M

Fig. 1.47a,b. Correlation of sonographic and pathologic findings in intussusceptions in pigs. a Axial US scan; b corresponding pathologic specimen. Axial sections at the base show a doughnut sign with a peripheral hypoechoic ring (formed by the everted limb of the intussusceptum and the intussuscipiens) and a hyperechoic crescent shaped center due to the mesentery enclosing the hypoechoic central limb of intussusceptum (crescent-in-doughnut sign). A, intussuscipiens; B, everted limb of intussusceptum; C, central limb of intussusceptum; M, mesentery [From dei Pozo (1996a)

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)]

a hypoechoic outer ring with a hypoechoic center. In some instances, multiple concentric rings can be seen near the apex. 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 cres-cent-in-doughnut sign) (Fig. 1.48).

On longitudinal US scans, it is the arrangement of the mesentery 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. 1.49a). The hayfork sign is a variant of the sandwich sign that is seen at the apex of the intussusception. 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. 1.49b). The hyperechoic mesentery often contains hypoechoic areas that correspond to lymph nodes, the cecoap-pendiceal complex, or vessels (dEl Pozo et al. 1999) (Fig. 1.50).

The presence of trapped peritoneal fluid within an intussusception correlates significantly with ischemia and irreducibility (del Pozo et al. 1996b). 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 (Fig. 1.51). 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. 1.51). Conversely, small amounts of free peritoneal fluid are seen in up to 50% of cases. The presence of this finding alone has not been definitely related to ischemia or an increased risk of perforation (Swischuk and Stansberry 1991). The absence of blood flow within the intussusception on Doppler US correlates with irreducibility but not definitely with bowel necrosis (Kong et al. 1997). The presence of blood flow at Doppler US suggests that the intussusception would be reduced (Fig. 1.52).

Most childhood cases of intussusception are idiopathic. Intussusception lead points such as a Meckel diverticulum, duplication cyst, polyp, or tumor (e.g. lymphoma) are uncommon in infants (< 5% of cases). Intussusception lead points are more common in neonates, older children (> 5 years old), and cases restricted to the small intestine. For example, intussusception of the small intestine is common in Peutz-Jeghers syndrome, Schönlein-Henoch purpura, and after surgery. US allows

Fig. 1.48a,b. The crescent-in-doughnut sign. Axial US scans obtained at the middle (apex proximal regions) (a) and at the base (b) of an intussusception, show the central limb of the intussusceptum (C) eccentrically surrounded by the hyperechoic mesentery (M), a situation that produces the crescent-in-doughnut sign [From del Pozo (1999)]

Fig. 1.48a,b. The crescent-in-doughnut sign. Axial US scans obtained at the middle (apex proximal regions) (a) and at the base (b) of an intussusception, show the central limb of the intussusceptum (C) eccentrically surrounded by the hyperechoic mesentery (M), a situation that produces the crescent-in-doughnut sign [From del Pozo (1999)]

Fig. 1.49a,b. Intussusception on longitudinal US scans. Variable appearance of intussusception on longitudinal US scans depending on which side of the central limb of the intussusceptum the mesentery is imaged. It may be depicted at one side (pseudo-kidney) or at both sides (sandwich). 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 shows the pseudokidney sign. The mesentery is demonstrated on one side of the central limb of the intussusceptum. C, central limb of the intussusceptum; M, mesentery [From del Pozo (1999)]

Fig. 1.49a,b. Intussusception on longitudinal US scans. Variable appearance of intussusception on longitudinal US scans depending on which side of the central limb of the intussusceptum the mesentery is imaged. It may be depicted at one side (pseudo-kidney) or at both sides (sandwich). 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 shows the pseudokidney sign. The mesentery is demonstrated on one side of the central limb of the intussusceptum. C, central limb of the intussusceptum; M, mesentery [From del Pozo (1999)]

Mesenteric Lymph Nodes Intussusception
Fig. 1.50. Intussusception with lymph nodes (variant of the mesenteric crescent). Axial image at the base of the intussusception. The crescent-in-doughnut contains round mes-enteric lymph nodes (L). C, the entering limb of the intussusceptum [From del Pozo (1999)]

better detection and characterization of lead points than a contrast enema study (Miller et al. 1995; Navarro and Daneman 2004b). Transient small-bowel intussusceptions that may reduce spontaneously are not infrequently identified on US or on CT studies (Navarro and Daneman 2004a; Strouse et al. 2003).

Barium enema examination has been the standard of reference for the diagnosis of intussusception for many years. 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. 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. 1.53).

Fig. 1.51a,b. Intussusception with trapped peritoneal fluid. a Schematic representation of an intussusception with the presence of fluid. Sagittal and axial images were obtained at different levels. Fluid collects between the serosal layers of both limbs of the intussusceptum; the returning limb is everted and compromised. The mesentery acts as a wedge which makes the exit of fluid into the peritoneum difficult. Dilatation at the apex of the intussusceptum, probably secondary to ischemia and to the increase in trapped fluid, occurs mainly at the antimesenteric border. This fact results in the asymmetric disposition of the area of fluid, which explains the appearance on axial US images. 1, crescent-in-doughnut sign with additional anechoic crescent; 2, everted intussusceptum filled with peritoneal fluid; A, intususcipiens; B, returning limb of the intussusceptum; C, entering limb of the intussusceptum; M, mesentery. The black areas represent fluid in the intussusception. b US scan of an intussusception with trapped peritoneal fluid. Axial US scan shows the double crescent-in-doughnut sign (arrows). There is the crescent-in-doughnut sign with an additional echo-free crescent that represents the trapped fluid (F). M, mesentery [From del Pozo (1996b)]

Fig. 1.51a,b. Intussusception with trapped peritoneal fluid. a Schematic representation of an intussusception with the presence of fluid. Sagittal and axial images were obtained at different levels. Fluid collects between the serosal layers of both limbs of the intussusceptum; the returning limb is everted and compromised. The mesentery acts as a wedge which makes the exit of fluid into the peritoneum difficult. Dilatation at the apex of the intussusceptum, probably secondary to ischemia and to the increase in trapped fluid, occurs mainly at the antimesenteric border. This fact results in the asymmetric disposition of the area of fluid, which explains the appearance on axial US images. 1, crescent-in-doughnut sign with additional anechoic crescent; 2, everted intussusceptum filled with peritoneal fluid; A, intususcipiens; B, returning limb of the intussusceptum; C, entering limb of the intussusceptum; M, mesentery. The black areas represent fluid in the intussusception. b US scan of an intussusception with trapped peritoneal fluid. Axial US scan shows the double crescent-in-doughnut sign (arrows). There is the crescent-in-doughnut sign with an additional echo-free crescent that represents the trapped fluid (F). M, mesentery [From del Pozo (1996b)]

Fig. 1.52. Intussusception. Duplex Doppler sonography. Color Doppler indicates wall vascularity. High resistive index is observed in the vessels within the intussusception. This intussusception could be reduced

Fig. 1.52. Intussusception. Duplex Doppler sonography. Color Doppler indicates wall vascularity. High resistive index is observed in the vessels within the intussusception. This intussusception could be reduced

Fig. 1.53a-c. Barium enema. 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 intussus-cipiens and the intussusceptum. c Image from a barium enema study performed after complete reduction of the intussusception shows barium flowing freely into the ileum [From del Pozo (1999)]

Fig. 1.53a-c. Barium enema. 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 intussus-cipiens and the intussusceptum. c Image from a barium enema study performed after complete reduction of the intussusception shows barium flowing freely into the ileum [From del Pozo (1999)]

1.2.1.2 Treatment

Although there are reports of spontaneous reduction of intussusception (Swischuck et al. 1994; Navarro and Daneman 2004a), chronic and recurrent intussusceptions, and rare cases of spontaneous sloughing of the gangrenous intussusceptum through the rectum (Ravitch 1986), 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%).

Enema reduction is the standard non-operative method of treatment of intussusception. This may be guided with fluoroscopy when a barium, water-soluble, or air enema is used. US guidance is used when therapy is performed with a saline, water, or air enema. There is continuing discussion without vast agreement about which type of enema is the best for the reduction of intussusception. The few randomized studies that have been performed did not show statistically significant differences in reduction and perforation rates between air and liquid enemas (Meyer et al. 1993). The goal of any type of enema therapy is to reduce the intussusception by exerting pressure on the apex of the intus-susceptum to push it from the pathologic position back to the original position. The reduction and perforation rates for a specific type of enema therapy are directly proportional to the pressure applied. Ravitch (1986) found that the intracolonic pressure achieved by placing the barium enema bag 3.5 ft (105 cm) above the table did not reduce any intussus ception 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 (Shiels et al. 1993). 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 (Kuta and Benator 1990). This theoretical pressure is reached 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, the use of a rectal tube of large caliber may be more effective in increasing the actual intracolonic pressure than use of an increased column height (Schmitz-Rode et al. 1991). According to some experimental studies, the likelihood of perforation is smaller with the use of liquid compared to air enemas (Zambuto et al. 1995). There is no agreement on the number and duration of reduction attempts, the efficacy of pre-medication or sedation, the use of rectal tubes with inflatable retention balloons, or the use of transabdominal manipulation (Meyer 1992; Katz and Kolm 1992). This lack of agreement reflects the fact that no large studies have demonstrated a definite improvement in the reduction rate with any of these factors. According to the classic "rule of threes" the barium bag is suspended 3 ft above the examination table and three attempts over a maximum of 3 min are performed for reduction. 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 (Gonzalez-Spinola et al. 1999). Use of US guidance permits an even more liberal approach to enema therapy due to the lack of radiation exposure. Use of sedation had been thought to improve the reduction rate. However, sedation prevents the patient from performing the Valsalva maneuver during straining. This maneuver improves the effectiveness of enema therapy and protects against perforation, particularly during air enema therapy (Bramson et al. 1997). In theory, use of a rectal tube with a retention balloon creates a closed system that transmits the effective pressure of the enema material (liquid or air) without a loss of pressure. Use of such a rectal tube could increase the speed and effectiveness of enema therapy. However, this closed system could block the spontaneous expulsion of liquid or air when the pressure suddenly increases (Rohrschneider and Troger 1995).

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