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1 Department of Diagnostic Radiology, Myongji Hospital, Kwandong University, College of Medicine, 697-24 Hwajung-dong, Dukyang-ku, Koyang, Kyunggi 412-270, 2 Department of Preventive Medicine, Cheju National University, College of Medicine, 154 3-do-2-dong, Jeju City, Republic of Korea
Correspondence: Dr Noh Hyuck Park, Diagnostic Radiology, Myongji Hosp, Kwandong University, College of Medicine, 697-24 Hwajung-dong Dukyang-ku, Koyang, Kyunggi 412-270, Republic of Korea. E-mail: nhpark904{at}kwandong.ac.kr
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Abstract |
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Introduction |
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In the recent literature [3–5], careful ultrasonographic examination and/or interpretation of CT scans have disclosed many SBIs that were reduced spontaneously without any intervention. Conservative observation was warranted in these patients and Doi et al [5] have suggested the term benign SBI for idiopathic transient SBI.
Transient SBI, which does not require immediate treatment, should be distinguished from ICI, which does require urgent non-surgical or surgical reduction. The purpose of this article is to evaluate the typical ultrasonographic findings of transient SBI and to differentiate it from ICI in paediatric patients.
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Methods and materials |
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The ultrasonographic examination was performed by a paediatric radiologist using the HDI 5000 (Advanced Technology Laboratories, Bothell, WA). After scanning the solid abdominal organs using a convex transducer, a 5–12 MHz linear transducer was then used for the detailed evaluation of the bowel and mesentery. Ultrasonographic criteria for the diagnosis of intussusception consisted of the presence of one or more characteristic sonographic signs: a doughnut sign (an even thickened hypoechoic outer and a central hyperechoic core), a crescent-in-doughnut sign (an even outer hypoechoic rim with a central hyperechoic crescent) or a multiple concentric rings sign (a mass with multiple alternating hypoechoic and hyperechoic concentric rings).
The location of the intussusception was documented according to the site of its head: the right upper, right lower, left upper, left lower, periumbilical or epigastric region. The diameter and the thickness of the outer sonolucent rim (outer wall to the luminal surface) of the intussusception were measured on transverse scan by using the electronic callipers of the ultrasonography equipment or the picture archiving and communication system. The presence or absence of mesenteric lymph nodes in the intussuscipiens was evaluated.
Pneumoreduction was attempted in all patients with suspected ICI, whereas patients with suspected transient SBI were managed conservatively. In the suspected transient SBI patients, follow-up ultrasonography was performed 1–2 days after the initial examination to check for the persistence or disappearance of the transient SBI. All images were reviewed by an experienced paediatric radiologist with more than 5 years' experience.
For comparison of the anteroposterior diameter and thickness of the outer rim of the SBIs and ICIs, the Wilcoxon rank sum test was applied. p values less than 0.001 were considered to indicate statistically significant differences.
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Results |
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On ultrasonography, transient SBI appeared as a crescent-in-doughnut (Figure 1a
) or multilayered round mass on a transverse scan, and the short segmental sandwich sign (Figure 1b) was seen on a longitudinal scan. In the SBIs, the head of the intussusception was located in the right lower quadrant in 11 cases (50%), the right upper quadrant in 2 cases (9.1%) and the periumbilical area in 4 cases (40.9%). In the ICIs, the head was located in the right upper quadrant in 17 cases (63%), the epigastric area in 7 cases (25.9%) and the left upper quadrant in 3 cases (11.1%) cases.
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) whereas 26 of the ICI cases (96.3%) contained mesenteric lymph nodes (Figure 2). Table 1 summarizes the difference between transient SBI and ICI in this study.
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In three patients the SBI was reduced before completion of the initial ultrasonographic examination. In the remaining 19 patients with SBI, repeated ultrasonography was performed within 2 days of the initial examination and none exhibited persistent SBI. One patient underwent CT scan for evaluation of bowel ischaemia or perforation, but this was negative and the patient was finally diagnosed with acute gastroenteritis. The final clinical and ultrasonographic diagnoses of transient SBI were acute gastroenteritis with secondary mesenteric lymphadenopathy (12 cases), urinary tract infection (1 case), terminal ileitis with mesenteric lymphadenopathy (2 cases), ileocolic intussusception (1 case), primary mesenteric lymphadenitis (3 cases) and non-specific abdominal pain (3 cases).
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Discussion |
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A high percentage of cases of transient SBI was observed in a recent ultrasonographic study in children [13]. This may be related to the increased use of abdominal ultrasound in children presenting with abdominal pain and secondary to the improvement in resolution and quality of the images.
In general, transient SBI occurred in older children (mean age 4 years) compared with large bowel intussusception (less than 2 years). Transient SBI patients commonly presented with non-specific symptoms, such as vomiting, irritability with crying, fever and/or abdominal pain, or with symptoms characteristic of intussusception, such as cyclic abdominal pain, a palpable mass and red currant jelly stool, which occurred in approximately one-fifth of patients. Therefore, diagnosis based on clinical examination can be problematic unless imaging studies are performed [2]. In many instances, the causal relationship between the symptoms and SBI is uncertain. Many of the patients have additional problems, such as acute viral gastroenteritis, mesenteric lymphadenopathy, large bowel intussusception, HSP (Henoch–Schönlein purpura) and the post-laparotomy state, all of which may be the causal factor of the abdominal symptoms. SBI may also occur incidentally in asymptomatic patients. The following factors are thought to predispose children to develop SBI: (a) swelling of the bowel wall; (b) abnormal gastrointestinal motility; and (c) scar or adhesion of the bowel from previous insult [3].
Sonography has been reported to be highly sensitive (98–100%) for the diagnosis of intussusception [9, 10, 14]. Tiao et al [15] also reported that the sensitivity of sonography for detecting SBI among paediatric patients was 84% (11 positive findings from 13 initial sonograms), although a detailed sonographic evaluation of the abdomen may occasionally be limited by excessive bowel gas in the dilated bowel loops and the irritability of the patients.
The sonographic appearance of ICI is variable and depends on the extent of enclosed mesentery and the segment between the apex and basal part of the lengthy intussusceptum that is being scanned [14]. The presence of trapped peritoneal fluid within an intussusception is found in about 14% of cases of ICI [16], which correlates significantly with ischaemia and irreducibility. On axial US scans, this complication appears as the double-crescent-in-doughnut sign. This finding was not seen in any of our transient SBI patients.
Transient SBI in paediatric patients is more difficult to detect because the lesions are usually smaller and atypically located and, thus, more experience is necessary.
The most outstanding difference between SBI and ICI is the size of the intussusception. The transient SBI tends to have a smaller diameter and a thinner outer rim than the ICI. The transient SBI contains less mesenteric fat and no lymph nodes compared with the ICI, and this is probably due to a short segmental invagination.
In one report, real-time evaluation on the video records showed peristalsis of the invaginated bowel wall in all of the 14 transient SBI patients that were recorded [2]. Visible wall motion on real-time ultrasound observation may also suggest an early reduction. This finding can also differentiate SBI from ICI [2].
Despite the sonographic identification of various lead points, such as enterogenous cyst, lipoma, lymphangioma, Meckel's diverticulum and Peutz–Jeghers syndrome, in cases of SBI [17–20], it was very difficult to find the underlying lesions preoperatively on ultrasonogram [15]. CT has been reported to be a sensitive examination for the diagnosis of intussusception and the demonstration of the presence of associated lead points. In addition, it provided an excellent preoperative evaluation of the possible extension and/or dissemination of a malignant tumour, if present, and was also helpful in excluding other abdominal conditions [11, 12]. Nevertheless, the routine application of CT for all paediatric patients with non-specific abdominal symptoms and signs is of doubtful use. If the ultrasonographic finding is typical of transient SBI, the patient may be managed conservatively and ultrasonographic follow up seems to be sufficient for subsequent monitoring to confirm a spontaneous reduction as long as it is performed by an experienced radiologist [2]. Therefore, CT should not be required, avoiding unnecessary radiation exposure to the patient. Because most cases of transient SBI resolve quickly, we suggest that the timing of follow up should be 1 h or at least within 1 day from the initial examination.
Although SBI that needed surgical intervention were not included in our study, transient SBI should be differentiated from these cases. Transient SBI tends to have a smaller diameter (mean 1.38 cm in our study) than surgically managed SBI [21], which in this study had a mean outer diameter of 2.9 cm (range 2–4.3 cm), overlapping with the size range of ICI in our study (1.89–3.32 cm with a mean diameter of 2.53 cm). The lesion generally gets larger as swelling of the bowel wall progresses, as was demonstrated by the different outer rim thicknesses in the two groups (mean 0.26 cm vs 0.72 cm for the transient and surgically managed SBIs, respectively). The lead point contained within the intussusception may also increase the size, which occurred in 46% of the surgically managed SBI cases [21], Other ultrasonographic findings known to be associated with difficult reduction of the intussusception include the presence of bowel obstruction, free fluid and fluid trapped between the intussuscepted bowel walls [22], all of these which were more frequent in the patients with surgically managed SBI.
The reported rates of post-operative SBI in children have ranged from 4% to 16%. The reported incidence is even higher in patients with neuroblastoma and in trauma patients after laparotomy. The diagnosis of post-operative SBI remains challenging because its clinical presentations mimic the common post-operative complaints of abdominal pain, vomiting and ileus, and radiographic imaging studies are usually inconclusive. Therefore, close ultrasonographic follow up for patients after surgery should be carried out for possible SBI [21].
This study was limited by the lack of pathological correlation in small bowel intussusceptions because of their spontaneously resolving nature, which made surgery unnecessary.
In conclusion, when compared with ICI, the transient SBI is seen predominantly in the right lower quadrant and periumbilical region and has a smaller diameter and a thinner outer rim. It does not contain mesenteric lymph nodes within the intussuscipiens.
Knowledge of these ultrasonographic findings of transient SBI will be helpful in differentiating this condition from ICI, which requires urgent reduction.
Received for publication August 7, 2006. Revision received December 13, 2006. Accepted for publication January 2, 2007.
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