After nearly half a century of painstaking exploration, people have gained a preliminary understanding of the function of the spleen. From the uselessness of the spleen to the rise of spleen-preserving surgery to today’s elective spleen-preserving surgery, spleen surgery in China has made great progress, and the modern concept of spleen surgery has been accepted by most scholars. Nevertheless, our understanding of the function of this mysterious organ is still scarce, and there are still many controversies in splenic surgery that remain unresolved. Continuously exploring and correctly recognizing the function of the spleen in physiological and pathological states will help to resolve the controversies, so that the best treatment can be adopted for different situations and splenic surgery can be carried out rationally. I. OPSI opens the door to the study of spleen function The principle of treatment of traumatic spleen reflects the development process of people’s understanding of spleen function. The famous surgeon Kocher once proposed in 1911: there is no harm to the organism after splenectomy, and the spleen should be removed when it is injured. This was mainly due to the fact that there was less research on the function of the spleen at that time, and it was considered harmless to cut it, which made total splenectomy become the “gold standard” for the treatment of splenic trauma, and continued until the middle of the 20th century. 1952, King and Schumacker reported the post-splenectomy suspicious infection (OPSI) for the first time, which made people attention and exploration of splenic function, and that splenectomy was not harmless. Studies have shown that Streptococcus pneumoniae infections account for approximately 80% of OPSIs, and Gram-negative bacillus infections are also gaining attention [1]. Bacterial infection and concomitant toxin uptake stimulate a cascade reaction by promoting the release of inflammatory mediators and cytokines (e.g., IL-6, TNF-α, platelet-activating factor, oxygen free radicals, etc.), resulting in extensive endothelial damage and leukocyte exudation and aggregation, which is the basis for severe sepsis and multiorgan insufficiency. Bacterial clearance by the spleen is mainly accomplished by intrasplenic macrophages, while IL-1 and granulocyte colony-stimulating factor (G-CSF) produced by the spleen can enhance phagocytosis by alveolar macrophages, and G-CSF also antagonizes the damaging effects of gram-negative bacterial lipopolysaccharide (LPS) on the organism by inhibiting the release of TNF-α [2]. Nowadays, it is recognized that the spleen has a powerful immune function in addition to its hematopoietic, storage, filtration, and destruction functions. The discovery of pro-phagocytic peptides not only provides strong evidence for the spleen’s anti-infective immune function, but also indicates that the spleen has an endocrine function. Although the spleen has many important functions, it is not like the heart, liver, kidneys and other organs that are essential to life. Therefore, in clinical work, traumatic injuries of the spleen should follow the principle of “saving life first, preserving the spleen second”, and should not cut the spleen at will, nor blindly preserve the spleen, and preserve the spleen should be appropriate according to the time, the place and the person. The spleen should be preserved “according to the time, the place and the person”. Otherwise, the one-sided pursuit of preserving the spleen will often run counter to one’s wishes, and may even lead to serious consequences. In short, according to the time, the severity of the spleen injury, the time of consultation and the patient’s systemic status, such as the severity of the spleen injury, the late consultation, the patient’s state of shock or the combination of serious injuries to other organs, it is necessary to seize the main contradiction, as far as possible, to deal with the injury or even to remove the spleen, to control the hemorrhage, to create the conditions for the resuscitation and other important operations, and should not be pursuing the preservation of the spleen to cause a tragedy;. According to the local medical conditions and facilities, whether the local medical conditions and facilities have the technology and equipment to comprehensively assess the degree of splenic injury and splenic function, such as computed tomography (CT), single photon emission computed tomography (SPECT), bedside color ultrasound, etc., and whether they are able to complete the close monitoring of spleen preservation treatment and the emergency treatment of emergencies; According to the people, it mainly refers to the operator’s technical level and experience, and his ability to adopt appropriate treatment strategies according to the condition. The ability to adopt appropriate treatment strategies according to the patient’s condition. All three are complementary and indispensable. The treatment of clinical splenic trauma should refer to the grading standard of splenic injury proposed by the 6th National Conference on Splenic Surgery in 2000, and when there are conditions for spleen preservation, one or a combination of several methods should be chosen according to the condition of the injury in order to preserve part or all of the structure and function of the spleen. Avoiding medical splenic injury and innocent splenectomy Although the spleen is not necessary for maintaining life, the prevention of medical splenic injury should not be neglected. Surgery on organs adjacent to the spleen should always be vigilant to avoid accidental injury and resection of the spleen. When the operator’s technical experience and local conditions permit, the spleen should be carefully freed from adhesion with adjacent organs or tissues, and the normal spleen should be preserved as far as possible. The reasons for this include the following: first, we currently know very little about the function of the spleen, and it is not entirely clear what adverse effects, especially long-term effects, the removal of a normal spleen will have on the organism; second, it is now clear that individuals with total splenectomy are susceptible to serious infections, especially in children who have a higher incidence of OPSI, and once this occurs, the morbidity and mortality rates are extremely high; third, medical splenic injuries and innocuous splenectomy are contrary to the minimally invasive concept and ethical conduct of surgeons. Therefore, we hope that surgeons will update their concepts, deepen their understanding, and raise their vigilance, so that they can fully reveal the operation field, strictly abide by the operation specifications, operate gently and carefully, and not be careless, so that they can eliminate medically caused splenic injuries as much as possible. In practice, if the spleen is inadvertently injured, the general principle of treatment is that children should give priority to the preservation of the spleen, in order to reduce the incidence of serious infections in the future, and at the same time, due to the relatively large proportion of connective tissue in children’s spleens, the success rate of the preservation of the spleen is relatively high. Elderly people need to be treated with caution because as they age, the elastin in the spleen decreases and the peritoneum becomes thinner, making it more difficult to preserve the spleen. In addition, the cardiorespiratory function of the elderly decreases, so failure of spleen preservation will be very difficult to deal with, and will easily lead to prolonged hospitalization and an increase in the morbidity and mortality rate. It is worth thinking about how to weigh the risks and benefits, and it is fundamental to avoid medical injury to the spleen. Currently, there are many controversies about whether to cut or preserve the spleen in the treatment of gastric cancer, pancreatic caudal lesions and portal hypertension. The controversy mainly focuses on whether it affects the curative effect of the primary disease, what function the spleen plays in the above cases, and what the long-term effect of splenectomy/preservation is, etc. More in-depth research is needed. In the treatment of gastric cancer, some scholars advocate extended radical surgery based on the principle of “cutting the tumor to the end”, which makes it inevitable to remove the spleen in many cases. Some scholars believe that the spleen has important anti-infection and anti-tumor immune functions, and strongly advocate spleen-preserving radical surgery for gastric cancer. There is no lack of evidence to support both views, and more prospective randomized controlled studies are needed to answer the question of which is better or worse. With deeper research on tumor pathogenesis, it is now recognized that some malignant tumors are systemic diseases, as evidenced by the shift in treatment strategies for breast cancer. So, does surgical enlargement for gastric cancer always improve prognosis? A prospective randomized controlled study [3] demonstrated that combined splenectomy or pancreatectomy increased the rate of postoperative complications and in-hospital mortality in radical D2 surgery, while long-term survival was not improved. [4] Long-term follow-up of 126 gastric cancer patients after radical resection found that the spleen-preserving group had a significantly better recurrence rate (26.8%) and overall morbidity and mortality rate (41.4%) than the splenectomy group (67.2% and 71.6%, respectively). Similar conclusions were obtained in several other studies [5-7], i.e., the complication rate, recurrence rate, and morbidity and mortality rate of radical gastric cancer surgery with spleen preservation were lower than those of the splenectomy group. With the advancement of surgical techniques, complete removal of the splenic hilar and parasplenic artery lymph nodes while preserving the spleen has become possible, and it does not affect the radicality of surgery in most cases. As to whether the spleens of gastric cancer patients have anti-tumor immune hypofunction or negative anti-tumor immune function, and how to judge the bi-directionality and temporal phasing of the spleen’s anti-tumor immunity in specific cases, there is no scientific quantitative standard yet. Therefore, we believe that the indications for combined splenectomy in gastric cancer surgery are: the tumor has invaded or metastasized to the spleen, and there are splenic hilar lymph node enlargement and fusion that are difficult to be completely removed. Otherwise, spleen-preserving surgery can be considered appropriately according to the conditions. The words “according to the conditions” and “appropriate” mean that it should be performed according to the patient’s state and local conditions, and the operator’s technical level, and it will bring more trauma and poorer outcome to the patient if the spleen preservation is purely pursued with excessive prolongation of anesthesia, operation time, and large amount of blood loss and fluid loss, and even affecting the radical nature of the tumor. The patient will be more traumatized and have a poorer prognosis, which will do more harm than good. Spleen preservation is recommended for benign pancreatic body-caudal lesions. The main indications for spleen-preserving pancreatic body-caudal resection are: trauma to the pancreatic body-caudal region, pancreatic endocrine tumors, pancreatic cysts, pancreatic cystadenomas, chronic pancreatitis, and neonatal islet cell proliferation. In addition, early-stage cancers confined to the tail of the pancreatic body that do not infiltrate the spleen and the pancreatic parenchyma is not tightly adherent to the spleen may be attempted to preserve the spleen. Although splenectomy has been reported to have a negative impact on the long-term outcome of malignant tumors in the tail of the pancreatic body [8], and clinically, due to the difficulty of early detection of malignant tumors in the tail of the pancreatic body, which are mostly in advanced stages at the time of consultation, preservation of the spleen is feared to be difficult to achieve. When the nature of the tumor cannot be identified intraoperatively, frozen section can be used to clarify the nature of the tumor, and if it still cannot be determined, resection of the spleen is recommended to eliminate the future problems. Pancreatic coccygectomy with preservation of splenic vessels should be preferred among spleen-preserving surgical procedures because it is close to the physiology and can maximize the preservation of the spleen’s blood filtration function and bacterial contouring function. If there is difficulty in preserving the splenic vessels, the splenic vessels can also be cut off before the branches of the splenic vessels (gastric short vessels, gastric posterior vessels, gastric omental left vessels), and the spleen will not be necrotic because of sufficient collateral circulation, but the spleen should be checked again for ischemic signs before closing the abdomen, so as to avoid the occurrence of splenic infarction in the postoperative period. Nowadays, laparoscopic technology is developing rapidly, and laparoscopic pancreatic body-caudal resection with preservation of the spleen is increasingly reported, which is mainly used for benign pancreatic body-caudal lesions, and the results are good if the cases can be selected appropriately [9]. Regarding the retention of the spleen in portal hypertension, there have been many debates, mainly involving: how the spleen immune function in portal hypertension; how retaining the spleen affects hepatic fibrosis; and whether the residual spleen will become enlarged and hyperfunctional again. Some domestic scholars have shown that the proliferation of lymphocytes in the enlarged spleen of portal hypertension is enhanced, and the spleen still retains a certain immune function at this time.The experimental study of Akahoshi et al[10] confirmed that the spleen secretes a large amount of TGF-β in the rat cirrhosis model, which plays a role in accelerating the progression of liver cirrhosis. Other cytokines associated with the spleen’s promotion of liver fibrosis include endothelin, IL-6, and TNF-α. There is no clear evidence as to whether the spleen plays only a negative role in the progression of cirrhosis. There are various weaning and shunting procedures available for the surgical treatment of portal hypertension. In foreign countries, there are those who use Warren’s operation, i.e. distal splenorenal vein shunt, which not only relieves portal hypertension, but also preserves the function of the spleen, and the effect is ideal. Post-hepatitis cirrhosis in China is often combined with severe splenomegaly and hypersplenism, and it is difficult to completely correct hypersplenism by simply performing Warren operation. In China, there are studies on the treatment of portal hypertension by performing splenic artery narrowing distal splenorenal shunt with good results, but due to the small number of reported cases and the short observation time, long-term follow-up observation with a large sample is needed. After 26 years of observation, it was confirmed that autologous splenic tissue transplantation combined with esophageal transverse anastomosis after partial splenectomy was highly effective in the long-term treatment of portal hypertension, with good splenic immune function without aggravation of hepatic fibrosis. They concluded that preserving the splenic pedicle, transplanting part of the spleen into the retroperitoneum, and completely blocking the abnormal blood flow around the esophagogastric fundus by esophageal transverse anastomosis were effective. It is suggested that prospective studies can be carried out to observe the near- and long-term effects of this procedure and to evaluate whether it can be used as a standard procedure for portal hypertension. It is well known that it is easy to cut the spleen but difficult to preserve it. Splenic preservation surgery is often associated with a high risk of postoperative hemorrhage. Therefore, as mentioned above, spleen preservation should be adapted to the time, place, and person, and several methods should be used when available to ensure the safety of the surgery. It is generally believed that preserving at least 20% to 30% of the splenic tissue can ensure the normal function of the remaining spleen. In the case of splenic injury, it is necessary to choose one or several methods such as adhesive coagulation hemostasis, suture repair, splenic artery ligation, partial splenectomy, splenectomy combined with autologous splenic tissue transplantation, etc. According to the site and degree of injury, there is also the use of radiofrequency to treat splenic trauma and partial splenectomy, which has a good effect of hemostasis, and it can be tried [11]. Efforts should be made to preserve the splenic vasculature during pancreatic body tail resection by carefully separating the splenic vessels from the pancreas and carefully ligating and severing the splenic arteriovenous branches. If there is any difficulty, the splenic artery should be cut off before the short gastric artery and the posterior gastric artery, and pancreatic caudal resection with preservation of the spleen and removal of the splenic vessels should be performed. During the operation, the pancreatic section should be handled properly, and the main pancreatic duct should be sutured, and it should be reconfirmed that there is no circulatory obstruction in the spleen before abdominal closure. Postoperatively, keep the drainage smooth and monitor the amylase level in the drainage fluid. When partial splenectomy autologous splenic tissue transplantation is performed in portal hypertension, care should be taken to preserve the splenic vascular branches or short gastric vessels, and the spleen should be transplanted in the retroperitoneal cavity above the left kidney where collateral circulation is abundant. Giant splenectomy is a difficult and high-risk operation, which can cause hemorrhage if not careful, and blind clamping to stop bleeding in panic can easily cause damage to the stomach, colon, or pancreatic tail, which can lead to serious consequences in some cases (e.g., patients with portal hypertension). Giant splenectomy should pay attention to the following issues: ① according to the size of the spleen using the appropriate incision, good anesthesia and adequate exposure; ② separation of the peri-splenic ligaments and adhesions should be close to the spleen, from shallow to deep, the first easy to difficult, step by step, to prevent damage to the spleen caused by hemorrhage; ③ to avoid the large bunch of ligature, if necessary, ligature to seek to be precise, to prevent postoperative bleeding; ④ spleen should be mastered to move the strength of the spleen, do not use violence, rotate the spleen in a moderate manner, the splenic fossa promptly filled with warm saline. The splenic fossa should be filled with warm saline gauze in a timely manner; ⑤ Change the surgical strategy in time according to the actual situation; ⑥ If there is no contraindication, make preparations for splenic blood transfusion; ⑦ Remind the anesthesiologist to pay attention to the hemodynamic changes of the patient before and after the splenic incision; ⑧ Appropriate application of new techniques and equipment, such as LigaSure vascular closure system, can simplify the operation and the result is accurate; ⑨ After splenectomy, elevate the blood pressure, and carefully check the trauma for blood seepage; ⑩ Splenic fossa is routinely placed with two adhesive tubes for drainage, and negative pressure suction or cannula drainage is added when necessary.