(Radiographics. 1999;19:299-319.)
© RSNA, 1999
Intussusception in Children: Current Concepts in Diagnosis and Enema Reduction
Gloria del-Pozo, MD1,
José C. Albillos, MD1,
Daniel Tejedor, MD2,
Rosa Calero, MD1,
Miguel Rasero, MD1,
Urbano de-la-Calle, MD1 and
Ulpiano López-Pacheco, MD1
1 Section of Pediatric Radiology, Department of Diagnostic Radiology, Hospital Universitario Infantil 12 de Octubre, Carretera de Andalucía Km 5,400, 28041 Madrid, Spain (G.d.P., J.C.A., R.C., M.R., U.d.l.C., U.L.P.)
2 Department of Diagnostic Radiology, Hospital Universitario de la Princesa, Madrid, Spain (D.T.)
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Abstract
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Intussusception cannot be reliably ruled out with clinical examination and plain radiography. However, a contrast material enema study and ultrasonography (US) allow definitive diagnosis of intussusception. The components of an intussusception produce characteristic appearances on US scans. These appearances include the multiple concentric ring sign and crescent-in-doughnut sign on axial scans and the sandwich sign and hayfork sign on longitudinal scans. Indicators of ischemia and irreducibility are trapped fluid at US and absence of blood flow at Doppler imaging. The aim of enema therapy is to reduce the greatest number of intussusceptions without producing perforation. Barium, water-soluble contrast media, water, electrolyte solutions, or air may be used with radiographic or US guidance. The differences in reduction and perforation rates between the various types of enemas are probably due more to perforations that occurred before enema therapy and the pressure exerted within the colon than to the contrast material used. The pressure within the colon is more constant with hydrostatic reduction than with air reduction; this fact may explain the lower risk of perforation with hydrostatic reduction. Radiation exposure is lower with air enema therapy than with barium enema therapy and is absent in US-guided enema therapy.
Index Terms: Children, gastrointestinal tract, 70.73 • Infants, gastrointestinal tract, 70.73 • Intestines, US, 70.1298 • Intussusception, 70.73
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INTRODUCTION
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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 6 months and 2 years of age. In this age group, intussusception is idiopathic in almost all cases. The vast majority of childhood cases of intussusception are ileocolic; that is, the ileum becomes telescoped into the colon. In the past, intussusception was a severe condition with high morbidity and mortality rates. Currently, prompt diagnosis and effective treatment lead to a favorable outcome in most cases.
In many cases, the clinical symptoms can be confusing. In fact, only 30%–68% of children with clinical findings suggestive of intussusception are shown to have this condition (1–8). Therefore, it is desirable to use diagnostic tools that are as innocuous as possible to avoid potential harm to these children, to diminish any adverse effects on the actual diseases, and to lessen the discomfort to 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 (9) is being changed to plain radiography and ultrasonography (US) at some institutions (1,2,5,7,10–18).
US is highly accurate in the diagnosis of intussusception with a sensitivity of 98%–100% and a specificity of 88%–100% (1,5,7,11,13,15,17,19,20). Furthermore, use of US may lead to an alternative diagnosis, which is not readily achieved with a contrast material enema study (1,10). Therefore, the enema could be reserved for therapeutic purposes when US is available (1,5,10,11,18). There is continuing controversy as to which type of enema is most efficacious.
In this article, the diagnosis and treatment of intussusception are reviewed. The clinical features of intussusception are described, and diagnosis with plain radiography, enema examination, and US is discussed. The various appearances of intussusception at US are presented by using a diagram that facilitates the interpretation of US scans at different levels of the intussusception. Variants of the US findings and the appearances of complicated intussusception are also presented. Treatment is discussed in general, and factors that affect the outcome of reduction are presented. The advantages and disadvantages of the various types of enema therapies are compared. Finally, a management algorithm for childhood intussusception that is based mainly on the US findings is proposed.
The information in this article is derived from our experience and a review of the literature. Our experience comprises approximately 70 cases per year of intussusception diagnosed with US during the past 10 years. In these cases, reduction of the intussusception was attempted with a barium enema (during the first 5 years), a saline solution enema under US guidance (during the last 5 years), or occasionally an air enema (17,18).
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CLINICAL FEATURES
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The classic clinical triad of acute abdominal pain (colic), currant-jelly stools or hematochezia, and a palpable abdominal mass is present in less than 50% of children with intussusception (10). The onset of nonspecific abdominal symptoms in which vomiting predominates, the absence of passage of blood via the rectum (usually in cases of less than 48 hours duration), and the inability to obtain a reliable history from these nonverbal children lead to dismissal of the diagnosis of intussusception in almost 50% of cases (21).
Furthermore, in some instances lethargy or convulsion is the predominant sign or symptom; this situation results in consideration of a neurologic disorder rather than intussusception (22). Finally, some cases in which the diagnosis is considerably delayed manifest as shock of unknown origin. To further cloud the clinical picture, other common conditions (infantile colic, gastroenteritis) or less common conditions (appendicitis, complicated Meckel diverticulum) may initially mimic intussusception. Given the uncertainty of achieving an accurate clinical diagnosis, a diagnosis based on imaging findings is required in the majority of cases.
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DIAGNOSIS WITH PLAIN RADIOGRAPHY
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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 intestine (8,9,23,24). 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 right upper quadrant projecting over the right kidney (23,25) (Fig 1). The meniscus sign consists of a crescent of gas within the colonic lumen that outlines the apex of the intussusception (the intussusceptum) (26) (Fig 2). Conversely, identification of a cecum filled with gas or feces in the normal location is the finding that allows exclusion of intussusception with the most confidence (8). The accuracy of plain radiography in diagnosis or exclusion of intussusception ranges from 40% to 90% (8,27,28).
The traditional role of plain radiography in the evaluation of children suspected to have intussusception is threefold: (a) When the clinical suspicion is low, the role of plain radiography is to allow exclusion of intussusception and diagnosis of other pathologic processes that are responsible for the patient's symptoms. (b) When the clinical suspicion is high, the role of plain radiography is to allow confirmation of intussusception. (c) If intussusception is present, the role of plain radiography is to allow exclusion of intestinal obstruction or perforation.
When vague abdominal symptoms predominate and the clinical suspicion of intussusception is low, plain radiography may lead to the diagnosis of other conditions. The discovery of a large amount of air in otherwise normal bowel loops including the cecum suggests the diagnosis of infantile colic or adynamic ileus caused by an intra- or extraabdominal infection. In these cases, no further imaging is required. Infrequently, detection of pneumonic consolidation in one of the lower lobes or of an appendicolith leads to a diagnosis other than intussusception. Owing to the low sensitivity of any imaging modality in the setting of nonspecific abdominal symptoms, plain radiography could serve as the initial screening procedure.
When there are two or more of the cardinal symptoms of intussusception, the clinical suspicion is high. In this potentially fatal disorder, a false-negative diagnosis is untenable; such a diagnosis may occur when only plain radiography is performed (8,26,27). Therefore, in cases with high clinical suspicion, use of a diagnostic tool with high sensitivity (eg, US, enema examination) is mandatory. In these cases, we and other investigators believe that it is not necessary to perform plain radiography, particularly if the symptoms are of short duration (<8 hours) (8,10,13,16).
The third purpose of plain radiography is to check for complications of prolonged intussusception: intestinal obstruction and perforation. Intestinal obstruction is readily detected on plain radiographs. The presence of intestinal obstruction does not preclude attempts at nonsurgical reduction or necessarily change the patient's treatment. If perforation is detected, primary surgery is indicated. However, to our knowledge, there are no reported cases of intussusception in which pneumoperitoneum was an initial radiographic finding, even in cases in which obvious perforation was found at surgery (8,10,29–35). Therefore, there is a low probability that perforation will be excluded with plain radiography.
For the aforementioned reasons, it does not seem advisable to routinely perform plain radiography when the clinical suspicion of intussusception is high. In this setting, we believe that it would be better to use US as the initial imaging modality. However, when the clinical findings are confusing and the symptoms are vague or of unknown origin, it would be reasonable to perform plain radiography as the initial diagnostic procedure.
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DIAGNOSIS WITH ENEMA EXAMINATION
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Barium enema examination has been the standard of reference for the diagnosis of intussusception for many years. In fact, liquid enema or air enema examination is the principal diagnostic tool at many institutions. The classic signs of intussusception at enema examination are the meniscus sign and coiled spring sign. The meniscus sign at enema examination is analogous to the meniscus sign at plain radiography and is produced by the rounded apex of the intussusceptum protruding into the column of contrast material (Fig 3a). The coiled spring sign is produced when the edematous mucosal folds of the returning limb of the intussusceptum are outlined by contrast material in the lumen of the colon (Fig 3b).
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Figure 3a. Meniscus and coiled spring signs. (a) Image from a barium enema study shows the meniscus sign in the contrast material–filled distal colon. (b) Image from a barium enema study performed after partial reduction of the intussusception shows the coiled spring sign. Contrast material outlines the facing mucosal surfaces of the intussuscipiens and the intussusceptum. (c) Image from a barium enema study performed after complete reduction of the intussusception shows barium flowing freely into the ileum.
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Figure 3b. Meniscus and coiled spring signs. (a) Image from a barium enema study shows the meniscus sign in the contrast material–filled distal colon. (b) Image from a barium enema study performed after partial reduction of the intussusception shows the coiled spring sign. Contrast material outlines the facing mucosal surfaces of the intussuscipiens and the intussusceptum. (c) Image from a barium enema study performed after complete reduction of the intussusception shows barium flowing freely into the ileum.
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Figure 3c. Meniscus and coiled spring signs. (a) Image from a barium enema study shows the meniscus sign in the contrast material–filled distal colon. (b) Image from a barium enema study performed after partial reduction of the intussusception shows the coiled spring sign. Contrast material outlines the facing mucosal surfaces of the intussuscipiens and the intussusceptum. (c) Image from a barium enema study performed after complete reduction of the intussusception shows barium flowing freely into the ileum.
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The superior performance of US in the diagnosis of intussusception, the high level of patient comfort and safety allowed by US, and the ability to arrive at alternative diagnoses with US has led us and other investigators to reserve enemas for therapeutic purposes. A potential shortcoming of this approach is that US is not available 24 hours a day at all institutions.
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DIAGNOSIS WITH US
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US has a high sensitivity for the diagnosis of intussusception (98%–100%) (1,5,7,11,13,15,17,19,20). The intussusception mass is a large structure, usually greater than 5 x 2.5 cm, that often displaces adjacent bowel loops; it is readily identified, even by inexperienced operators (5,10). The majority of intussusceptions (ie, the ileocolic type) occur in the subhepatic region. 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.
Early studies of the US appearance of intussusception reported a doughnut or pseudokidney appearance composed of a hypoechoic outer ring and a hyperechoic center. This appearance is similar to the US findings in other pathologic conditions of the gastrointestinal tract that cause thickening of the bowel wall (12,36–39). Appearances that are characteristic of intussusception have also been reported. These include the multiple concentric ring sign (40) and crescent-in-doughnut sign (17) on axial scans and the sandwich sign (1,41) and hayfork sign (42) 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 (Figs 4, 5). 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 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 (17).
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Figure 4. 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 intussusceptum: 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.
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Figure 5a. Structure of an intussusception. Axial US scans and corresponding pathologic specimens from pigs with intussusception show the doughnut sign: a hypoechoic outer ring formed by the everted limb of the intussusceptum (B) and the intussuscipiens (A) and a center that varies with the section level. C = central limb of the intussusceptum. (Reprinted, with permission, from reference 17.) (a, b) US scan (a) and pathologic specimen (b) obtained at the apex of an intussusception (section 1 in Fig 4) show a hypoechoic center, which represents the central limb of the intussusceptum with no mesentery present. Note the multilayered appearance, which is due to the demonstration of the five layers of the three bowel loops involved. (c, d) US scan (c) and pathologic specimen (d) obtained at the base of the intussusception (section 2 in Fig 4) show a hyperechoic, crescent-shaped center. This appearance occurs when the mesentery encloses the central limb of the intussusceptum (the crescent-in-doughnut sign). (e, f) US scan (e) and pathologic specimen (f) obtained at a different level of the base (section 3 in Fig 4) show an additional hypoechoic area in the hyperechoic, crescent-shaped center. This additional hypoechoic area represents a lymph node (L).
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Figure 5b. Structure of an intussusception. Axial US scans and corresponding pathologic specimens from pigs with intussusception show the doughnut sign: a hypoechoic outer ring formed by the everted limb of the intussusceptum (B) and the intussuscipiens (A) and a center that varies with the section level. C = central limb of the intussusceptum. (Reprinted, with permission, from reference 17.) (a, b) US scan (a) and pathologic specimen (b) obtained at the apex of an intussusception (section 1 in Fig 4) show a hypoechoic center, which represents the central limb of the intussusceptum with no mesentery present. Note the multilayered appearance, which is due to the demonstration of the five layers of the three bowel loops involved. (c, d) US scan (c) and pathologic specimen (d) obtained at the base of the intussusception (section 2 in Fig 4) show a hyperechoic, crescent-shaped center. This appearance occurs when the mesentery encloses the central limb of the intussusceptum (the crescent-in-doughnut sign). (e, f) US scan (e) and pathologic specimen (f) obtained at a different level of the base (section 3 in Fig 4) show an additional hypoechoic area in the hyperechoic, crescent-shaped center. This additional hypoechoic area represents a lymph node (L).
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Figure 5c. Structure of an intussusception. Axial US scans and corresponding pathologic specimens from pigs with intussusception show the doughnut sign: a hypoechoic outer ring formed by the everted limb of the intussusceptum (B) and the intussuscipiens (A) and a center that varies with the section level. C = central limb of the intussusceptum. (Reprinted, with permission, from reference 17.) (a, b) US scan (a) and pathologic specimen (b) obtained at the apex of an intussusception (section 1 in Fig 4) show a hypoechoic center, which represents the central limb of the intussusceptum with no mesentery present. Note the multilayered appearance, which is due to the demonstration of the five layers of the three bowel loops involved. (c, d) US scan (c) and pathologic specimen (d) obtained at the base of the intussusception (section 2 in Fig 4) show a hyperechoic, crescent-shaped center. This appearance occurs when the mesentery encloses the central limb of the intussusceptum (the crescent-in-doughnut sign). (e, f) US scan (e) and pathologic specimen (f) obtained at a different level of the base (section 3 in Fig 4) show an additional hypoechoic area in the hyperechoic, crescent-shaped center. This additional hypoechoic area represents a lymph node (L).
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Figure 5d. Structure of an intussusception. Axial US scans and corresponding pathologic specimens from pigs with intussusception show the doughnut sign: a hypoechoic outer ring formed by the everted limb of the intussusceptum (B) and the intussuscipiens (A) and a center that varies with the section level. C = central limb of the intussusceptum. (Reprinted, with permission, from reference 17.) (a, b) US scan (a) and pathologic specimen (b) obtained at the apex of an intussusception (section 1 in Fig 4) show a hypoechoic center, which represents the central limb of the intussusceptum with no mesentery present. Note the multilayered appearance, which is due to the demonstration of the five layers of the three bowel loops involved. (c, d) US scan (c) and pathologic specimen (d) obtained at the base of the intussusception (section 2 in Fig 4) show a hyperechoic, crescent-shaped center. This appearance occurs when the mesentery encloses the central limb of the intussusceptum (the crescent-in-doughnut sign). (e, f) US scan (e) and pathologic specimen (f) obtained at a different level of the base (section 3 in Fig 4) show an additional hypoechoic area in the hyperechoic, crescent-shaped center. This additional hypoechoic area represents a lymph node (L).
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Figure 5e. Structure of an intussusception. Axial US scans and corresponding pathologic specimens from pigs with intussusception show the doughnut sign: a hypoechoic outer ring formed by the everted limb of the intussusceptum (B) and the intussuscipiens (A) and a center that varies with the section level. C = central limb of the intussusceptum. (Reprinted, with permission, from reference 17.) (a, b) US scan (a) and pathologic specimen (b) obtained at the apex of an intussusception (section 1 in Fig 4) show a hypoechoic center, which represents the central limb of the intussusceptum with no mesentery present. Note the multilayered appearance, which is due to the demonstration of the five layers of the three bowel loops involved. (c, d) US scan (c) and pathologic specimen (d) obtained at the base of the intussusception (section 2 in Fig 4) show a hyperechoic, crescent-shaped center. This appearance occurs when the mesentery encloses the central limb of the intussusceptum (the crescent-in-doughnut sign). (e, f) US scan (e) and pathologic specimen (f) obtained at a different level of the base (section 3 in Fig 4) show an additional hypoechoic area in the hyperechoic, crescent-shaped center. This additional hypoechoic area represents a lymph node (L).
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Figure 5f. Structure of an intussusception. Axial US scans and corresponding pathologic specimens from pigs with intussusception show the doughnut sign: a hypoechoic outer ring formed by the everted limb of the intussusceptum (B) and the intussuscipiens (A) and a center that varies with the section level. C = central limb of the intussusceptum. (Reprinted, with permission, from reference 17.) (a, b) US scan (a) and pathologic specimen (b) obtained at the apex of an intussusception (section 1 in Fig 4) show a hypoechoic center, which represents the central limb of the intussusceptum with no mesentery present. Note the multilayered appearance, which is due to the demonstration of the five layers of the three bowel loops involved. (c, d) US scan (c) and pathologic specimen (d) obtained at the base of the intussusception (section 2 in Fig 4) show a hyperechoic, crescent-shaped center. This appearance occurs when the mesentery encloses the central limb of the intussusceptum (the crescent-in-doughnut sign). (e, f) US scan (e) and pathologic specimen (f) obtained at a different level of the base (section 3 in Fig 4) show an additional hypoechoic area in the hyperechoic, crescent-shaped center. This additional hypoechoic area represents a lymph node (L).
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Axial US Scans
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 4, 5). Conversely, the everted limb of the intussusceptum is thicker at the apex than at the base. Therefore, an axial US scan obtained at the apex shows a hypoechoic outer ring with a hypoechoic center (Fig 6a). In some instances, multiple concentric rings can be seen near the apex (Fig 6b). As the axial US study proceeds toward the base, the appearance changes gradually as increasing amounts of mesentery are included in the image. At the base, the amount of enclosed mesentery is maximal; the result is a hypoechoic outer ring with a hyperechoic, crescentic center (the crescent-in-doughnut sign) (Fig 6c).
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Figure 6a. Variable appearance of intussusception on axial US scans. C = central limb of the intussusceptum. (a) US scan obtained at the apex of an intussusception shows a hypoechoic outer ring separated from a hypoechoic center by a thin hyperechoic ring, which likely represents the opposed serosal surfaces of the intussusceptum (cf Figs 4 [section 1], 5a, 5b). G = gallbladder. (b) US scan obtained near the apex shows multiple concentric rings (a hypoechoic ring surrounding a hyperechoic ring, which surrounds another hypoechoic ring). The hyperechoic central ring is probably formed by the addition of the hyperechoic opposed submucosal and serosal surfaces of the intussusceptum. (c) US scan obtained at the base of an intussusception shows the central limb of the intussusceptum eccentrically surrounded by the hyperechoic mesentery (M), a situation that produces the crescent-in-doughnut sign (cf Figs 4 [section 2], 5c, 5d).
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Figure 6b. Variable appearance of intussusception on axial US scans. C = central limb of the intussusceptum. (a) US scan obtained at the apex of an intussusception shows a hypoechoic outer ring separated from a hypoechoic center by a thin hyperechoic ring, which likely represents the opposed serosal surfaces of the intussusceptum (cf Figs 4 [section 1], 5a, 5b). G = gallbladder. (b) US scan obtained near the apex shows multiple concentric rings (a hypoechoic ring surrounding a hyperechoic ring, which surrounds another hypoechoic ring). The hyperechoic central ring is probably formed by the addition of the hyperechoic opposed submucosal and serosal surfaces of the intussusceptum. (c) US scan obtained at the base of an intussusception shows the central limb of the intussusceptum eccentrically surrounded by the hyperechoic mesentery (M), a situation that produces the crescent-in-doughnut sign (cf Figs 4 [section 2], 5c, 5d).
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Figure 6c. Variable appearance of intussusception on axial US scans. C = central limb of the intussusceptum. (a) US scan obtained at the apex of an intussusception shows a hypoechoic outer ring separated from a hypoechoic center by a thin hyperechoic ring, which likely represents the opposed serosal surfaces of the intussusceptum (cf Figs 4 [section 1], 5a, 5b). G = gallbladder. (b) US scan obtained near the apex shows multiple concentric rings (a hypoechoic ring surrounding a hyperechoic ring, which surrounds another hypoechoic ring). The hyperechoic central ring is probably formed by the addition of the hyperechoic opposed submucosal and serosal surfaces of the intussusceptum. (c) US scan obtained at the base of an intussusception shows the central limb of the intussusceptum eccentrically surrounded by the hyperechoic mesentery (M), a situation that produces the crescent-in-doughnut sign (cf Figs 4 [section 2], 5c, 5d).
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Longitudinal US Scans
On longitudinal US scans, it is the arrangement of the mesentery, which may be demonstrated on one or both sides of the central limb of the intussusceptum, that causes variation in the appearance. If the middle of the intussusception is imaged along the longitudinal axis, three parallel hypoechoic bands separated by two nearly parallel hyperechoic bands are seen. The outer hypoechoic bands represent the edematous everted limb of the intussusceptum and the thin intussuscipiens; the central hypoechoic band is the central limb of the intussusceptum. The hyperechoic bands are caused by the mesentery that is dragged along with the bowel loop. This appearance is known as the sandwich sign (Fig 7a). The hayfork sign is a variant of the sandwich sign that is seen at the apex of the intussusception (42). The hayfork sign consists of three nearly parallel hypoechoic areas (the "prongs" of the hayfork), which correspond to those in the sandwich sign. The prongs are separated by two hyperechoic bands formed by the mesentery. The prongs join at the apex where the intussusceptum folds (Fig 7b). The pseudokidney sign occurs if the intussusception is curved or is imaged obliquely and the mesentery (at the point of maximal thickness) is demonstrated on only one side of the central limb of the intussusceptum (Fig 7c).
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Figure 7a. Variable appearance of intussusception on longitudinal US scans. C = central limb of the intussusceptum, M = mesentery. (a) US scan obtained in the strict longitudinal plane of an intussusception slightly away from the apex shows the sandwich sign. The outer hypoechoic bands (arrows) represent the everted limb of the intussusceptum beside the intussuscipiens. The two hyperechoic bands represent the mesentery. The central hypoechoic band represents the central limb of the intussusceptum. (b) US scan obtained at the apex of an intussusception shows the hayfork sign, which differs from the sandwich sign in that the mesentery thins as it approaches the apex. The three hypoechoic prongs of the hayfork represent the involved bowel loops separated by the hyperechoic mesentery. L = lymph node. (c) US scan shows the pseudokidney sign. The mesentery is demonstrated on one side of the central limb of the intussusceptum.
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Figure 7b. Variable appearance of intussusception on longitudinal US scans. C = central limb of the intussusceptum, M = mesentery. (a) US scan obtained in the strict longitudinal plane of an intussusception slightly away from the apex shows the sandwich sign. The outer hypoechoic bands (arrows) represent the everted limb of the intussusceptum beside the intussuscipiens. The two hyperechoic bands represent the mesentery. The central hypoechoic band represents the central limb of the intussusceptum. (b) US scan obtained at the apex of an intussusception shows the hayfork sign, which differs from the sandwich sign in that the mesentery thins as it approaches the apex. The three hypoechoic prongs of the hayfork represent the involved bowel loops separated by the hyperechoic mesentery. L = lymph node. (c) US scan shows the pseudokidney sign. The mesentery is demonstrated on one side of the central limb of the intussusceptum.
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Figure 7c. Variable appearance of intussusception on longitudinal US scans. C = central limb of the intussusceptum, M = mesentery. (a) US scan obtained in the strict longitudinal plane of an intussusception slightly away from the apex shows the sandwich sign. The outer hypoechoic bands (arrows) represent the everted limb of the intussusceptum beside the intussuscipiens. The two hyperechoic bands represent the mesentery. The central hypoechoic band represents the central limb of the intussusceptum. (b) US scan obtained at the apex of an intussusception shows the hayfork sign, which differs from the sandwich sign in that the mesentery thins as it approaches the apex. The three hypoechoic prongs of the hayfork represent the involved bowel loops separated by the hyperechoic mesentery. L = lymph node. (c) US scan shows the pseudokidney sign. The mesentery is demonstrated on one side of the central limb of the intussusceptum.
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Variants on Axial US Scans
Outer Ring.—The outer ring seen on axial US scans is usually homogeneously hypoechoic, especially at the apex of the intussusception. Occasionally, the ring is isoechoic or even hyperechoic relative to the adjacent hepatic parenchyma (Fig 8a). This variant is most often seen at the base or middle of the intussusception. We have observed that the echogenicity of the outer ring increases when the child has an attack of colicky pain. In other instances, the different layers of the bowel wall of the involved loops are demonstrated and produce a multilayered or tree ring appearance (Fig 8b). This appearance may be related to a lesser degree of vascular compromise of the intestine (12). The multilayered appearance usually occurs at the base of the intussusception and occasionally occurs at the apex of an early intussusception. Finally, hyperechoic dots are occasionally seen between the opposed mucosal surfaces of the intussuscipiens and the everted limb of the intussusceptum (Fig 8c). These dots may be caused by trapped colonic gas or mucosal ulcers.
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Figure 8a. Variant forms of the outer ring. (a) Axial US scan shows an outer ring (arrowheads) that is hyperechoic relative to the adjacent liver (L). This appearance was seen when the child had an attack of colicky pain. (b) Axial US scan shows alternating hyperechoic and hypoechoic bands (arrows) produced by the layers of the bowel wall of the intussuscipiens and the everted limb of the intussusceptum (multilayered image). (c) Axial US scan shows a band of hyperechoic dots between the thin intussuscipiens (A) and the everted limb of the intussusceptum (B). Arrowheads indicate the outer ring.
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Figure 8b. Variant forms of the outer ring. (a) Axial US scan shows an outer ring (arrowheads) that is hyperechoic relative to the adjacent liver (L). This appearance was seen when the child had an attack of colicky pain. (b) Axial US scan shows alternating hyperechoic and hypoechoic bands (arrows) produced by the layers of the bowel wall of the intussuscipiens and the everted limb of the intussusceptum (multilayered image). (c) Axial US scan shows a band of hyperechoic dots between the thin intussuscipiens (A) and the everted limb of the intussusceptum (B). Arrowheads indicate the outer ring.
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Figure 8c. Variant forms of the outer ring. (a) Axial US scan shows an outer ring (arrowheads) that is hyperechoic relative to the adjacent liver (L). This appearance was seen when the child had an attack of colicky pain. (b) Axial US scan shows alternating hyperechoic and hypoechoic bands (arrows) produced by the layers of the bowel wall of the intussuscipiens and the everted limb of the intussusceptum (multilayered image). (c) Axial US scan shows a band of hyperechoic dots between the thin intussuscipiens (A) and the everted limb of the intussusceptum (B). Arrowheads indicate the outer ring.
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Mesenteric Crescent.—The mesentery that is dragged into the intussusception with the intussusceptum is crescentic when imaged in the axial plane. The mesenteric crescent is hyperechoic but often contains hypoechoic areas (lymph nodes, the cecoappendiceal complex, vessels) (Fig 9). These variant forms are most often found at or near the base of the intussusception (17).
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Figure 9a. Variant forms of the mesenteric crescent. C = central limb of the intussusceptum. (a) Axial US scan obtained at the base of an intussusception shows the crescent-in-doughnut sign altered by inclusion of two oval mesenteric lymph nodes (L) (cf Figs 4 [section 3], 5e, 5f). (b) Axial US scan obtained at the base of an intussusception shows the crescent-in-doughnut sign altered by inclusion of the cecoappendiceal complex (arrow). (c) Axial US scan obtained at the base of an intussusception shows the crescent-in-doughnut sign altered by inclusion of the appendix (arrow) and vessels, which appear as hypoechoic dots.
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Figure 9b. Variant forms of the mesenteric crescent. C = central limb of the intussusceptum. (a) Axial US scan obtained at the base of an intussusception shows the crescent-in-doughnut sign altered by inclusion of two oval mesenteric lymph nodes (L) (cf Figs 4 [section 3], 5e, 5f). (b) Axial US scan obtained at the base of an intussusception shows the crescent-in-doughnut sign altered by inclusion of the cecoappendiceal complex (arrow). (c) Axial US scan obtained at the base of an intussusception shows the crescent-in-doughnut sign altered by inclusion of the appendix (arrow) and vessels, which appear as hypoechoic dots.
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Figure 9c. Variant forms of the mesenteric crescent. C = central limb of the intussusceptum. (a) Axial US scan obtained at the base of an intussusception shows the crescent-in-doughnut sign altered by inclusion of two oval mesenteric lymph nodes (L) (cf Figs 4 [section 3], 5e, 5f). (b) Axial US scan obtained at the base of an intussusception shows the crescent-in-doughnut sign altered by inclusion of the cecoappendiceal complex (arrow). (c) Axial US scan obtained at the base of an intussusception shows the crescent-in-doughnut sign altered by inclusion of the appendix (arrow) and vessels, which appear as hypoechoic dots.
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Central Limb of the Intussusceptum.—The central limb of the intussusceptum is collapsed in most cases. In rare instances, small amounts of fluid can be seen within the lumen of this limb. In addition, with real-time imaging, gas or fluid can be seen passing through the lumen of this limb in cases of unobstructed intussusception (Fig 10).
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Figure 10a. Variant forms of the central limb of the intussusceptum. (a) Axial US scan shows a small amount of fluid (F) within the lumen of the central limb. (b) Axial US scan shows an intensely echogenic area (arrow) with acoustic shadowing. This appearance is due to gas passing through the lumen of the central limb.
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Figure 10b. Variant forms of the central limb of the intussusceptum. (a) Axial US scan shows a small amount of fluid (F) within the lumen of the central limb. (b) Axial US scan shows an intensely echogenic area (arrow) with acoustic shadowing. This appearance is due to gas passing through the lumen of the central limb.
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Intussusceptions with Trapped Peritoneal Fluid
The presence of trapped peritoneal fluid within an intussusception correlates significantly with ischemia and irreducibility (P < .001, significant odds-likelihood ratio of 11.6–82.8) (18). Fortunately, in developed countries, this complication is seen in less than 15% of cases. Such fluid, which reflects vascular compromise of the everted limb, accumulates between the serosal layers of both limbs of the intussusceptum. The mesentery acts as a wedge and impedes the exit of fluid into the peritoneal cavity.
On axial US scans, this complication appears as the double-crescent-in-doughnut sign. In addition to the usual crescent-in-doughnut appearance, there is an anechoic crescent that represents the trapped ascites (Fig 11). In advanced stages, the everted bowel loop may become dilated probably due to ischemia and the increasing amount of trapped fluid. The dilatation occurs mainly at the antimesenteric border; the result is asymmetric distribution of the fluid (18). At US, asymmetrically distributed fluid can mimic a dilated bowel loop (eg, a closed-loop obstruction) or duplication cyst (43). Conversely, small amounts of free peritoneal fluid are seen in up to 50% of cases (Fig 12). The presence of this finding alone has not been definitely related to ischemia or an increased risk of perforation (5,44,45).
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Figure 11a. Trapped peritoneal fluid. (a) Axial US scan shows the double-crescent-in-doughnut sign, which consists of the crescent-in-doughnut sign plus an echo-free crescent due to the trapped fluid (F). (b) Longitudinal US scan at the apex of the intussusception shows the intussusceptum filled with trapped fluid.
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Figure 11b. Trapped peritoneal fluid. (a) Axial US scan shows the double-crescent-in-doughnut sign, which consists of the crescent-in-doughnut sign plus an echo-free crescent due to the trapped fluid (F). (b) Longitudinal US scan at the apex of the intussusception shows the intussusceptum filled with trapped fluid.
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Figure 12. Free peritoneal fluid. Axial US scan shows a small amount of free peritoneal fluid (F) adjacent to an intussusception that demonstrates the multiple concentric ring sign. G = gallbladder.
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Blood Flow at Doppler US
Initial reports suggested that absence of blood flow at the apex of an intussusception at Doppler US correlated with bowel necrosis and was a sign of irreducibility (15,46,47). Subsequently, a larger series demonstrated that when blood flow is not visualized at Doppler US, the rate of reduction is lower (48). However, in that series, bowel necrosis was not statistically correlated with absence of the Doppler signal. The presence of blood flow at Doppler US suggests that the intussusception would be reduced (Fig 13). Unfortunately, Doppler US is not available 24 hours a day at many institutions.
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Figure 13a. Use of Doppler US to evaluate intussusception. Doppler US scans obtained at the apex (a), middle (b), and base (c) of an intussusception clearly show blood flow within the intussusceptum (a, b) and mesentery (c). This intussusception could be reduced.
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Figure 13b. Use of Doppler US to evaluate intussusception. Doppler US scans obtained at the apex (a), middle (b), and base (c) of an intussusception clearly show blood flow within the intussusceptum (a, b) and mesentery (c). This intussusception could be reduced.
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Figure 13c. Use of Doppler US to evaluate intussusception. Doppler US scans obtained at the apex (a), middle (b), and base (c) of an intussusception clearly show blood flow within the intussusceptum (a, b) and mesentery (c). This intussusception could be reduced.
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Intussusceptions with Lead Points
Most childhood cases of intussusception are idiopathic; that is, they do not have a demonstrated anatomic abnormality that functions as a lead point except for hypertrophied lymphoid tissue. Intussusception lead points such as a Meckel diverticulum, duplication cyst, polyp, or tumor (eg, lymphoma) are uncommon in infants (<5% of cases). Intussusception lead points are more common in neonates (<30 days old), older children (>5 years old), and cases restricted to the small intestine (49). For example, intussusception of the small intestine is common in Peutz-Jeghers syndrome, in Schönlein-Henoch purpura, and after surgery.
Although lead points can be detected with a contrast enema study (50), they can easily be missed or even reduced with this technique (2,51). US allows better detection and characterization of lead points than does a contrast enema study (2,10,52,53).
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TREATMENT
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In 1836, Samuel Mitchell reported nonsurgical reduction of an intussusception. Two years later, John Gorham reported five cases treated by means of rectal insufflation of air. In 1876, Harald Hirschsprung reported reduction of an intussusception by means of a hydrostatic enema with transabdominal manipulation.
After the discovery of x rays, it became possible to monitor the reduction process in real time by using positive contrast agents. Fluoroscopically guided enema therapy was performed in the 1920s but was not scientifically tested and standardized until the studies of Ravitch and McCune (54) in the 1940s (55). Since then, contrast enema therapy has been increasingly accepted as the treatment of choice for the reduction of intussusception.
There is continuing discussion without wide agreement about which type of enema is the best for this purpose. The few randomized studies that have been performed did not show statistically significant differences in reduction and perforation rates between air and liquid enemas (3). It is likely that the reported differences in reduction and perforation rates were related not to the type of enema used but to complications that occurred before enema therapy, the technique used, the intracolonic pressures (56), and the patient selection criteria (10,22). These factors vary among the reported series. In some reports, it is difficult to ascertain many of these factors.
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FACTORS THAT AFFECT THE OUTCOME OF REDUCTION
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Complications
Although there are reports of spontaneous reduction of intussusception (57,58), chronic and recurrent intussusceptions, and rare cases of spontaneous sloughing of the gangrenous intussusceptum through the rectum (59), the usual course of an untreated intussusception is bowel obstruction followed by bowel perforation with peritonitis and septic shock. Currently, the overall perforation rate in developed countries is low (0%–3%) (22).
Perforation may already have occurred before enema therapy (30–32) or may occur during the reduction process. In the latter case, perforation may occur in normal (33,60) or ischemic (31,34,35) bowel segments or in both types (29,61). The occurrence of perforations before enema therapy depends mainly on the promptness of diagnosis and the quality of patient treatment. Therefore, the frequency of such perforations varies widely. The occurrence of perforations during the reduction process depends mainly on the pressure achieved and how long the pressure is applied and partly on the dynamics and physical properties of the contrast material used (62).
Most published studies do not differentiate between perforations established before reduction and perforations induced during reduction. It is difficult to recognize a perforation established before reduction because no cases of childhood intussusception with pneumoperitoneum as the initial finding have been reported, to our knowledge (8,10,29–35). Perforations may occur in the gangrenous ileum (the intussusceptum) or the overdistended colon (the intussuscipiens). An ileal perforation is covered by the intussuscipiens, which does not allow gas to escape into the peritoneal cavity. In a colonic perforation, the intussusceptum impedes the exit of the proximal intestinal contents. Also, because perforation occurs in cases of intussusception in which the diagnosis is delayed, the distal colonic contents will usually have been expelled by the time plain radiography is performed (30).
Technique of Reduction
The goal of any type of enema therapy is to reduce the intussusception by exerting pressure on the apex of the intussusceptum to push it from the pathologic position into the original position. The reduction and perforation rates for a specific type of enema therapy are directly proportional to the pressure applied.
Ravitch (59) found that the intracolonic pressure achieved by placing the barium enema bag 3.5 ft (105 cm) above the table did not reduce any intussusception in which the intestine was necrotic or incarcerated. Further studies found that a pressure that did not exceed 120 mm Hg for hydrostatic enemas and 108 mm Hg for air enemas did not perforate the colon in animals (60). The pressure can be controlled by measuring the height of the bag containing the fluid for a hydrostatic enema or using a manometer for an air enema. A pressure of 120 mm Hg is equivalent to a 100-cm column of barium or a 150-cm column of water or water-soluble contrast material (63). This theoretic pressure is achieved during liquid enema therapy only if the diameter of the tubing of the system is sufficiently large to easily transmit the pressure. In hydrostatic enema therapy, use of tubing and a rectal tube of large caliber may be more effective in increasing the effective intracolonic pressure than use of an increased column height (64).
Besides these theoretic considerations, it has been found empirically that intracolonic pressure reaches a plateau during hydrostatic enema therapy. This pressure is more constant than that exerted during air insufflation, which tends to produce oscillations in the intraluminal pressure with peaks that can surpass the pressure threshold. Such pressure fluctuations increase the risk of perforation (62).
There is no agreement on the number and duration of reduction attempts, the efficacy of premedication or sedation, the use of rectal tubes with inflatable retention balloons, or the use of transabdominal manipulation (65–67). This lack of agreement reflects the fact that no large studies, to our knowledge, have demonstrated a definite improvement in the reduction rate with any of these factors.
One component of the classic "rule of threes" is that the number of reduction attempts is capped at three. This rule has been discarded at some institutions, and some authors use a nearly unlimited number of attempts. These authors even use delayed attempts; that is, they repeat the reduction attempt after the patient rests for up to several hours. The aim is to improve the reduction rate (13,17,18,68–73). Use of US guidance permits an even more liberal approach to enema therapy owing to the lack of radiation exposure (16).
Use of sedation had been thought to improve the reduction rate (9). However, the reduction rate has been found to be lower when parenteral sedation is used (66). Sedation prevents the patient from performing the Valsalva maneuver during straining. The Valsalva maneuver increases the intraluminal pressure (by approximately 60 mm Hg) and decreases the colonic transmural pressure gradient. This
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Abstract
INTRODUCTION
