Let’s start with a case: young female, 24 years old, admitted to the hospital with postprandial epigastric pain and vomiting for 2 months. The patient presented 2 months ago with postprandial epigastric pain with nausea and vomiting, and the vomit was food and bile without obvious blood staining. The symptoms were relieved when the patient was lying on the left side. In the past six months, the patient took “diet tea” and lost 6 kg; in the past three months, her menstruation was irregular. At the time of admission, she weighed 44 kg, with a body mass index (BMI) of 17, a thin body type, and a flat and soft abdomen without obvious pressure or mass. Blood tests showed hemoglobin 98 g/L and albumin 32 g/L. Upper gastrointestinal imaging showed interruption of the horizontal segment of duodenum; gastroduodenoscopy suggested external pressure stenosis of the horizontal segment of duodenum. Abdominal CT reconstruction showed that the angle of the superior mesenteric artery was 14°, compressing the horizontal segment of duodenum. The diagnosis of benign duodenal stasis was made. The patient was given an endoscopic nasal to gastrojejunal double-lumen tube and adequate enteral nutritional support for one month, with a weight gain of 3.5 kg, and tolerated oral feeding after removal of the double-lumen tube. There is a large artery in the abdomen, called the abdominal aorta, which has many branches to supply blood to the abdominal organs. One of these branches is called the superior mesenteric artery (SMA), which supplies blood to all of the small intestine and half of the large intestine. the SMA is at an acute angle to the abdominal aorta, with the left renal vein and the horizontal segment of the duodenum (duodenal segment 3) passing within the angle. In normal individuals, the SMA root is supported by adipose tissue and lymphatic tissue between the SMA and the abdominal aorta, maintaining this angle at approximately 35-60°, allowing the left renal vein and the horizontal segment of the duodenum to remain open. CT reconstruction and vascular ultrasound can be used to measure the angle and visualize the compression of the left renal vein and the duodenal segment. When left renal vein compression leads to left renal vein hypertension, it is called nutcracker phenomenon (or left renal vein compression syndrome), which may manifest as varying degrees of hematuria, some patients may even have secondary anemia, and some patients may develop proteinuria, renal insufficiency, etc. Male patients may also develop left spermatic varicose veins. The hematuria caused by this disease is related to the position: it is heavier during the day when the patient is in the standing position, and it can be significantly reduced at night when the patient is in the lying position. Comparing the degree of hematuria during the day and at night helps to differentiate it from hematuria due to other renal diseases. When compression of the horizontal segment of the duodenum leads to upper gastrointestinal obstruction called benign duodenal stasis (or superior mesenteric artery syndrome, Wilkie’s syndrome), the manifestation is mainly postprandial bloating with vomiting of gastric contents and bile because food cannot pass through the duodenum to the jejunum; the symptoms may be partially relieved when the pressure of the SMA on the duodenum is reduced in the recumbent position. Further weight loss can occur due to the inability of food to enter the small intestine for digestion and absorption as a result of the disease. The examination of the disease is as described in the previous cases. Both of these diseases can also occur in the same patient due to the same pathogenesis. Treatment: Patients with milder symptoms of adolescent nutcracker phenomenon can be temporarily observed or given nutritional support, and symptoms will improve with growth or improved nutrition, increased visceral fat, and greater angle between SMA and abdominal aorta; more severe symptoms require placement of renal vein stents or surgical treatment. Benign duodenal stasis can also be treated with nutritional support, but duodenal stasis can prevent food from passing down the duodenum, so a jejunal nutrition tube is often placed to provide enteral nutrition across the obstruction site. directly into the small intestine. Etiology: The cause of both benign duodenal stasis and nutcracker phenomenon is the small angle between the SMA and the abdominal aorta, which in turn mainly results from the loss of visceral fat, so it is common in young people with rapid growth, long and lean body size, and in adults who have lost significant weight for various reasons (disease, trauma, psychological factors, etc.). Patients with spinal cord trauma or spinal surgery are also prone to this pinch angle hyperextension, which is considered to be related to neuromuscular factors or lumbar hyperextension; some other patients may have congenital anomalies of vascular anatomy. Therefore, these two diseases are not solely related to wasting and visceral fat loss, but wasting and rapid weight loss are indeed their most important risk factors. China is currently undergoing a transition from poor to rich, and on the one hand, the number of obese people is increasing, while on the other hand, wasting due to various reasons is still widespread. One of the manifestations of the deteriorating physique of Chinese university students, as reported in the media, is that boys are getting fatter and girls are getting thinner. It is very common for women on university campuses and among young white-collar workers not to lose weight properly. In this regard, there are 3 points to remind girls: 1, not only to weight or body mass index on fat and thin, to combine lean body mass index and fat rate comprehensive judgment (see my long microblogging about human body composition analysis); 2, if you look at weight alone, should not be less than 18 BMI as the bottom line, never lose too much weight; 3, on the view of most men I know, women still need to have meat to be sexy enough.