to the mesenteric fat of the intussusceptum. The mass is most often seen in the upper right quadrant projecting over the right kidney (Ratoliffe et al. 1992) (Fig. 1.44). The "meniscus sign" consists of a crescent of gas within the colonic lumen that outlines the apex of the intussusception (the intussusceptum) (Fig. 1.45). Conversely, identification of a cecum filled with air or feces in the normal location is the finding that allows exclusion of intussusception with the most confidence (Sargent et al. 1994). However, plain abdominal radiography is normal in 40%-50% (Sargent et al. 1994; Meradji et al. 1994). Therefore, several authors do not recommend plain radiography if there is high clinical suspicion of intussusception (Versohelden et al. 1992), especially when the symptoms are of short duration. In such cases, US should be the initial imaging procedure (Woo et al. 1992; Daneman and Alton 1996; Riebel et al. 1993).

US has a high sensitivity for the diagnosis of intussusception (98%-100%) (Praoros et al. 1987;

Riebel et al. 1993; Wang and Liu 1988). Because deep penetration of the ultrasound beam is not necessary in small children, a high-resolution transducer (5-10 MHz) can be used to improve the definition of the image. The majority of intussusceptions (i.e. the ileocolic type) occur in the

Meniscus Sign Intussusception
Fig. 1.45. Meniscus sign. Plain radiograph shows the meniscus sign: a rounded soft-tissue mass (the intussusceptum) protruding into the gas-filled transverse colon (arrow) [From del Pozo (1999)]
Upper Abdomen Purtrugion

Fig. 1.44a,b. Target sign. a,b Two different patients. Plain radiographs show a round soft-tissue mass in the right upper quadrant (arrows). The masses contain a ring-like area of lucency [From del Pozo (1999)]

Fig. 1.44a,b. Target sign. a,b Two different patients. Plain radiographs show a round soft-tissue mass in the right upper quadrant (arrows). The masses contain a ring-like area of lucency [From del Pozo (1999)]

b a subhepatic region. The intussusception mass is a large structure, usually greater than 5 x 2.5 cm, that often displaces adjacent bowel loops. Early studies of the US appearance of intussusception reported a doughnut or pseudokidney appearance composed of a hypoechoic outer ring and a hyperechoic center (Swischuck et al. 1985). This appearance is similar to the US findings in other pathologic conditions of the gastrointestinal tract that cause thickening of the bowel wall. Appearances that are characteristic of intussusception include the "multiple concentric ring" sign (Holt and Samuel 1978) and "crescent-in-doughnut" sign (del Pozo et al. 1996a) on axial scans, and the "sandwich" sign (Pracros et al. 1987; MoNtali et al. 1983) and "hayfork" sign (Alessi and SalerNo 1985) on longitudinal scans. In US of intussusception, the terms axial and longitudinal refer to the axis of the intussusception.

An intussusception is a complex structure (Fig. 1.46). The intussuscipiens (the receiving loop) contains the folded intussusceptum (the donor loop), which has two components: the entering limb and returning limb. The attached mesentery is

MS i

Fig. 1.46. Structure of an intussusception. Diagram shows a longitudinal view and three axial views of an intussusception; three bowel loops and the mesentery can be seen. The intussuscipiens (A) contains the two limbs of the intussus-ceptum: the everted returning limb (B), which is edematous, and the central entering limb (C), which is located at the center of the intussusception with the accompanying mesentery (M). The mesentery contains some lymph nodes (L). MS, contacting mucosal surfaces of the intussuscipiens and everted limb; S, contacting serosal surfaces of the everted limb and central limb. [From del Pozo (1999)]

dragged between the entering and returning limbs. The thickest component of the intussusceptum is the everted returning limb, which, together with the thin intussuscipiens, forms the hypoechoic outer ring seen on axial scans. The center of the intussusception contains the central or entering limb, which is of normal thickness and is eccentrically surrounded by the hyperechoic mesentery.

On axial US scans, intussusception has a variable appearance, which is primarily due to the amount of enclosed mesentery. Enclosed mesentery is absent at the apex of the intussusception and progressively increases toward the base (Figs. 1.46 and 1.47). Conversely, the everted limb of the intussuscep-tum is thicker at the apex than at the base. Therefore, an axial US scan obtained at the apex shows

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