Pancreatic cysts can be divided into three types: true cysts (congenital cysts, retention cysts), cystic tumors (cystadenoma, cystadenocarcinoma), and pseudocysts. The most common type is pancreatic pseudocyst, which is a common complication of acute pancreatitis as well as pancreatic injury. As pancreatic fluid containing a variety of digestive enzymes exudes from the injured or necrotic pancreatic tissue into the retroperitoneal space around the pancreas, causing an inflammatory reaction and fibrin deposition, a fibrous envelope forms after a week to several weeks, and the retroperitoneum forms the anterior wall of the cyst. Alternatively, pancreatic fluid exudes directly into the small omental sac, the Winslow’s pore is closed due to inflammation, and the cyst forms within the small omentum. Sometimes pancreatic fluid enters other parts along the tissue interstices to form cysts in specific sites.The cyst wall of PPC is devoid of epithelial cells. I. Diagnosis and differentiation The diagnosis of PPC is not difficult, and the initial diagnosis can be made based on the medical history, symptoms and signs. The diagnosis can be further clarified with other examinations. 1. X-ray examination: Occasionally, calcified shadows are seen in the pancreatic area on plain films. Barium meal examination shows compression of the stomach and duodenum, with the stomach pushed forward and the duodenal arc widened. The transverse colon may have an insolid displacement. 2.B ultrasound examination: The sonogram is a typical transmissive dark area with generally irregular contours, smooth inner wall edges, occasionally lobulated, and sometimes scattered small dots of light are seen in the cyst. The echogenicity of the posterior wall of the cyst is enhanced. Huge cysts often show that the surrounding organs are pushed in different directions. The CT value is close to the density of water, between -6 and +14 Hu. PPC and pancreatic cystadenoma should be further differentiated on CT. Occasionally, pancreatic cancer can be identified as liquefied necrosis with a central low-density shadow to be distinguished from PPC, which has an irregular and thicker wall and an uneven density of the wall. 4.Amylase measurement: As the cyst fluid contains a large amount of amylase, which is absorbed through the cyst wall, the amylase in blood and urine can be increased, especially when the cyst is inflammatory, the blood and urine amylase is especially increased. 5.ERCP: It can determine the location of the cyst and help to differentiate it from pancreatic cancer. Pseudocyst ERCP shows cyst filling, main pancreatic duct obstruction, conical or truncated obstruction end, displacement of the common bile duct by compression, non-communicating cysts pancreatic duct branches by compression and limited branches not filling. However, about half of the pseudocysts do not communicate with the main pancreatic duct, so a normal pancreatic ductogram cannot negate the diagnosis, and ERCP can also check for the presence of fistula. However, ERCP can promote secondary infection or spread inflammation, so it should not be included as a routine test. 6.Selective arteriogram: It has a definite diagnostic value for pseudocysts and can show the lesion site. The cyst area appears as an avascular area, and the adjacent vessels are seen to be displaced and deformed. This test can correctly diagnose the vascular invasion, determine whether there is bleeding and the source of bleeding, and determine whether there is a pseudoaneurysm present in the cyst wall. Angiography is more valuable than ultrasound and CT in determining whether a pseudocyst has invaded the spleen. PPC needs to be differentiated from cystic tumors of the pancreas, hydronephrosis, mesenteric cysts, polycystic kidneys, and giant cysts of the left liver. PPC and PCT are not easy to distinguish clinically, the following points can help to distinguish: 1. PCT mostly has no history of pancreatitis and pancreatic injury, and is more common in older women, while PPC is mostly seen in young and middle-aged men, often with a history of pancreatitis and pancreatic injury. 2, PCT serum amylase is normal, while PPC often has elevated amylase in the acute phase. 3, ultrasound and CT examination: PCT is generally multicystic or separated, with a mixture of liquid and parenchymal parts, with a smooth and unevenly thick cyst wall, with central or peripheral calcification as its characteristics; not necessarily adherent to adjacent organs, with other parts of the pancreas normal. In contrast, PPC cysts have thick, opaque walls, are mostly single, without separation, and can adhere to adjacent organs. 4, PCT ERCP shows that the pancreatic duct is blocked or there is displacement of the pancreatic duct, and the cyst is not connected with the pancreatic duct, but PPC is mostly connected with the pancreatic duct in the acute stage. 5.PCT angiography shows that the cyst wall is richly vascularized or encapsulated, with tumor vessels or vascular envelope, while PPC has few vessels or the vessels are displaced by pressure. 6.Capsular wall biopsy should be considered as tumor if there is epithelial lining. 7.If the cyst persists without shrinking after sufficient decompression, it is suggested to be hard tumor wall and may be malignant. 8.Cyst fluid examination: B-ultrasound guided or intraoperative direct puncture to extract intracapsular fluid for determination of amylase, CEA, CA19-9 and cytological examination can help to differentiate PCT from PPC. Cystic tumor cystic fluid is clear and viscous, amylase is normal, while CEA or CA19-9 is obviously elevated, and exfoliative cytology examination has diagnostic significance; pseudocystic cystic fluid is gray or gutter water-like, with high amylase content. 9. Intraoperative exploration: cystic tumors are rarely adherent to adjacent organs, often multicystic, with uneven thickness of the cyst wall, the cyst wall may be calcified, and the cut surface is multi-roomed, but not connected to the pancreatic duct. The cyst contains fluid of different turbidity and viscosity. Pseudocysts are often closely adherent to the surrounding organs and are often unilocular, with uniform wall thickness and mostly turbid fluid. However, confirmation of the diagnosis still depends on intraoperative biopsy and postoperative pathological examination. It is best to perform preoperative puncture biopsy or intraoperative rapid frozen section examination, and intraoperative biopsy should especially emphasize multiple sampling in order to determine its nature. Second, clinical staging There are more ways to classify PPC, mainly centering on whether the pancreatic ducts traffic with the pancreatic cysts. About 1/3 of pancreatic ducts and cysts traffic by ERCP. freeny observed the relationship between pancreatic effusion and main pancreatic duct: 1. no traffic between cyst and main pancreatic duct; 2. traffic with proximal open pancreatic duct with distal pancreatic duct obstruction; 3. traffic with open pancreatic duct also without pancreatic duct obstruction; 4. traffic with distal and proximal pancreatic duct but proximal pancreatic duct obstruction due to stone or stenosis. D’Egidio (1991) classified PPC into 3 types: Type I: with acute pancreatitis, mature or immature cyst wall, and almost normal pancreatic ducts on ERCP. Type II: with acute attack of chronic pancreatitis, mature or immature cyst wall, common traffic with pancreatic duct, ERCP showed no obstruction of pancreatic duct, but signs of chronic pancreatitis (irregular twisting and bead-like changes in the main pancreatic duct and level 2 branches). Type III (retention): ERCP showed significant stenosis of the pancreatic duct. The cyst communicates with the pancreatic duct with chronic pancreatitis and the cyst is mature. The above two classification methods, each with its own characteristics, the latter classification method takes into account the changes in the course of the cyst and facilitates treatment. Treatment 1. Non-surgical treatment For patients in the acute stage of cyst formation within 6w, and cysts less than 6M, pharmacological treatment is feasible (mainly pancreatic secretion inhibiting drugs, such as Stannin, Sunnin, etc.), and dynamic observation of cyst changes, if the cyst is large, it can also be drained by percutaneous cyst puncture under the guidance of B-ultrasound or CT, which is simple, safe and effective, especially for pediatric injury PPC. It can be used as initial treatment, and the size and location of the cyst can be understood by drainage tube imaging, which provides the most direct basis for determining the surgical method. After evacuating the cyst contents, erythromycin or anhydrous alcohol can be injected into the cyst to promote the closure of the cyst wall adhesions. This method is suitable for early cysts with clear etiology and rapid enlargement with risk of rupture or causing gastrointestinal obstruction, especially for elderly people who cannot tolerate surgery. 2.Surgical treatment (1)Timing of surgery: the timing of surgery for PPC is crucial, it takes about 2w for PPC to form and 6w for cyst wall to mature. If the surgery is too early, the cyst wall is “immature” and has the possibility of self-receding, while if the surgery is too late, the complication rate of PPC increases. About 25%-70% of PPC with 4w-6w onset can dissipate on their own, while only about 5% dissipate on their own after 6w onset, and it is difficult to dissipate on their own for 12w or more, and 80% of patients will develop secondary diseases. Many factors affect whether the cyst can resolve and the speed of resolution, such as the size of the cyst, the thickness of the cyst wall, the presence of calcification, the presence of traffic between the cyst and the main pancreatic duct, and the degree of absorption of intracapsular fluid. It is generally believed that: cyst wall thickness; pancreatic duct and cyst traffic; chronic pancreatitis, the cyst exists for too long (>6 weeks), generally difficult to regress on its own. Hu et al. reported that the incidence of complications such as cyst rupture, bleeding and infection was nearly 40%, which is higher than the rate of natural dissipation of cysts. Some authors reported that the morbidity and mortality rate of those operated within 6w of cyst formation was as high as 60%, while the morbidity and mortality rate of late surgery was only 9%. Therefore, dynamic observation of cyst changes and selection of the most appropriate timing of surgery are the keys to reduce complications and decrease operative mortality. Determining whether the cyst wall has matured only based on clinical history and imaging examination may not be completely reliable, and the determination of serum old amylase (old amylase) can provide a reliable basis. The presence of old amylase is an isoenzyme produced by the removal of amylase from pancreatic amylase after it has been retained in the cystic lumen for a certain period of time, and the presence of this enzyme often indicates that the cystic wall has matured and internal drainage is feasible. If the enzyme continues to increase after surgery, it indicates recurrence of the cyst or the presence of a residual cyst. We believe that PPC generally requires surgical treatment unless the cyst is in the early stage of formation, the cyst wall is immature or the cyst is small. If the cysts are large or rapidly increasing with risk of rupture and cystic tumors of the pancreas cannot be excluded, surgery should be performed as early as possible. (2) Surgery: for patients in chronic stage, if the cysts are large or complications appear, surgery should be performed in a timely manner, and the surgery should be based on the time of cyst formation, disease stage, cyst size, location, number, the presence of complications and the patient’s general condition and other factors. ①External drainage: It is divided into cystostomy and cyst placement drainage. Cystostomy is a procedure in which the cyst wall incision is sutured to the abdominal wall so that the cyst contents can be drained directly to the outside of the body. This procedure is rarely used in patients with immature cyst wall but with infection, pancreatic abscess and poor general condition or pediatric injury PPC. this procedure can cause large amount of water, electrolytes, protein and pancreatic fluid loss, and has an erosive effect on local skin, and requires reoperation because of long-lasting fistula. Cyst placement drainage is only suitable for early cysts within 6w and cysts combined with infection, rupture or bleeding requiring emergency surgery, which can also result in loss of large amounts of pancreatic fluid, water and electrolytes, prone to the formation of pancreatic fistula and corrosive dermatitis. Some of them are prone to recurrence after external drainage, mostly due to poor drainage of cystic fluid and premature removal of drainage tubes. We advocate that after the cystic cavity disappears after multiple ultrasound, CT review or cystography before extraction, then try to clamp the tube for 1w, and then gradually withdraw the drainage tube, if the cystic cavity is not closed for a long time or accompanied by pancreatic fistula, the cystic cavity can be closed by injecting sclerosing agent or antibiotics through the drainage tube to promote adhesions. ② Internal drainage: It is currently considered the preferred surgical treatment method. It is suitable for those with high amylase content of cystic fluid, and is generally appropriate 6w to 12w after cyst formation. Anastomosis with stomach, duodenum and jejunum can be chosen, which is required to be physiological, simple and desirable, with unobstructed drainage, and can effectively avoid reflux. The most commonly used is the cystic jejunostomy Roux-Y anastomosis. The anastomosis should be placed in the lowest position of the cyst, and the caliber of the anastomosis should be greater than 5 cm. but postoperative recurrence of the cyst, bleeding or infection may occur. When performing internal drainage surgery, when the cyst wall is cut open to aspirate the cystic fluid, and check the thickness and smoothness of the cyst wall, if the thickness is uneven, attention should be paid to the presence of cystic adenoma or cystic adenocarcinoma, and the corresponding surgery should be performed after rapid frozen section. Pang Shuben et al. introduced the treatment of PPC with sequential external and internal drainage, which is characterized by a drainage tube lending itself to the gastric cavity and draining directly from the abdominal wall. The section of the catheter passing through the gastric cavity has no lateral holes, and the cyst only communicates with the outside world (external drainage). After a period of time the drainage tube is removed, if a pancreatic fistula exists, it flows directly into the gastric cavity and becomes internal drainage. This method requires the posterior wall of the stomach to be closely adhered to the cyst. The caliber of the drainage tube is P24 balloon catheter or myxoid catheter or other large caliber drainage tube. ③Cystectomy: theoretically, it is the most ideal and complete treatment method, especially for multiple cysts, which have the possibility of recurrence regardless of internal or external drainage. However, it is only applicable to those with small size of the tail of the pancreas and intact peritoneum. The practical application of large cysts is limited because of inflammation and close adhesion to surrounding tissues, and the cyst wall is surrounded by its adjacent intra-abdominal organs, which cannot be completely removed. If the possibility of pancreatic cystic tumor cannot be ruled out during surgery, part of the cyst wall tissue should be routinely excised for rapid frozen section examination to determine the nature of the lesion, and if it is a pancreatic cystic tumor, a partial resection of the cyst or the combined pancreas should be performed. (4) Pancreatic resection: commonly used for those who have serious lesions in the pancreas or cannot exclude cystic tumor of the pancreas, it is feasible to perform pancreatic body and tail resection, combined pancreatic tail and spleen resection, subtotal pancreatectomy or pancreatic head and duodenectomy. (3) Other drainage methods: ① Percutaneous aspiration and percutaneous drainage: under the guidance of CT or B-ultrasound, the fluid inside the cyst can be aspirated by puncturing the cyst, and the cyst can disappear in about 30% of patients. The disadvantage is that the fluid can be re-collected and repeated aspiration is required. During needle aspiration, a percutaneous drainage tube can be placed to eliminate repeated aspiration, especially for pseudocysts that communicate with the pancreatic duct. When there is no fluid flow from the drainage tube, it often means closure of the fistula and drainage can be stopped. However, care should be taken to remove obstruction of the drainage tube before removal. Percutaneous placement of drainage is indicated for both infected and non-infected pseudocysts with an efficiency of 67% to 91%. To prevent infection, the drainage tube should be repeatedly flushed. This method is simple, less traumatic and less complications, so it is worth to promote its application. However, it should not be used in cases where the cyst wall is thick, the cyst lumen is connected to the main pancreatic duct, the cyst has invaded larger blood vessels leading to hemorrhage or the cyst has broken into the abdominal cavity causing acute diffuse peritonitis. ②Endoscopic cystic intestinal anastomosis (ECE): there are two forms of ECE, one is endoscopic cystic gastric anastomosis (ECG) and the other is endoscopic cystic duodenal anastomosis (ECD); there are also a few endoscopically placed supported internal drains (Stent). The indications are that the stomach or duodenum is compressed by the cyst and the contact is very tight, i.e., there is a tight adhesion between the cyst and the stomach or duodenum or the wall of the cyst is not more than 1 cm away from the gastrointestinal cavity, and an “anastomosis” is formed by cutting open the stomach or duodenum and the wall of the cyst by electric knife or laser cautery under endoscopy. The use of transendoscopic placement of nasal cystic tubes and cystic gastric support internal drainage tubes has also been reported. A transduodenal papillary route has been advocated to place a catheter into the pseudocyst through the vater’s jugular. Yang Xiujiang et al. reported successful treatment of PPC by ultrasonic endoscopic puncture method of drainage. The experience of treating PPC with double “J” catheters and double pigtail catheters has also been reported.