Acute primary superior mesenteric vein thrombosis is an acute intestinal vascular disorder of unknown etiology, with low incidence, high misdiagnosis rate and high mortality rate. Lack of characteristic clinical manifestations and signs in early stage, misdiagnosis rate is more than 95%, and untimely treatment can lead to extensive intestinal necrosis, diffuse peritonitis, shock, and even death, and the morbidity and mortality rate is 15%-50%. Acute superior mesenteric vein thrombosis is a very rare clinical disease with a total population incidence of about 1.8/100,000, accounting for 5%-15% of acute mesenteric diseases, often secondary to: (1) portal vein congestion and blood flow depression due to hepatic sclerosis or extrahepatic compression; (2) intra-abdominal septic infections, such as noma, ulcerative colitis, strangulated hernia, etc.; (3) certain blood abnormalities, such as (3) certain blood abnormalities, such as true erythrocytosis, hypercoagulability caused by oral contraceptives; (4) injuries caused by trauma or surgery, such as mesenteric hematoma, splenectomy, right hemicolectomy, etc. About 20-25% of these patients have an unknown cause, so it is called primary superior mesenteric vein thrombosis (APSMVT). The thrombus originates in the mesenteric arch vein and spreads proximally along the arch. Hemorrhagic infarction of the intestinal wall occurs when thrombus forms in the small rectal vein of the mesentery and in the vessels under the intestinal wall. Intraoperatively, the intestinal wall and the affected mesentery were obviously edematous and thickened, bruised plaques were seen in the mesentery, and new and old thrombi were seen in the lumen of the mesenteric veins. In the advanced stage of the disease, hemorrhagic infarction occurs in the entire intestinal wall, and there may be a large amount of bloody exudate in the abdominal cavity. Clinical manifestations The disease progresses relatively slowly, and the course of the disease is continuous and progressive. The boundary between the infarcted intestinal wall and the normal intestinal wall is characterized by a gradual transition. In the early stage of the disease, there are often non-specific prodromal symptoms for several days or even weeks, such as vague pain in the upper abdomen or around the umbilicus, abdominal distension, nausea, acidity, loss of appetite and other gastrointestinal symptoms. With the gradual spread and expansion of the thrombus, hemorrhagic infarction of the intestinal wall occurs, and the patient’s symptoms mostly worsen suddenly and persistently, but remain indefinitely localized, mostly accompanied by obvious abdominal distension, nausea, vomiting, and the use of general analgesic drugs is ineffective. The patient’s complaints of severe abdominal pain are not proportional to the milder abdominal signs. With the increase of thrombosis and vascular occlusion, extensive necrosis of the intestinal wall occurs, and the patient shows severe total abdominal pain with obvious abdominal distension, vomiting coffee-like liquid or dark red jam-like stool, and physical examination reveals high muscle tension, total abdominal pressure pain, rebound pain and other signs of peritoneal irritation, positive ascites sign, diminished or absent intestinal sounds, and turbid bloody fluid can be extracted by abdominal puncture, along with different degrees of Toxic shock symptoms. Preoperative diagnosis The early diagnosis of this disease is difficult, and the misdiagnosis rate of early diagnosis is 90-95% as reported abroad, and the disease is often in the necrotic stage or confirmed by intraoperative exploration by the time it is considered. The following symptoms can be used as a reference for early diagnosis: (1) anorexia and nausea without obvious reasons; (2) abdominal distension and vague abdominal pain with a tendency of persistent aggravation; (3) abdominal signs do not match the symptoms and there is no fixed pressure point; (4) bowel sounds can be hyperactive or diminished; (5) elevated white blood cell and platelet counts; (6) ineffective with general antispasmodic and analgesic drugs; (7) post-splenectomy is a predisposing factor for the disease The disease should be highly suspected at this time. Doppler ultrasonography may reveal dilated superior mesenteric veins, stagnant blood flow in the lumen, thrombosis, dilated intestinal canal, thickened intestinal wall, and fluid retention in the intestinal lumen; CT scan shows hyperdense mesenteric veins with ascites and thickened intestinal wall, and marked edema and hypertrophy of the mesentery. Sometimes dilatation and thrombosis of the superior mesenteric veins can be detected. The specific diagnostic significance of angiography in suspicious cases can be seen as follows: (1) signs of contrast reflux, contrast stagnation in the arterial arch or reflux into the artery; (2) spasticity of the superior mesenteric artery and its branches and thinning of the rectus artery; (3) prolongation of the arterial phase beyond 40 s; (4) slow filling of the mesenteric veins and venous visualization beyond 40 s; (5) thrombosis in the superior mesenteric veins; (6) failure to visualize the superior mesenteric veins or portal veins; (7) thrombosis in the superior mesenteric veins or portal veins. (7) prolonged contrast staining time in the affected intestinal segment, contrast in the intestinal canal, and thickening of the intestinal wall. The diagnostic rate is about 61%-93%. If blood turbid fluid is extracted by laparotomy, it indicates that there is intestinal strangulation and severe peritonitis, and surgical investigation should be performed as soon as possible. Treatment Intestinal resection is the most effective treatment, but there is no exact method to determine the extent of resected intestinal segments and mesentery during surgery. Commonly used methods such as covering with warm saline gauze or tethering are not very reliable, and postoperative thrombosis may still lead to intestinal necrosis or even anastomotic fistula. To completely remove the mesentery with venous thrombosis and the intestinal tube with purple color and poor temperature to touch, it is generally recommended to remove 15-20 cm from the affected intestine, and to see not only the arterial blood flow but also the absence of thrombosis in the veins for the preserved intestine and mesentery. Since the extent of intestinal necrosis and resection is not easy to determine in some patients, some scholars suggest that a second surgical exploration should be considered in the following cases: (1) no obvious boundary between the involved intestinal segment and normal intestinal segment at the first surgery; (2) extensive small intestinal ischemia without obvious necrotic area; (3) suspicious area in the remaining small intestine after resection of the diseased small intestine; (4) the exact type of intestinal ischemia is unclear and determined by postoperative imaging. In the above cases, anticoagulant drugs can also be injected after superior mesenteric vein dissection and embolization to observe intestinal changes, or the abdominal cavity can be temporarily closed for 24-48h for a second surgical exploration, which can significantly reduce the recurrence rate and mortality. There are different opinions whether to perform venous dissection for embolization during intestinal resection, and venous dissection for embolization is only effective for a few thromboses occurring in portal vein and main trunk of mesenteric vein, while most of the disease occurs in branches of mesenteric vein, and embolization is often ineffective and difficult to succeed. After surgery, low molecular weight heparin is routinely given subcutaneously for 7-10 days, while low molecular dextran, pansentin and salvia are given intravenously to thin the blood, reduce blood viscosity and prevent platelet aggregation. After oral diet, it is changed to warfarin or enteric aspirin and pentoxifylline for 3-6 months. Compared to regular heparin, low molecular weight heparin is more effective and has fewer side effects. Selective superior mesenteric arteriogram is feasible in cases where the auxiliary examinations suggest superior mesenteric vein thrombosis, but the peritoneal irritation signs are not severe and it is estimated that the intestinal canal is not yet necrotic or the above examinations do not suggest superior mesenteric vein thrombosis, but there is a high clinical suspicion. If the superior mesenteric vein and portal vein are found to be delayed, irregularly developed or even non-developed, the diagnosis can be made quickly and urokinase 200-300,000 U of thrombolysis can be injected through the catheter immediately, after which the catheter is left in the superior mesenteric artery and urokinase thrombolysis is given continuously at a dosage of 200-400,000 U per day. The patient should be closely monitored for changes in abdominal pain and signs. If the symptoms are not relieved within 6-8 hours but worsened and intestinal necrosis cannot be ruled out, the patient should be investigated by dissection immediately. Prognosis Because of the difficulty of early diagnosis of this disease, the mortality rate is high, and the mortality rate without surgical treatment is 90%-100%. The mortality rate is 35% in the group of intestinal resection alone, and significantly decreases to 23% in the group of intestinal resection plus postoperative anticoagulation, with a lower mortality rate in primary than secondary cases. In summary, due to the lack of specificity of the symptoms of this disease, early diagnosis is difficult, and Doppler ultrasound, spiral CT or mesenteric angiography should be applied to further clarify the diagnosis when the disease is highly suspected. Interventional thrombolytic therapy can be tried in the early stage of the lesion, and if the symptoms do not relieve or worsen and the signs of peritoneal irritation appear, timely surgical investigation should be performed, and if necessary, secondary surgical investigation is required. At the same time, the correct use of anticoagulant drugs after surgery is the key to prevent the recurrence of thrombosis and improve the cure rate.