Cystic occupancy of the pancreas is a more specific type of pancreatic tumor, the incidence of which accounts for about l% of pancreatic tumors [1]. Because of the deep anatomical location of the lesion and long onset cycle, the clinical symptoms are not obvious, and early detection and diagnosis are difficult. With the development of imaging technology, the detection rate of cystic occupations of the pancreas has been increasing. Cystic occupations of the pancreas include primary cystic tumors and solid tumors with cystic changes. Clinically, they are generally classified into serous cystic neoplasm (SCN), mucinous cystic neoplasm (MCN) and intraductal papillary mucinous neoplasm (IPMN) In 2000, WHO defined the classification of pancreatic cystic neoplasm as SCN, MCN and IPMN, respectively, but a considerable part of the domestic literature is still accustomed to classify SPT as primary pancreatic cystic neoplasm [2]. For a long time, due to the low incidence and uncommon clinical cases of cystic tumors of the pancreas. There is a lack of awareness of its potentially malignant behavior, so that many inappropriate treatments occur in the clinic. Some patients miss the best time for surgery due to blind waiting and observation; another part of patients suffer from tumor recurrence or even metastasis due to incomplete resection caused by hasty surgery. Therefore, a correct understanding of the clinical characteristics of pancreatic cystic tumors is of great significance in guiding clinical treatment, selecting the appropriate treatment plan and timing, completely curing the tumor and reducing the recurrence and even metastasis of the tumor. 1. Classification of common primary cystic tumors of the pancreas 1.1. Clinical classification: The following three main pathological types are commonly seen in clinical practice: serous cystic neoplasm (SCN), mucinous cystic neoplasm (MCN), intraductal papillary cystic neoplasm of the pancreas ( intraductal papillary mucinous neoplasm (IPMN), IPMN). There are three types of tumors including benign, junctional and malignant tumors. Morphologic classification: There are usually four subtypes: microcystic, unicompartmental, multicompartmental, and with solid components. The microcystic type is only seen in plasmacytic microcystic adenoma, while the unicellular type can be seen in plasmacytic oligocystic adenoma, MCN, IPMN, etc. MCN is mostly located in the tail of the pancreatic body, with a round shape and smooth outline; IPMN mostly shows a pestle-like finger-like single capsule, and may be accompanied by pancreatic duct dilatation. Multi-compartmental type can be seen in plasmacytic oligo-cystic adenoma, MCN, IPMN and so on. When pancreatic cystic tumor with pancreatic duct dilatation, all three diseases are possible if pancreatic duct dilatation is only present at the proximal end of the tumor, while the whole or only distal pancreatic duct dilatation is only seen in IPMN, probably because the mucus secreted by IPMN tumor can obstruct the pancreatic duct anywhere and cause distal, proximal or whole pancreatic duct dilatation, while SCN and MCN are occupying effects causing pancreatic duct compression and dilatation, so they can only occur at the proximal end of the tumor. The tumor can only occur proximal to the tumor. Those with solid components include solid pseudopapillary tumors, cystic islet cell tumors, and cystic pancreatic cancer. The most common type is plasmacytic microcystic adenoma, which is characterized by multiple compartments (>6), small cysts (≤2 cm), and lobularity. Rare subtypes include plasmacytic oligocystic adenoma, solid plasmacytic adenoma, von Hippel-Lindau-associated cystic tumor, and plasmacytic cystic adenocarcinoma. It is also common in middle-aged and elderly women, with single- and multi-housed types, mostly in the tail of the pancreatic body. In multi-housed cases, the number of cysts is often C6, and the cystic cavity is large with a maximum diameter >2 cm and smooth margins; eggshell-like calcification of the cystic wall or partitions is seen in 10%-25%, and sometimes irregularities in the cystic wall, partitions and significantly enhanced solid parts are seen, all suggesting malignancy. It is more common in elderly men and includes main pancreatic duct type, branch pancreatic duct type and mixed type. The latter two types are often pestle-like in single-compartment cases and multicompartment cases often contain multiple forms of cysts, all communicating with the dilated main pancreatic duct. The cystic lumen communicating with the main pancreatic duct on imaging is a reliable sign for the diagnosis of IPMN. Solid pseudopapillary tumors occur mostly in young women with thicker envelope, intra-tumoral hemorrhage is seen, and progressive enhancement of the solid portion. Cystic pancreatic islet cell tumors are prone to calcification, and their vascular-rich features are seen on enhancement; even if the tumor reaches 95% of the cystic area, it can still show significantly stronger lesion margins in the arterial phase. Larger pancreatic cancers may occasionally undergo cystic necrosis with delayed enhancement of the solid portion, but the tumor grows infiltratively with indistinct borders and often invades adjacent tissues and blood vessels, often with dilated pancreatic ducts and bile ducts [3]. Pseudocysts are the most common secondary cystic lesions of the pancreas. Patients usually have a history of pancreatitis or abdominal trauma, and are often associated with increased blood and urine amylase. Imaging reveals a well-defined thin-walled or uniformly thick-walled cystic mass with secondary manifestations of pancreatitis, such as increased fat density around the pancreas and thickening of the left anterior fascia. The presence of debris within the capsule can be used to distinguish pseudocysts from cystic tumors. In general, the absence of enhancing soft tissue components within the pseudocyst is also a point of differentiation from cystic tumors. Pseudocysts <6 cm are usually self-resolving, and short-term follow-up to observe the progression of the disease can also help to differentiate them from cystic tumors. The history of the primary tumor or the discovery of metastases at other sites can help in the differential diagnosis. Cystic teratoma often occurs in children and young adults, and in addition to cystic components, fat and calcifications may also be found. Principles of management of cystic occupations of the pancreas Surgical resection is the main therapeutic measure for the radical treatment of cystic occupational lesions of the pancreas. Pre-surgical imaging combined with endoscopy are helpful in determining the plan and scope of surgery. Imaging examination helps to determine the location, size and relationship with surrounding organs and adhesions of cystic tumors of the pancreas. Ultrasound and CT can generally clarify the condition of the lesion. If the location of the tumor is deeper and CT etc. is not enough to give clear information, clear image localization can also be obtained by MRI. Endoscopy, ultrasound endoscopy and retrograde cholangiopancreatography can be used in judging the benign and malignant tumors, which can obtain effective histopathological information and help to further clarify the nature of the tumor. However, in most clinical cases, it is still difficult to determine the exact pathological type of pancreatic cystic tumor by laboratory and imaging examinations alone before surgery, and sometimes it is difficult to exclude the possibility of malignant tumor by histopathological biopsy, and for patients who are difficult to characterize, active surgery is an important means to prevent further malignancy of the tumor. Regarding the timing of surgery, some scholars believe that SCN is mostly benign. If the diameter of the tumor does not exceed 3 cm, and if the patient has no obvious symptoms and the tissue biopsy pathology excludes malignant tumor, we can choose not to operate temporarily and observe closely for follow-up. If the tumor increases rapidly during the follow-up period and the patient develops abdominal discomfort and other symptoms, then surgery should be actively performed. For patients who are unable to identify the pathological type of tumor, difficult to distinguish plasmacytic or mucinous cystadenoma, and patients with tumor diameter over 3 cm or obvious clinical symptoms, active surgery is recommended. Tumor resection should still be performed for those who cannot be clearly diagnosed plasmacytic cystadenoma or cause clinical symptoms. On this basis, it is proposed that an individualized surgical plan can be developed for the specific patient, and the specific timing and surgical approach can be chosen for the patient itself. Some scholars also believe that all cystic tumors of the pancreas should be treated surgically as early as possible once they are detected. Because all cystic tumors of the pancreas, except plasmacytoma, have the potential to become malignant, early detection and early surgical treatment is the principle. At present, with the development of medical technology and the advancement of pancreatic surgical instruments and techniques, the safety of pancreatic surgery has been greatly improved. In some large pancreatic surgery centers, the surgical mortality and complications of experienced pancreatic surgeons have been reduced to very low levels, and the resection rate and postoperative survival of benign pancreatic cystic tumors are far better than those of malignant pancreatic cystic tumors. Therefore, we believe that for pancreatic cystic tumors, a preliminary staging diagnosis should be made based on the clinical features of the lesion as well as imaging characteristics, and surgery should be considered if the lesion is considered to be SCN and >3 cm; complete surgical resection is required for MCN and IPMN, and intraoperative cryopathological examination is emphasized to ensure negative margins. The specific surgical approach should be considered based on the tumor size, location, pathological type, relationship with the main pancreatic duct, and the overall condition of the patient’s body. The general principles are complete resection of the tumor, preservation of the normal pancreatic tissue as much as possible, and protection of the internal and external secretion function of the pancreas. It is important to note that a comprehensive intraoperative exploration of the pancreas is required. It has been reported that more than 40% of pancreatic intraductal papillary mucinous adenomas may be a multicentric lesion or a lesion involving the entire pancreatic duct at an early stage. Therefore, we advocate that intraoperative ultrasound positioning should be implemented in all units that have the conditions to avoid missing some microscopic lesions and multiple lesions, and intraoperative ultrasound can help determine the relationship between the tumor and the main pancreatic duct. Mucinous cystadenoma of the pancreas is a recognized precancerous lesion, and early surgical resection is the key to achieve radical treatment and improve prognosis. Even for infiltrative tumors, the outcome after radical resection is significantly better than that of pancreatic ductal adenocarcinoma. Mucinous cystadenoma of the pancreas occurs more often in the tail of the pancreas, and as the age of the patient increases, the probability of evolving from adenoma to invasive carcinoma gradually increases, so radical resection of the tumor should be performed. Intraductal papillary mucinous adenoma of the pancreas may also be combined with malignant transformation. Therefore, if there is a high suspicion of pancreatic intraductal papillary mucinous adenoma or solid pseudopapillary adenoma, early surgical exploration should be performed and the extent of resection should be determined by intraoperative combination with cryopathology, which can greatly improve the patient’s prognosis. If the margins are positive, the resection must be expanded until the margins are negative, sometimes even total pancreatectomy is required, and expanded lymph node dissection is required for invasive IPMN. The survival rate after total pancreas resection for invasive intraductal papillary mucinous adenoma is also significantly better than that of pancreatic cancer in the same period. In contrast, solid pseudopapillary tumor is an occult pancreatic exocrine tumor with high resection rate, long survival and satisfactory surgical outcome. Cystic tumors of the head and neck of the pancreas can be treated by pancreaticoduodenectomy. For mucinous cystic adenoma and pancreatic solid pseudopapillary tumor located in the head and neck of the pancreas without obvious invasive manifestations, pancreaticoduodenectomy with preservation of the pylorus is feasible, and segmental pancreatectomy or pancreatic caudal resection with preservation of the spleen is feasible for plasma cystic tumor located in the tail of the body of the pancreas. For tumors located in the body of the pancreas, segmental pancreatectomy with distal jejunal Roux-en-Y internal drainage of the pancreatic stump is performed to prevent pancreatic leakage. For plasmacytoid cystadenoma, if the tumor is superficially located at the head of the pancreas and the hook, and the maximum diameter is less than 2.5 cm, if there is no clear contraindication to surgery, simple tumor removal can also be performed, but it should be performed with caution and attention should be paid to the possibility of pancreatic leakage after tumor removal. However, it should be performed with caution and the possibility of pancreatic leakage after tumor removal should be noted. It is recommended for patients whose tumors are located on the surface of the pancreas, at a certain distance from the main pancreatic duct and without the required margin distance. However, the incidence of postoperative pancreatic fistula is slightly higher, and proper drainage must be placed [4]. Distal pancreatic resection is possible for tumors in the tail of the pancreas, and the spleen can usually be removed at the same time. For mucinous tumors located in the tail of the pancreas without obvious invasive manifestations, distal pancreatic resection can also be performed by severing the splenic artery and preserving the spleen in order to avoid serious postoperative infections and to meet the requirements of radical tumor treatment. In recent years, we have adopted laparoscopic distal pancreatic resection with preservation of the spleen for pancreatic tail tumors, which is safe, effective and has quick recovery.