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Signs in Imaging |
1 From the Department of Radiology, Medical College of Virginia of Virginia Commonwealth University, Main Hospital 3rd Fl, 401 N 12th St, Richmond, VA 23298-0615. Received March 13, 1998; revision requested April 24; revision received June 4; accepted June 24. Address reprint requests to the author.
Index terms: Gastrointestinal tract, diseases, 74.73, 75.73 • Gastrointestinal tract, US, 70.12981, 70.12983 • Intussusception, 74.73, 75.73
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The edematous intussusceptum is hypoechoic at US. The mesentery contains fat, vessels, and lymph nodes that may be scanned by using US. The fat is hyperechoic, and the lymph nodes and blood vessels are hypoechoic (1). These components of the intussusception cause its characteristic US findings, including the pseudokidney sign. In the sagittal scanning plane, the hypoechoic periphery is created by the edematous intussusceptum; the hyperechoic center is created by the mesentery. In the transverse scanning plane, the intussusception may have the appearance of a hypoechoic doughnut near the apex of the intussusceptum where the bulk of the appearance is created by the edematous bowel of the intussusceptum without contribution from the mesentery (1,8). At the more proximal portion of the intussusception, the hyperechoic mesentery is included with the intussusceptum, along with hypoechoic lymph nodes and blood vessels. This complex, together with the hypoechoic, edematous intussusceptum, creates the crescent-in-doughnut sign (1).
Although the US pseudokidney and doughnut signs of intussusception are highly sensitive and specific, they are not pathognomonic. Other causes of bowel wall edema, such as necrotizing enterocolitis, midgut volvulus, and sigmoid volvulus, may have similar US findings (8). False-positive findings, including feces in the colon, perforated Meckel diverticulum with malrotation and Ladd bands, psoas muscle, and hematoma, have been reported (5). The finding on transverse US scans of a hyperechoic crescent caused by mesenteric fat, together with hypoechoic foci caused by lymph nodes or blood vessels, is very characteristic of intussusception and may help to eliminate false-positive cases (1,9). A very thin (<6-mm) hypoechoic rim may help to distinguish hyperechoic feces from intussusception (5).
Color Doppler US may have a role in estimating the reducibility of an intussusception and in predicting bowel ischemia. When visualized, color signal may be uniformly distributed throughout the hyperechoic central and hypoechoic peripheral portions of the intussusceptum (10). Color signal within the intussusceptum appears to be a very good predictor of reducibility. Likewise, lack of color signal suggests that surgical intervention is likely to be needed. An intussusceptum without color signal may have associated necrosis, but this is not always true.
In four series totaling 225 intussusceptions, color Doppler US demonstrated blood flow in 204 (91%) of the 225 intussusceptions. Surgical intervention was required for 22 (11%) of the 204 intussusceptions with demonstrable blood flow versus for 17 (81%) of the 21 intussusceptions without demonstrable blood flow. Eight (47%) of these 17 cases without blood flow were found to involve necrotic bowel (6,7,10,11).
Intussusception is a common abdominal emergency in early childhood. Idiopathic intussusception occurs in two to four babies per 1,000 live births and is often associated with viral or other gastrointestinal conditions that cause enlargement of intestinal intramural lymphoid tissue. Seventy-five percent of intussusceptions occur in patients younger than 2 years, and boys are affected twice as often as girls. Up to 90% of cases are idiopathic, without a pathologic lead point (12). Pathologic lead points occur most frequently in infants younger than 3 months and in children older than 3 years (3). A variety of lead points have been reported, including Meckel diverticulum, duplication cyst, polyps, periappendicitis, polypoid hemangioma, Burkitt lymphoma, and ectopic pancreas (12,13). Coagulopathies and Henoch-Schönlein purpura also may have a role in intussusception (12).
Intussusception is much less common in adults, who represent 5% of all patients with this condition. In a series of 58 intussusceptions in adults, 27 (47%) were caused by malignancies. Therefore, surgical resection is the primary management for intussusception in adults (14).
Ileocolic is the most common form of intussusception (75%–95%) (2). Ileoileocolic intussusceptions are the second most common, followed by ileoileal and colocolic intussusceptions (2,4). In two series totaling 96 intussusceptions, 87 (91%) were ileocolic, and the other nine (9%) were ileoileocolic (15,16). About 90% of intussusceptions are found in the transverse hepatic flexure and ascending portions of the colon; the majority are found in the transverse colon (15).
The signs and symptoms of intussusception include abdominal pain, bloody stool, emesis, a palpable abdominal mass, and diarrhea. The pain may be intermittent and cause the child to curl the knees into the abdomen. Sometimes, a depression in the right lower region of the abdomen may be palpable when the cecum is drawn into the upper part of the abdomen secondary to the intussusception (12). Less than 50% of patients exhibit the classic clinical triad of abdominal pain, red currant jelly stool, and a palpable abdominal mass (9). Other signs and symptoms may include restlessness, pallor, and fever (15,16).
The radiographic diagnosis of intussusception is generally made by using conventional radiography, contrast or air enema examination, and US. Several publications (2,3,9,13,15–17) have addressed the former two diagnostic methods. US with recognition of the pseudokidney sign may be up to 100% sensitive and specific for the diagnosis of intussusception (10). Therefore, the pseudokidney sign and its correlate signs may be very helpful in the successful diagnosis of this common pediatric abdominal emergency.
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This article has been cited by other articles:
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  N. Mumoli, G. Niccoli, M. Cei, and C. Bartolomei The Pseudokidney Sign Journal of Diagnostic Medical Sonography, July 1, 2008; 24(4): 257 - 259. [PDF]
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