| BackgroundNecrotizing enterocolitis(NEC)is a kind of intestinal mucosal damage caused by premature birth,infection,ischemia,hypoxia and other reasons.It is a serious life-threatening disease in the neonatal period.The definition of NEC was first proposed by Schmid in 1953,but so far,its etiology and pathogenesis have not been fully understood.It is generally considered to be caused by a combination of multiple factors,including multiple "I"s,such as immaturity,infection,ingestion,ischemia,insufficient,injury,and immunological factor.These factors all affect the blood supply of the intestinal mucosa,mucosal ischemia,and weaken intestinal peristalsis.Bacteria multiply in the intestinal lumen and intestinal wall,producing a large number of inflammatory mediators,causing diffuse or spotted intestinal necrosis or gas accumulation in the intestinal wall.The scope of the disease varies,and it can involve single or multiple intestinal tracts.The clinical manifestations of NEC vary greatly.It can be manifested as typical gastrointestinal symptoms,such as abdominal distension,vomiting,diarrhea,hematochezia or systemic non-specific sepsis symptoms,even worse,shock or even multiple ogran failure.At present,the revised Bell-NEC staging standard is often used to evaluate the severity of NEC.Stage I is suspected of NEC,manifested as gastric retention,mild abdominal distension,and positive stool occult blood;stage Ⅱand stage Ⅲ are confirmed cases of NEC.Stage Ⅱ cases manifested as hematochezia,disappearance of bowel sounds,abdominal tenderness,abdominal wall cellulitis,accompanied by systemic symptoms such as mild acidosis and mild thrombocytopenia.Stage Ⅲ progresses to diffuse peritonitis and abdominal distension on the basis of stege Ⅱ Exacerbation,accompanied by obvious tenderness and swelling of the abdominal wall,intestinal perforation in severe cases,and systemic symptoms such as hypotension,bradycardia,severe apnea,mixed acidosis,DIC,neutropenia,and anuria.The treatment plan of NEC varies greatly depending on the severity of the disease.According to the revised Bell-NEC staging standard,children with stage Ⅰcan be improved or cured by fasting,gastrointestinal decompression and 3 days of antibiotic treatment;children with stage Ⅱ requires absolute fasting,blood volume supplementation,correction of acidosis,and antibiotic application 7-14 days,patients with poor results of conservative medical treatment in internal medicine require surgery.Children with stage Ⅲ are in serious condition,surgical treatment is required after conservative treatment fails.The long-term prognosis of children with stage Ⅰand stage Ⅱ is good.The survival rate of patients cured by conservative medical treatment is 80%,and the survival rate of children undergoing surgical treatment is about 50%,among them 25%accompanied by long-term gastrointestinal sequelae.Intestinal stricture is one of the common complications after NEC.It is mainly manifested as repeated abdominal distension,vomiting,feeding intolerance,lack of specificity.It can cause growth retardation and even intestinal obstruction.The transition from medical treatment to surgery is a key decision point in the management of NEC,which has an important impact on the clinical outcome of NEC.Since the acute stage of NEC may rapidly develop into intestinal perforation,peritonitis,and shock,timely diagnosis and treatment are extremely important to improve the prognosis.In addition,surgery is the only effective method for the treatment of intestinal stricture post-necrotizing enterocolitis,but the early symptoms of intestinal stricture post-necrotizing enterocolitis is lack of specificity and are easy to be missed or misdiagnosed.Therefore,it is important to identify NEC signs that require surgery as soon as possible.The traditional view is that abdominal X-ray is the preferred imaging for evaluating the condition of NEC.However,X-ray manifestations are generally later than clinical and are not sensitive to minimal changes.The X-ray features of NEC have great variability,overlap with other intestinal lesions,and are limited in reflecting disease progression.Repeated bedside X-ray examinations in short term have potential radiation hazards to children and medical staff.CT can clearly show the pathological changes,but most severely ill children cannot carry an assistive breathing device for examination.Gastrointestinal angiography can help determine the location of intestinal obstruction,but it is not suitable for children with potential perforation risk.In recent years,the application of ultrasound in the field of intensive care has developed rapidly.The neonatal abdominal wall is thin,which is conducive to the penetration of ultrasonic wave and the image is clear,which can provide more clinical information.The 2016 "Experts Consensus on Necrotizing Enterocolitis" clearly pointed out that bedside ultrasound can sensitively detect signs of bowel necrosis such as disappearance of peristalsis,thickening of the bowel wall,and gas accumulation in the bowel wall,which helps clinicians to diagnose early and accurately grasp the timing of NEC surgery.Studies have shown that intestinal ultrasound can provide more information for judging the condition of high-risk children,so that more aggressive treatment can be adopted.Bedside ultrasound is especially suitable for premature infants who are critically ill and require ventilator support.However,it is not clear which image features of intestinal ultrasound can provide the most useful reference information for surgery.Superbmicrovascular imaging(SMI)is a new Doppler ultrasound imaging technology.It used advanced clutter suppression technology to extract the flow signal of tiny blood vessels without using contrast medium.Small blood vessels and low-velocity blood flow signals were displayed at a high frame rate.It provided two modes:color SMI(cSMI)and monochrome SMI(mSMI).The former is a color blood flow imaging mode,and the latter is a monochrome mode,improving sensitivity by filtering out background information.During the ultrasound examination in young children,especially newborns,it is often difficult to hold their breath.The resulting motion artifacts often result in insufficient image clarity,and SMI can reduce the motion artifacts caused by breathing.In recent years,SMI has been frequently reported in pediatric ultrasound examinations.There has been researches about SMI diagnosis of thyroid,parotid gland,testis disease and bladder wall blood perfusion.By using mSMI,Yasuharu found a hypertrophic mucosal layer associated with hypervascular changes was clearly seen.Yumin Wang found the blood classification of SMI was positively correlated with enema reset rate.These studies provide important reference value for the application of SMI in intestinal diseases.NEC is a common disease in neonatal period.In the past years,color doppler flow imaging(CDFI)was used to observe ischemia and necrosis in the intestinal wall.Howerer,CDFI is not sensitive enough to low-velocity blood flow.When surgery was performed on some children whose intestinal wall does not show blood flow signal by CDFI,it often been found that the intestinal wall was not completely necrotic.SMI can display low-velocity blood flow signals more clearly,and reduce motion artifacts caused by breathing.It can reflect the blood supply of intestinal wall more accurately.As a non-invasive examination,SMI can show the vascular structure of the lesion in detail without the use of contrast agents and other invasive procedures.The intestinal wall of neonates is relatively small,so we chose cSMI to evaluate the blood supply of the NEC neonates.In summary,this study is divided into three parts.In the first part,high-frequency ultrasonography and color Superb microvascular imaging was used to clearly diagnose NEC by observing intestinal peristalsis,intestinal morphology,intestinal wall echo,thickness,intestinal wall gas,portal vein gas,and blood perfusion.According to the situation,the differences in ultrasound image characteristics between children with confirmed NEC and children with suspected NEC and the differences in hemodynamic parameters of superior mesenteric artery(SMA)were compared,and the ultrasound image characteristics that could diagnose NEC were screened out.The second part aims to explore the predictive value of commonly used ultrasound image features for acute NEC surgery.By retrospectively analyzing the color Doppler ultrasound image features of children with NEC,compare the differences in ultrasound image features between the surgical group and the non-surgical group.Logistic regression analysis was performed according to the results of single factor analysis,and the joint predictor was calculated.ROC curve analysis was performed on the combined predictor and single factor,and the sensitivity and specificity of the combined predictor and single factor were calculated to predict the acute phase of NEC surgery.The advantages and disadvantages of ultrasound and X-ray images of newborns undergoing acute NEC surgery were compared.In the third part,the value of intestinal ultrasound in the diagnosis of intestinal stenosis post-NEC was discussesed by summarizing the performance of intestinal ultrasound in children with NEC posterior intestinal stenosis.Objective1.Neonatal intestinal peristalsis,intestinal morphology,intestinal wall echo and thickness,intestinal wall gas,portal vein gas and blood perfusion were observed to compare the ultrasound findings of newborns with confirmed NEC and newborns with suspected NEC by high-frequency ultrasonography and color Superb microvascular imaging.2.To compare the differences in hemodynamic parameters of SMA between the groups with confirmed NEC and suspected NEC.The hemodynamic parameters of SMA in the two groups were measured.3.To explore the predictive value of ultrasound image features for acute NEC surgery by analyzing the color doppler ultrasound image characteristics of NEC in the surgical group and the non-surgical group,and comparing the differences in the ultrasound image characteristics between the two groups.Logistic regression analysis was performed based on the results of the univariate analysis to screen indicators that can predict surgery.4.To screen out the examination methods or image features that are valuable for predicting NEC acute surgery by comparing the advantages and disadvantages of ultrasound and X-ray images of children undergoing acute NEC surgery.5.To evaluate the diagnostic value of bowel ultrasound for intestinal stricture post-necrotizing enterocolitis by observing the intestinal morphology,peristalsis,and echo of the intestinal wall in newborns with NEC posterior intestinal stenosis.Part Ⅰ The value of high-frequency ultrasonography and color Superb microvascular imaging in diagnosing necrotizing enterocolitis.Materials and MethodsHigh-frequency ultrasonography and color Superb microvascular imaging were performed in 70 newborns with confirmed NEC and 58 newborns with suspected NEC from January 2017 to March 2021.The image characteristics were retrospectively analyzed,including bowel movement,bowel wall thickness and bowel wall gas,portal gas,blood perfusion,and abdominal effusion.The differences in the hemodynamic parameters of superior mesenteric artery(SMA)including peak systolic velocity(PSV),end diastolic velocity(EDV),resistance index(RI)between the two groups were compared.The measurement data were compared by t-test,and the count data was compared by chi-square test to screen out positive indicators that are valuable for the diagnosis of NEC.ResultsThere was significant difference between CDFI and cSMI in the display of intestinal wall blood perfusion.For the same group of neonates,cSMI could raise the CDFI blood flow classification level.There was significant difference between the two groups in pneumatosis intestinalis,portal venous gas,weakened intestinal motility,thickened intestinal wall,rich blood flow,ascites depth,EDV of SMA and RI(P<0.05).There was no significant difference in PSV of SMA(P>0.05).Part Ⅱ High-frequency ultrasonography and color Superb microvascular imaging for predicting acute surgery of necrotizing enterocolitisMaterials and MethodsSeventy neonates with NEC were divided into operation group(22 cases)and no-operation group(48 cases).The ultrasound image characteristics were compared between the two groups.Logistic regression analysis was performed based on the results of single factor analysis.The combined predictor was calculated according to the results of Logistic regression analysis.ROC curve analysis was performed on the combined predictor and single factor.The X-ray image characteristics of the operation group including intestinal obstruction,intestinal dilatation,bowel wall gas,portal gas,abdominal effusion were observed in the operation group.The chi-square test was used to compare the character of X-ray and ultrasound in operation group,and the sensitive imaging signs of X-ray and ultrasound were screened out.ResultsThere was significant difference between the two groups in weaken peristalsis,pneumoperitoneum,ascites depth and ascites properties(P<0.05).According to the result of Logistic regression analysis,the weaken peristalsis,ascites depth combined with ascites properties were used to predict acute surgery of NEC,the area under the ROC curve was 0.951,the corresponding sensitivity and specificity were 95.5%and 85.4%.The area under the ROC curve was 0.894 according to the ascites depth,the corresponding sensitivity and specificity were 90.9%and 79.2%.The detection rate(50%)of free gas in the abdominal cavity of the operation group by abdominal X-ray was significantly higher than that of ultrasound(9%),while the detection rate of gas in the intestinal wall(36%)was lower than that of ultrasound(77%).Part Ⅲ The value of high-frequency ultrasonography in intestinal stricture post-necrotizing enterocolitisMaterials and MethodsThe ultrasound image characteristics of 28 infants with bowel stenosis post-necrotizing enterocolitis were retrospectively analyzed,including intestinal morphology,echo,blood perfusion,bowel wall thickness,adjacent bowel morphology,and surrounding mesentery.ResultsAmong them,there were 16 cases with single stenosis,12 cases with multiple stenosis.The main characteritics of intestinal stricture post-NEC were thicken of bowel wall,hypoechoic and rich blood flow signal in bottleneck.The intestinal lumen was obviously narrow,with stiff shape.The proximal intestine was dilated,and the multi-segmental stenosis manifest as a dumbbell.Conclusion1.It showed that weakened bowel motility,thickened intestinal wall,rich blood flow,gas in the intestinal wall,gas in the portal vein,and fluid in the ascites in innfants with confirmed NEC.The end diastolic velocity of SMA was lower and the resistance index was higher in group with confirmed NEC.2.Bowel ultrasound could effectively assess peristalsis,ascites depth and ascites properties,the combination of these indicators has high practical value for predicting acute surgery of NEC.3.X-ray was more sensitive to the recognition of free gas in the abdominal cavity than ultrasound.Free gas in the abdominal cavity and intestinal obstruction could be used as X-ray indicators to predict acute surgery in infants with NEC.4.The combined application of abdominal ultrasound and X-ray could improve the diagnostic efficiency of NEC intestinal perforation and intestinal necrosis.5.Intestinal ultrasound could clearly diagnose intestinal stenosis post-NEC,which was characterized by stiff intestinal morphology,small lumen,thickened intestinal wall,reduced echo,and abundant blood flow;proximal intestinal tract dilation,distal emptiness,and multiple stenosis manifestations Dumbbell shape. |
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