The mesentery consists of the wall layer and the dirty peritoneum, mainly the small intestinal mesentery and the colonic mesentery, in addition to the appendicular mesentery and the ovarian and fallopian tube mesentery. The small intestinal mesentery is the peritoneum connecting the jejunum, ileum and posterior abdominal wall, and is fan-shaped. The part attached to the posterior abdominal wall is called the mesenteric root, and the small intestinal margin of the mesentery is 6-7 m long, containing the superior mesenteric arteries and veins and their branches, celiac ducts, nerve plexus and lymph nodes. Then abdominal pain appears, mostly in the right lower abdomen and around the umbilicus, often paroxysmal, like writhing. After eating, the pain reappears and food may be vomited. On examination, facial flushing, pale lips, congestion in the pharynx, abdominal pressure pain is mostly distributed obliquely from the lower right to the upper left, but it is obvious in the right lower abdomen, without muscle tension and rebound pain. In thin children, enlarged lymph nodes can sometimes be palpated. Clinically, it must be differentiated from acute appendicitis. The former is usually fever followed by abdominal pain, metastatic abdominal pain is not obvious, abdominal pain is often not limited, and elevated white blood cell count is not obvious; the latter mostly has metastatic right lower abdominal pain, which is persistent, nausea and vomiting are more obvious, right lower abdominal pressure pain is limited and fixed, often accompanied by abdominal muscle tension and rebound pain, and white blood cell count is often significantly elevated. In typical cases, it is generally not difficult to identify. However, in young children who are not very cooperative or unable to express their condition, identification may be difficult. Etiology The pathogenic microorganisms responsible for nonspecific mesenteric lymphadenitis may include Staphylococcus spp (Staphylococcus aureus), Streptococcus hemolyticus, Streptococcus erythropolis, Mycobacterium pseudotuberculosis, Penicillium spp, viruses, Schistosoma haematobium, and amoebae. The exact etiology of this disease is not known. It is common in children or adolescents and is most often seen in the ileocecal lymph nodes. There are many lymph nodes in this area, and they are particularly abundant in children. The longer residence time of the intestinal contents in the distal ileum allows for the absorption of toxins and bacterial products in this area and causes an acute inflammatory response in the lymph nodes. It is also believed that patients often feel tired, unwell and have symptoms of inflammation in the upper respiratory tract 1 to 2 days before the onset of the disease, so it is thought to be due to bloodstream infection by streptococci. Some authors have suggested that toxemia is the key to the development of mesenteric lymphadenitis, but lymph node cultures are mostly free of bacterial growth. Acute mesenteric lymphadenitis is most often seen in children under 7 years of age. The onset of the disease is often preceded by prodromal symptoms such as sore throat, fever, and malaise before the onset of umbilical and right lower abdominal pain, nausea, vomiting, and sometimes diarrhea or constipation. This pathogenesis is the opposite of acute appendicitis in which abdominal pain is followed by fever, and the body temperature rises suddenly at the early stage of the disease. On physical examination, there can be pressure pain in the umbilicus and right lower abdomen, which is more extensive and the pressure pain points are not fixed. Because of the underdeveloped abdominal muscles in children, abdominal muscle tension may not be obvious. Sometimes small nodule-like masses can be found. The white blood cell count is elevated or normal. In the case of streptococci, a thin, grass-green fluid may be obtained by laparotomy and Gram-positive cocci may be found on smear. Physiology Pathogenic microorganisms causing nonspecific mesenteric lymphadenitis may include Staphylococcus spp. (Staphylococcus aureus), Streptococcus haemolyticus, Streptococcus erythropolis, Mycobacterium pseudotuberculosis, Penicillium spp., viruses, Schistosoma haematobium, and amoebae. The exact cause of this disease is not known. It is often seen in children or adolescents, and most often in the ileal lymph nodes. There are many lymph nodes in this area, and they are particularly abundant in children. The intestinal contents remain in the distal ileum for a long time, and toxins and bacterial products are easily absorbed there, causing an acute inflammatory response in the lymph nodes. It is thought to be due to bloodstream infection by streptococci, but it is also thought to be related to intestinal inflammation and parasitism. It is most often seen at the end of the ileum. The lymph nodes show multiple congestion and enlargement. A small amount of inflammatory exudate may be present in the abdominal cavity. Microscopically, the lymph sinuses are seen to be dilated and neutrophils enter the lymph sinuses by small vessels and phagocytose bacteria. Some leukocytes may undergo degenerative collapse as a result, forming cellular debris or denatured material. The blood vessels in the lymph nodes are also dilated and congested, with hyperplasia of the germinal centers and proliferation of sinus cells and immunoblasts. It has also been suggested that the patient often feels lethargy, discomfort and symptoms of inflammation of the upper respiratory tract 1 to 2 days before the onset of the disease, so it is thought to be due to bloodstream infection by streptococci. Some authors believe that toxemia is the key to the development of mesenteric lymphadenitis, but lymph node cultures are mostly devoid of bacterial growth. It is rare clinically and can occur at any age, but is mainly seen in children and adolescents and is an important cause of acute abdominal pain in young children. Diagnosis 1. History The disease is often preceded by a history of upper respiratory tract infection, intestinal infection, and cervical lymphadenitis. 2, symptoms are similar to acute appendicitis. The main manifestation is abdominal pain, which can occur in any part of the abdomen, with the right lower abdomen being the most common. Occasionally, the pain is metastatic right lower abdominal pain, which is vague or spasmodic in nature, mild and mostly tolerable. Between episodes of pain, the patient may have no other discomfort, and some patients may have nausea, vomiting, diarrhea or constipation. There is fever at the beginning of the disease, and the temperature usually does not exceed 39°C. The disease can be recurrent, but is mostly self-limiting. 3.Signs facial flushing, pale lips, and congestion in the throat. Abdominal pressure pain, mostly from the lower right to the upper left in an oblique distribution, but the right lower abdomen is obvious; the right lower abdomen can have different degrees of pressure pain, the pressure pain point is often in the medial side or above the McDonald’s point, and the location of pressure pain is not consistent in each examination, and there is rarely muscle tension and rebound pain. Occasionally, small nodule-like lymph nodes can be palpated in the right lower abdomen, with pressure pain. Laboratory tests: peripheral blood leukocyte count is usually normal or slightly increased or decreased, while the proportion of lymphocytes is increased. Other auxiliary examinations: high-frequency ultrasound can visualize the abdominal muscles, large blood vessels, peristalsis of intestinal tubes and the size, morphology, echogenicity and distribution of enlarged lymph nodes on the mesentery, which is convenient and easy to perform without radiation damage. High-frequency ultrasound imaging of mesenteric lymphadenitis can make qualitative diagnosis based on the increase in the number of mesenteric lymph nodes, the increase in the diameter, and the presence of abnormalities in the dermal echogenicity, longitudinal, transverse, and oblique scans, combined with respiratory movements and acoustic imaging of the digestive tract. The disease should be differentiated from the following lesions: 1. Tuberculous mesenteric lymphadenitis is most commonly seen in children and adolescents. The sonograms are oval hypoechoic, isoechoic, mixed echogenic, with some strong echogenic foci of fusion, liquefaction and calcification, or combined with a large amount of ascites, intestinal adhesions and other changes. 2. Mesenteric malignant lymphoma is a common source of mesenteric or retroperitoneal lymphoma, usually involving multiple sites, with a tendency to be round, with an aspect ratio of <2, involving long segments, and may have central necrosis in the form of strong echogenic spots, or multiple nodules aggregated into a petal shape. However, the sonogram cannot be completely relied on, and considering the immature development of mesenteric lymph nodes in children, there are some differences in the sonogram, which should be further discussed. Differential diagnosis This disease is easily confused with acute appendicitis. Patients usually have fever followed by abdominal pain, metastatic abdominal pain is not obvious, abdominal pain is often not limited and not fixed, and elevated white blood cell count is not obvious; the latter mostly has metastatic right lower abdominal pain that is persistent. Nausea and vomiting are more obvious, and the right lower abdominal pressure pain is limited and fixed, often accompanied by abdominal muscle tension and rebound pain. The white blood cell count is mostly significantly elevated. In addition, the disease should be differentiated from intestinal tumors, ovarian tumors, tuberculous lymphadenitis, Crohn's disease, Yersinia enterocolitica and Yersinia lymphadenitis. Acute mesenteric lymphadenitis and acute appendicitis in children have many similarities, both can manifest as right lower abdominal pain, fever, etc., and are easily misdiagnosed, but each has its own characteristics. Treatment Non-surgical treatment Antibiotic therapy is the mainstay 1. Acute mesenteric lymphadenitis should not be treated surgically and should be treated with anti-infective therapy. Treatment is conservative, according to ampicillin 0, 1g/(kg/d) plus 0, 9% saline, twice daily intravenous drip, combined with metronidazole once daily intravenous drip. For patients with fever and abdominal pain, dexamethasone 5mg/time was added, and dexamethasone was administered for no more than 3 days. 2 days later, there was a significant decrease in leukocytes and significant relief of symptoms, and the treatment was continued for 1 week. After 2-3 days of treatment, most of the fever subsided, leukocytes decreased significantly, and abdominal pain symptoms were significantly relieved, and most of them were discharged after 1 week of anti-infection treatment. The B-ultrasound examination is directly based on the image of the appendix and can also show the enlarged lymph nodes, which is an effective way to differentiate between the two. If the disease is still stable or the onset is within 6h, observation can be continued. Acute appendicitis is often progressively worse and should be operated; acute mesenteric lymphadenitis can often be relieved. If the condition is severe or the onset of acute appendicitis cannot be ruled out for more than 12h, a dissection should be performed and appendectomy should be performed. If the abdominal pain persists for 6h with anti-infection treatment, the body temperature does not drop and the abdominal muscle is more tense than before, surgery should be performed decisively to avoid appendiceal perforation, and the observation time should not exceed 24h. If the abdominal pain is not severe after treatment, the body temperature does not increase significantly and the blood leukocytes do not continue to increase, the disease can be treated as such and the observation time can be extended to avoid unnecessary surgical trauma. In case of misdiagnosis of acute appendicitis for surgery, it is generally accepted that there is no excuse. Delayed surgery for acute appendicitis can result in perforation and peritonitis, and may even be life-threatening. If the mesenteric lymph nodes in the ileocecal region are found to be enlarged and congested intraoperatively, the enlarged lymph nodes should be removed for pathological biopsy. Complications Complications: Because of the paroxysmal abdominal pain, such as wringing, complications such as vomiting again after eating appear clinically. Prognosis: The disease has a good prognosis and often resolves spontaneously within 3 to 4 days. Prevention: In the presence of fever, especially in children and young adults, any prodromal symptoms of upper respiratory tract infection should be treated immediately with antiviral and anti-infective therapy to prevent the occurrence of acute nonspecific mesenteric lymphadenitis.