Research Of The Value Of Area Of Superior Mesenteric Artery-aorta In Diagnosis Of Superior Mesenteric Artery Syndrome

The research purpose and significance:Vascular compression of the duodenum causing obstruction and dilatation was first described by Rokitansky in 1861. Many names have been used to describe the condition, such as Wilkie’s syndrome, cast syndrome, and more recently, superior mesenteric artery syndrome (SMAS). SMAS is uncommon and characterized by postprandial epigastric pain, nausea, vomiting, and anorexia and weight loss. The syndromeis caused by compression of the third part of the duodenum in the angle between the aorta and the superior mesenteric artery. Females and young adults (18-35 years) are more likely to be affected by the condition, thought it can occur at any age. Standing or laying supine position after eating make the symptoms worse, prone position or knee-chest posture can relieve it. Currently on superior mesenteric artery syndrome treatment methods differ, most scholars think preferred conservative treatment methods, including postural therapy and fasting, gastrointestinal decompression, total parenteral nutrition, waiting for the relief of symptoms, weight gain can be a gradual transition to enteral nutrition and eventually return to normal diet and cure. Surgical treatment is the fundamental method for the treatment of the disease, the majority of patients with conservative treatment is invalid. But surgery may not be able to make all or cure, scholars have pointed out, when duodenal obstruction time more than two and a half years who, due to duodenal motility function has been changed, i.e., the inverse creep in clockwise peristalsis, pyloric canal opening, more frequent vomiting, especially has formed a "habitual" reverse peristalsis, even surgical relief of the obstruction, the strong antiperistaltic also cannot be eliminated, vomiting symptoms still can not be solved, so early diagnosis of the disease and treatment as soon as possible become particularly important.SMAS imaging methods include X-ray barium meal examination, CT examination, and ultrasonography and MRI examination. X-ray barium meal examination is still the primary examination for the diagnosis of SMAS, this method is simple and cheap, it also has advantage in terms of dynamic observation, but it can’t display anatomical relationship between SMA and AO or rule out other diseases. Ultrasonography is convenient, no radiation, but not intuitive, not sensitive in the expansion of the stomach and duodenum, and influenced by the operator subjective factors easily. CT can show the expansion of the stomach and duodenal intestine clearly. Using the technology of MPR in CT contrast enhanced imaging, can show the angle and the distance between SMA and AO, mesenteric fat, and SMA duodenal oppression clearly, while excluding other diseases. In recent years, multislice CT angiography combined with MPR and CTA becomes noninvasive and effective technique in diagnosis of SMAS. MR angiography (MRA) can show abdominal arteries intuitive, no radiation. Compared with CT, MRA image relative lack of spatial resolution, and vulnerable to a variety of factors interference, such as breathing exercises, pulsatility and bowel movements and other factors. Therefore, CT is better than MRI in the image displayed on the abdominal anatomy.The reason of the pars horizontalis duodeni compressed by SMA is usually considered to congenital anatomic factors and retroperitoneum of fat loss which caused by mechanical factors. In normal conditions, the fat of retroperitoneum and lymphoid tissue around the starting of SMA is very important to keep the angle and distance between SMA and AO. The fat of peritoneal reduction will reduce the angle and distance between SMA and AO. SMA origin of the lower and the Treitz ligament shortening are considered the main congenital anatomical factors. The two factors can lead to SMAS. Body mass index (BMI) are commonly used to measure the degree of body fat, it can evaluate underweight, overweight and abdominal fat content. Many scholars have carried on the research to the above factors, in which research is the most focusing on the angle and distance of the SMA-AO and theirs correlation with BMI. From the above, there are so many researches about the Angle and distance of SMA and AO, and their relationship with the BMI. They concluded the approximate result and reference range.In my opinion, measure the angle and distance of SMA-AO is not enough to evaluate the SMAS. We can’t ignore the factor that the distance of SMA starting to duodenal level. So, we should choose a more comprehensive and effective method. The area of the SMA-AO measured in the image of CT enhancement on sagittal MIP can take the two distances and angle into consideration. According to the human anatomy knowledge and geometry knowledge, it’s easy to draw the above three variables is positively correlated with the area, the reduction of any one factor can increase the risk of SMAS. So, using this area to assess SMAS is feasible. So far, there is no research about this area. Our research is about the measurement standards for the area and discussing this area can be used for the diagnosis of SMAS or not. At the same time, we will compare its value to the previous studies. The purpose of this study is mainly to investigate the area (angle and distance) of SMA-AO whether differences in the normal patients and patients with SMAS, find which the best indicator is, and Evaluate their correlation with BMI. At last, Analysis BMI can judge Screening of SMAS or not.Materials and methods:1. Materials and methods1.1 The object of study:Selection of 24 adult patients of SMAS who had undergone abdominal CT and X-ray barium meal examinations performed in our department over a 7-year period (2007-2014). The mean age of the SMAS patients was 36.2±11.6 years, range 19 to 59 years, and the BMI range from 16.4 to 21.1 kg/m2. All the SMAS patients had no abdominal operation history. All the SMAS patients have been carried out on digestive tract X-ray barium meal and CT scan of the upper abdomen enhanced scan, and the barium meal clearly show the duodenal stasis product change, enhanced CT examination have been excluded from the duodenum, superior mesenteric artery, abdominal active vein lesion and the surrounding exist in other pathological pressure change. On the other hand, we searched 209 adult non-SMAS patients who had undergone abdominal CT examinations performed in our department over a 10-month period (2013.7-2014.5). In order to reduce the influence of different size on the results, we select which the BMI range 16 to 20 kg/m2.There are 42 ones meet the requirement. None of the patient in this study was referred for SMAS or upper gastrointestinal obstruction. We excluded patients in who had any suspicious symptoms of SMAS. We excluded patients in whom there was a significant intraabdominal mass or para-aortic lymphadenopathy that could potentially distort the anatomy around the SMA and therefore the SMA angle. We also excluded those in whom there was insufficient contrast medium opacification of the mesenteric vessels to give accurate measurements, either intentionally (late portal phase imaging) or unintentionally due to inaccurate precise timing of the examination. In addition, we excluded those in whom there was free intraperitoneal or retroperitoneal fluid. We excluded patients with severe scoliosis.1.2 CT examination:Using PHILIPS Brilliance 64 row spiral CT scanner and PHILIPS Mx8000IDT 16 row spiral CT scanner. Select the 120kV conventional scanning tube voltage, tube current was 200-300mAs, Philips dynamic dose dispensing technology using controlled tube current (Dynamic Dose Modulation, DOM) automatically adjust the tube current, increase the signal in the thicker parts, in thinner or gas parts reducing signal, in the same circle process, according to the change of the same site in patients with different projection angles of absorption rate, real-time dynamic adjusting ray dose. Other conditions were the same scan groups (position:according to the condition of patients with upper limb artery choose the most comfortable position, lower extremity arterial the hands at the head of the supine position). Collimator combination:64* 0.625mm or 16* 0.75mm; scanning field:350mm; thickness:0.75 -2mm, reconstruction interval:0.5～1mm; pitch:0.65. Image acquisition is transmitted to Extended Brilliance Workspace workstation for postprocessing, the thickness of 5 mm,5 mm away from the layer. Contrast with Omnipaque 350mgI/ml, total 80ml, injection rate 3ml/s. After the injection of contrast agent 30s,50s for enhanced scan.1.3 Image analysis and data processing:1.3.1 Image reconstruction and data measurementThe area and included angle of the SMA-AO, the distance through the center of the pars horizontalis duodeni of the SMA-AO, and the distance of the origin of the SMA to the center of the pars horizontalis duodeni were measured through the sagittal MIP images (slice thickness 10mm) on the PHILIPS Extended Brilliance workstation. Data measured by two senior doctors on the same workstation respectively, taking their mean values. The difference between the obtained data from the two doctors is within 5%, if not, we must negotiate together and measure again.1.3.2 Statistical analysisStatistical analysis was performed using Student’s t-test and Pearson’s correlation coefficient at the 5% levelof significance level, using SPSS 19.0 for Windows. Draw the ROC curve of the area and included angle of the SMA-AO, the distance through the center of the pars horizontalis duodeni of the SMA-AO, and the distance of the origin of the SMA to the center of the pars horizontalis duodeni, find positive predictive value and calculate the true positive rate, false positive rate and accuracy of the positive predictive value.Results:2.1 Value of the area of the SMA-AO for the diagnosis of SMASStatistic data of the area and included angle of the SMA-AO, the distance through the center of the pars horizontalis duodeni of the SMA-AO, and the distance of the origin of the SMA to the center of the pars horizontalis duodeni of 24 SMAS cases and 42 cases non-SMAS are summarized. There are significant differences between the four indexes in the two groups (P<0.05), but no significant difference between the two groups of BMI (P<0.05). The Area under the roc curve of the area and included angle of the SMA-AO, the distance through the center of the pars horizontalis duodeni of the SMA-AO, and the distance of the origin of the SMA to the center of the pars horizontalis duodeni is 0.997,0.783,0.867 and 0.751. The positive predictive value of the area of the SMA-AO was 264 mm2, the false positive rate was 4.76%(2/42), the positive rate was 100%(24/24), and the accuracy rate was 96.97%(64/66). The positive predictive value of the included angle of the SMA-AO was 35.5°, the false positive rate was 45.24%(19/42), the positive rate was 87.50% (21/24), and the accuracy rate was 66.67%(44/66). The positive predictive value of the distance through the center of the pars horizontalis duodeni of the SMA-AO was 6.5 mm, the false positive rate was 23.81%(10/42), the positive rate was 83.33% (20/24), and the accuracy rate was 78.79%(52/66). The positive predictive value of the distance of the origin of the SMA to the center of the pars horizontalis duodeni was 46.5 mm, the false positive rate was 40.48%(17/42), the positive rate was 83.33%(20/24), and the accuracy rate was 68.18%(45/66).2.2 Correlation between SMA-AO and BMISpearman correlation analysis was performed by all the data in the SMAS group and non SMAS group, BMI was significantly positively correlated with the area of the SMA-AO (r=0.53, P<0.01), BMI was positively correlated with the angle of the SMA-AO (r=0.49, P<0.01), BMI was significantly positively correlated with the distance through the center of the pars horizontalis duodeni of the SMA-AO (r =0.63, P<0.01), BMI was not significantly correlated with the area of the SMA-AO (r=-0.12,P>0.01)Conclusion:The area of the SMA-AO can be used as a diagnostic standard for SMAS, because of its high accuracy in diagnosis for SMAS. There is a significant positive correlation between the area of the SMA-AO and BMI; BMI can be used as the basis for the screening of SMAS.