Congenital absence, atresia, and stenosis of the duodenum

　　Starting from the 5th week of embryonic development, the endodermal epithelial cells in the gut tube cavity overproliferate, causing the intestinal cavity to become occluded, resulting in a temporary filling period. By the 9th to 11th week, the epithelial cells undergo a process of cavitation, forming many vesicles. Subsequently, the vesicles fuse together, marking the cavitation period, which reopens the intestinal cavity, forming a normal intestinal tube by the 12th week. If the formation of vesicles is obstructed, remaining in the filling period, or if the vesicles do not fully fuse, the recavitation of the intestinal tube is impaired, leading to intestinal atresia or stenosis. This is the main etiology of duodenal atresia (Tandler's theory), which often accompanies other malformations, such as Down syndrome (30%), malrotation of the intestines (20%), annular pancreas, esophageal atresia, and malformations of the anus, rectum, cardiovascular system, and urinary system. The coexistence of multiple system malformations suggests a relationship with systemic developmental defects in the early embryonic stage, rather than simply due to local maldevelopment of the duodenum. Some believe that impaired blood supply to the intestinal tube during embryonic development, with ischemia, necrosis, absorption, and abnormal repair, can also lead to duodenal atresia or stenosis.

　　The lesion is mostly located in the second segment of the duodenum, with obstruction occurring mostly at the distal end of the ampulla, and a few at the proximal end. Common types include:

　　1, Diaphragm type:The外形 of the intestinal tract remains continuous, with an intact diaphragm in the intestinal lumen, usually single, but can also exist in multiple locations simultaneously; or the diaphragm is a membrane-like web, prolapsing towards the distal obstruction site to form a bag-like shape; or there is a needle-like small hole in the center of the diaphragm, making it difficult for food to pass through. The ampulla is often located at the posterior medial or near and far sides of the diaphragm.

　　2, Blind segment type:The continuity of the intestinal tract is interrupted, with the two blind ends completely separated, or only connected by fibrous bands, and there is also a cleft defect in the mesentery. This type is rare in clinical practice.

　　3, Duodenal stenosis:There is a circumferential hyperplasia in the intestinal lumen mucosa, where the intestinal tract has no dilating function; there is also a narrow segment near the ampulla.

　　The duodenum and stomach near the obstruction are obviously dilated, with thickened muscular layer, degeneration of the intestinal submucosal plexus, and poor peristaltic function. In cases of intestinal atresia, the distal intestinal tract becomes atrophic and thin, and there is no gas in the intestinal lumen. In cases of intestinal stenosis, there is air in the distal intestinal lumen.

　　Due to severe vomiting, there are complications such as significant dehydration, acid-base imbalance, electrolyte disorder, weight loss, and malnutrition.

　　1, Dehydration:Sodium salts (NaCl, NaHCO3) are the main inorganic salts that determine the osmotic pressure of extracellular fluid, and therefore, serum sodium concentration is the main factor determining the level of plasma osmotic pressure. Due to the different proportions of water and sodium loss, it leads to different changes in plasma sodium concentration and osmotic pressure. During dehydration, the clinical practice often divides dehydration into three types based on the level of serum sodium concentration: isotonic dehydration, hyposmotic dehydration, and hyperosmotic dehydration.

　　2, Electrolyte disorder:Water and electrolytes are widely distributed both inside and outside of cells, participating in many important functions and metabolic activities within the body, and play a very important role in maintaining normal life activities. The dynamic balance of water and electrolytes in the body is achieved through the regulation of the nervous and humoral systems. Common water and electrolyte metabolic disorders in clinical practice include hyperosmotic dehydration, hyposmotic dehydration, isosmotic dehydration, edema, water intoxication, hypokalemia, and hyperkalemia.

　　X-ray erect anteroposterior flat film examination can be performed, showing a large liquid plane in the upper left abdomen, and also a liquid plane in the upper right abdomen. This is the dilated stomach and the proximal duodenum, with no gas in other parts of the abdomen, forming a 'double bubble sign'. This is a typical X-ray sign of duodenal atresia. The flat film of duodenal stenosis is similar to atresia, but the proximal duodenal dilation is less, the liquid plane is slightly smaller, and a small amount of gas can be seen in the rest of the abdomen. In cases of neonatal intestinal obstruction, it is禁忌 to perform barium meal examination, which can cause fatal aspiration pneumonia of barium liquid. Sometimes, to distinguish from malrotation of the intestines, barium enema can be performed to observe the position of the cecum and ascending colon. However, in fact, it is not necessary, as the findings of abdominal flat film can already confirm the diagnosis. In older children with atypical history and symptoms of partial duodenal obstruction, a barium swallow examination can be performed, and the barium should be aspirated after the examination.

　　In recent years, the use of prenatal ultrasonography has detected two fluid masses in the abdominal cavity, which have certain diagnostic value and can provide a basis for early surgery after birth.

　　In cases of duodenal atresia, pregnant women in the early stages of pregnancy may have phenomena such as viral infection, vaginal bleeding, and often polyhydramnios. The baby may start to vomit frequently within a few hours after birth, with a large amount of vomit containing bile. If the obstruction is near the ampulla, bile is not present. There is no normal meconium excretion, or only a small amount of white mucus or greasy-like material may be excreted, but there may also be 1-2 episodes of small gray-green feces. The symptoms in cases of severe stenosis are similar to those of atresia. In cases with mild stenosis, intermittent vomiting may appear a few weeks or months after birth, or even start vomiting years later. Since it is a high-position obstruction, there is generally no abdominal distension, or only mild upper abdominal bulging, and gastric peristalsis waves are rare. Due to severe vomiting, there are obvious dehydration, acid-base imbalance, electrolyte disorder, weight loss, and malnutrition.

　　Disorders in the embryonic development process of the duodenum can lead to atresia or stenosis of the duodenal segment. There are no particularly effective preventive measures for this disease, and early detection and treatment are the key to prevention and treatment.

　　X-ray erect anteroposterior flat film examination can be performed, showing a large liquid plane in the upper left abdomen, and also a liquid plane in the upper right abdomen. This is the dilated stomach and the proximal duodenum, with no gas in other parts of the abdomen, forming a 'double bubble sign'. This is a typical X-ray sign of duodenal atresia. The flat film of duodenal stenosis is similar to atresia, but the proximal duodenal dilation is less, the liquid plane is slightly smaller, and a small amount of gas can be seen in the rest of the abdomen. In cases of neonatal intestinal obstruction, it is禁忌 to perform barium meal examination, which can cause fatal aspiration pneumonia of barium liquid. Sometimes, to distinguish from malrotation of the intestines, barium enema can be performed to observe the position of the cecum and ascending colon. However, in fact, it is not necessary, as the findings of abdominal flat film can already confirm the diagnosis.

　　Immediately infuse nutrient fluids after surgery to promote recovery. Avoid spicy foods such as cigarettes, alcohol, coffee, strong tea, and various spicy seasonings such as scallions, ginger, garlic, chili, pepper, curry, etc.

　　Nasogastric tube decompression should be placed before surgery to correct dehydration and electrolyte imbalance, appropriately supplement blood volume, keep warm, and provide vitamin K and antibiotics.

　　During the operation, it is necessary to carefully examine for other congenital malformations, such as malrotation of the intestines and annular pancreas. The distal end of the atresia needs to be injected with normal saline to expand it, and the entire small intestine needs to be checked in order for multiple atresia and stenosis. The operation method is selected according to the malformation situation, with diaphragm-type atresia using diaphragm resection, and care must be taken to prevent injury to the entrance of the common bile duct during resection. If the proximal and distal ends of the duodenum are very close or there is annular pancreas at the same time, duodenoduodenal anastomosis can be performed. For duodenal atresia and stenosis at the distal end, duodenal-jejunal anastomosis can be chosen, but it may produce blind-end syndrome after surgery. It can also be used to trim the duodenum, reshape and anastomose the expanded intestinal tract by trimming, which can restore the effective peristalsis of the duodenum early, advance the date of eating, and reduce complications.

　　Some advocate that gastrostomy can ensure gastric emptying, prevent aspiration, and can lead the gastric tube through the anastomosis into the jejunum for early feeding. It is also possible to place a catheter in the jejunum and immediately infuse nutrient fluids after surgery to promote recovery.

　　The treatment of duodenal atresia is quite difficult, and the efficacy is still not satisfactory. The mortality rate is about 50%, and the prognosis is related to factors such as the time of diagnosis, the degree of malformation, multiple atresia, severe combined malformation, premature infants, or low birth weight infants.