Background
Congenital small bowel atresia (SBA), including duodenal, jejunal, and ileal atresia, is a common cause of neonatal intestinal obstruction, with an incidence ranging from 1.3 to 2.8 of 10,000 live births [
1]. Prenatal ultrasound can be used to diagnose intestinal obstruction, but it can only play a role of preliminary screening for SBA, as dilated bowel loops and polyhydramnios provide a low overall detection rate [
2,
3]. Neonates with SBA need further examination for diagnosis after birth. Diagnosing neonatal SBA primarily depends on clinical manifestations and imageological examination. Plain abdominal radiographs can be used to investigate intestinal obstruction. Upper gastrointestinal contrast studies can identify obstruction levels and rule out volvulus and malrotation diseases [
4]. A contrast enema helps investigate suspected Hirschsprung disease [
5]. Although barium and water-soluble enema can detect microcolon and facilitate SBA diagnosis, the radiation and risk of intestinal perforation have led many scholars to recommend minimising their use [
6‐
9]. Ultrasonography (US), a safe, convenient and inexpensive imaging method, is suitable for neonates because of their thin abdominal wall. The microcolon without gas, significantly smaller than a normal colon, can be used to diagnose SBA by US [
10]. However, no standard colonic measurement is available for new-borns because of the lack of consistency in US scans. Moreover, there is no standard diametric value for diagnosing SBA, which limits the diagnostic ability of clinical sonographers. A better US method for differentiating patients with SBA from those without SBA could reduce the need for contrast enema and upper gastrointestinal contrast. Therefore, this study aimed to evaluate colon accuracy and other characteristics for diagnosing SBA by US, using surgical or clinical information as the reference standard.
Discussion
Only a few ultrasound studies have focused on the neonatal intestine, possibly because it can be interfered by intestinal gas and stool mass. However, many intestinal diseases can be diagnosed by US even with interference [
11‐
14]. US has become an important diagnostic method in many children’s diseases, including intussusception [
15], intestinal malrotation [
16,
17], and intestinal polyp [
18]. US is important to neonates in diagnosing necrotising enterocolitis [
19]. The proximal intestine is often dilated for neonates with SBA, filling with amniotic fluid or milk. In contrast, to avoid aspiration and relieve pain, clinicians usually carry out gastrointestinal decompression for neonates when an intestinal obstruction is suspected, which leads to the production of more intestinal gas, relieves the dilation state, and disturbs doctors from finding the dilated bowel. The distal SBA intestine was not affected by swallowing and gastrointestinal decompression. Since no amniotic fluid and milk were passed, the distal intestine (including the colon and a part of the small bowel) remained in a state of reduction for a long time. It only has a little meconium content and is without any gas. These characteristics are easily detected on ultrasound and can be used to distinguish other types of intestinal obstruction. Briefly, the present study examined the distal small bowel and colon characteristics to determine the accuracy of the SBA diagnosis.
The microcolon has been recognised and proposed by surgeons for nearly 100 years [
20]. It has now become an important basis for contrast enema in diagnosing SBA; however, it was barely mentioned on the US. Although Hao [
10] reviewed the ultrasonographic findings of 19 neonates with SBA and confirmed that US could detect microcolon without gas, the study did not provide the criteria of microcolon and the data on false-negative and -positive rates. To ensure consistency, we selected a transverse view of the left kidney showing the short colonic axis for measurement. This area was chosen because the anatomic locations of the descending colon are more constant and hardly disturbed by intestinal gas at the specified section. Finding a colon requires some experience and patience. Gentle pressure is applied, if necessary, to avoid the influence of crying. Furthermore, there is a need to avoid treating dilated small bowel as colon. In this study, five neonates had an unclear or unexplored colon. In addition to the high display rate (93.0%, 67/71), the colonic diameter of the study group was significantly smaller than that of the other two groups, indicating that the colonic diameter has a more intuitive value in SBA diagnosis. Combined with the cut-off value of the ROC curve, we believe that the ultrasonic colon with a diameter of < 0.65 cm has the maximum predictive value for SBA, called ultrasonic microcolon. On ultrasound, SBA can be ruled out when the colon diameter is > 0.85 cm.
We postulated that distal micro small bowel might be a secondary change of the SBA due to prolonged complete obstruction. But it is difficult to assess and make repeatable measurements. Because these distal micro small bowel perform small, peristalsis slower, have no fixed location, and are often obscured by dilated intestines. For atresia of or near the ileocecal junction, the micro small bowel may be absent or difficult to find [
7]. We performed a periumbilical scan to find the section with the smallest intestine and the least intestinal gas for analysis. The diameter was < 0.6 cm and without wriggle, defined as the micro small bowel. Moreover, all neonates with SBA not only had micro small bowel but were also gas-negative. However, the micro small bowel was also present in the study group without SBA and the control group. It may be because the neonates have not accumulated food in the intestinal tract soon after birth. In particular, some neonates with heavy intestinal stenosis in the study group without SBA have a high proportion of micro small bowel.
Gas-negativity in the distal intestine is an essential diagnostic basis for SBA. Excluding few individuals has a biliary fistula [
21]. In the study group without SBA, neonates without colonic gas were mostly patients with severe intestinal obstruction. In the control group, there was only one case of a 4-hour-old new-born, the youngest neonate, with a gas-negative colon. The gas in the intestinal lumen had not moved to the colon because the neonate did not eat much after birth. This shows that the absence of gas in the colon could be physiological during the first 4 h of their life. Since the amount of gas can be changed over time, finding a micro-small bowel without gas requires more experience, it cannot be an independent SBA diagnosis. Similarly, we did not find a time point for detecting false-positive gas negativities in the small bowel.
The current findings do not justify using colonic ultrasound as a substitute for contrast enema in diagnosing SBA; however, our study provides clinicians and neonates with more options. For neonates with suspected SBA, US can be done first; if SBA can be diagnosed, contrast enema administration may be cancelled. The difference in diagnostic accuracy between US and contrast enema requires further clarification.
Our study had some limitations. Firstly, although our study spanned 2 years, we did not have enough cases, including the control group of normal new-borns, because they rarely received routine abdominal ultrasounds. More clinical data need to be accumulated for comparison in differentiating colonic diameter between SBA and other diseases, including meconium ileus, even if no case was gathered in this study. Secondly, it is challenging to determine accurately the amount of micro small bowels, and the amount of gas in it can change over time. The results may vary depending on the doctor’s experience. Thirdly, considering the benefits of timely gastrointestinal decompression, we could not require eliminating gastrointestinal decompression in suspicious SBA neonates before US. Therefore, proximal bowel dilation was not analysed in this study. However, contrast enema or upper gastrointestinal contrast cannot be performed before an ultrasound examination is still required.
Publisher’s Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.