Intraductal papillary mucinous tumor (IPMT), sometimes called intraductal papillary mucinous neoplasms (IPMN) in the literature, is a neoplastic disease that occurs in the pancreas. It is a relatively rare cystic tumor of the pancreas, with an incidence of about 1%-2% of pancreatic tumors. IPMT is a cystic tumor of the pancreas that has been recognized in recent years. Its clinicopathological features are completely different from those of pancreatic ductal cell carcinoma, and should be brought to the attention of clinicians. It includes a large group of tumors ranging from atypical hyperplasia to invasive pancreatic cancer, which are characterized by papillary protrusion of the pancreatic duct epithelium with massive mucin production and exudation through the duodenal jugular papilla, as well as stimulation of dilation of the main or branch pancreatic ducts, with longitudinal extension of the tumor along the pancreatic duct and possible malignancy. In addition, since IPMT has the potential risk of developing into invasive carcinoma, timely and accurate diagnosis of the disease is very important. The characteristics of the disease are summarized as follows: 1. Nomenclature Intraductal papillary mucinous tumor of the pancreas is a cystic tumor of the pancreas that has been recognized in recent years. There have been different names for this tumor, such as mucus-producing carcinoma, hypersecreting mucus carcinoma, intraductal papillary tumor, ductal hypersecreting mucus tumor, intraductal carcinoma, ductal mucus-producing tumor, ductal extended mucinous cystadenoma and cystic adenocarcinoma, mucinous ductal extension disease, pancreatic ductal extended mucus-producing tumor, and intraductal papillary mucinous tumor of the pancreas. A Publication of the Interna2 tional Pancreatic Cancer Study Group (IPCSG, 1994), WHO (1996), the Armed Forces Institute of thePathology (AF IP), and the International Society for the Study of Pancreatic Cancer (ISPC). thePathology,AF IP, 1997) and the Japanese Pancreatic Cancer Management Statute (2002, 5th ed.) all collectively refer to IPMT as having features of pancreatic ductal epithelial papillary proliferation, mucus hypersecretion or both, [4 Guo KJ, Ma G] and it has become a widely accepted concept internationally. Nowadays, intraductal papillary mucinous neoplasm of the pancreas is the term that is adopted today to avoid confusion with some other mucus-producing tumors of the pancreas such as mucinous cystic adenoma of the pancreas or cystic adenocarcinoma. In 1996, the WHO classification method clarified the histological classification of IPMT, which was histologically classified into benign (intraductal papillary mucinous neoplasm), junctional (intraductal papillary mucinous adenoma with moderate atypical hyperplasia) and malignant (intraductal papillary mucinous carcinoma). The current nomenclature of IPMT is designed to avoid confusion with other mucus-secreting tumors of the pancreas such as mucinous cystic tumor of the pancreas (MCT), which tends to disseminate within the pancreatic ducts and the dilated pancreatic ducts are covered by papillary tumor epithelium. According to the origin of the tumor, IPMT is usually divided into three types: (1) main pancreatic duct type: the main pancreatic duct is dilated and the tumor is mainly present in the main pancreatic duct; (2) branch pancreatic duct type: the branch pancreatic duct is dilated and the tumor is not present in the main pancreatic duct; and (3) mixed type: the tumor is present in both the main pancreatic duct and the branch pancreatic duct. The current study shows that IPMT and MCT have the following common features: (i) both tumors originate from the pancreatic duct epithelium; (ii) both produce large amounts of mucin; and (iii) both have the pathological feature of papillary protrusion. The clinical features of IPMT include: (i) massive mucus production and retention in the pancreatic ducts, (ii) enlargement of the opening of the papilla due to mucus flow, (iii) development and dissemination mainly in the main pancreatic duct, (iv) rare tendency to infiltrate, (v) high surgical resection rate and good prognosis. The basic pathological changes of IPMT are abnormal mucus-secreting epithelium in the pancreatic duct leading to massive mucus retention, pancreatic fluid stasis and dilation of the pancreatic duct, which may extend along the surface of the pancreatic duct to form flat lesions, or may be arranged to form micropapillary or macropapillary lesions protruding into the lumen of the pancreatic duct. Histologically, the proliferating epithelium is often more than twice the size of normal cells and transitions from non-papillary to papillary hyperplasia. These changes suggest that IPMT includes the evolution from non-papillary and papillary hyperplasia to adenocarcinoma via adenoma. In contrast, the majority of MCT histology has an ovarian-type stroma, which is often round in shape, has a common envelope, is usually without dilatation of the main pancreatic duct, and is completely surrounded by fibrous tissue, and is usually seen in middle-aged women and in the tail of the pancreatic body. However, a few IPMT and MCT still have difficulties in pathologic diagnosis. It is generally believed that IPMT has no specific clinical manifestations at the early stage, but may present with abdominal pain, low back pain, wasting, jaundice, diarrhea, etc. Kimura et al. summarized the data of 259 patients with IPMT in Japan, Europe, and the United States and found that 51.8% had epigastric pain, 13.0% had weakness and poor appetite, and 13.0% had wasting. Toshifumi et al. reported that 23 out of 43 patients with IPMT had clinical symptoms, including 12 cases of abdominal pain, 5 cases of low back pain, 2 cases each of weight loss, diabetes mellitus and amylase elevation, and up to 58.6% of patients had pancreatitis. This may be due to the accumulation of large amounts of mucus in the pancreatic duct, resulting in high pressure in the pancreatic duct, rupture of small alveoli, and activation of pancreatic enzymes due to the overflow of pancreatic juice, which caused recurrent episodes of pancreatitis. In addition, 41.4% of patients have diabetes mellitus. Therefore, patients with recurrent episodes of pancreatitis and combined diabetes mellitus should be alerted to prevent misdiagnosis and underdiagnosis. IPMT patients have a certain family genetic predisposition and are often associated with malignant tumors of other organs. 4. Imaging characteristics On CT imaging, it mainly appears as grape bunch-like or lobulated cystic lesions with obvious dilatation of the pancreatic ducts, which are connected to the pancreatic ducts, and usually the solid components of the lesions are not easily revealed, and they appear as nodular soft tissue shadows, which are formed by the fusion of smaller cystic lesions. The main difference between IPMN and other cystic tumors of the pancreas is that the cystic lesions of IPMN are connected to the dilated pancreatic duct. The main difference between IPMN and other cystic tumors of the pancreas is that the cystic lesions of IPMN are connected to the dilated pancreatic duct, while other cystic tumors of the pancreas are not connected to the pancreatic duct. (1) Preferred site: IPMT is mostly located in the pancreatic head at the hook, followed by other sites such as the neck, body, and/or tail of the pancreas. (2) Tumor size: The average diameter of cystic lesions of malignant IPMT is larger than that of benign IPMT, i.e., if the diameter of cystic lesions of IPMT is greater than 30 mm as measured by imaging, it is more likely to be malignant. On the contrary, it is more likely to be benign. (3) Main pancreatic duct diameter: the average diameter of main pancreatic duct of malignant IPMT is significantly larger than that of benign IPMT, i.e., if the diameter of main pancreatic duct of IPMT is larger than 6.5 mm, it is more likely to be malignant, and vice versa, it is more likely to be benign. (4) Tumor wall and cystic lumen: The average diameter of malignant IPMT nodules is larger than that of benign ones; similarly, the presence of irregular thick septa in cystic lesions of malignant IPMT is more common than that of benign ones. Branched IPMT, pathological findings are adenoma, T2WI axial scan clearly shows a multifoveal cystic tumor located in the pancreatic barb with separation, no wall nodules are seen [9] MRCP images clearly show 2 cystic tumors in the grape bunches of the barb and tail of the cyst communicating with the pancreatic duct IPMT main pancreatic duct imaging presentation A : Obvious MPD dilatation of A : Obvious MPD dilatation of malignant IPMT patient s; B : BenignIPMT patient s , MPD < 6 mm(arrows) The size of the hooked tumor on ERCP image is significantly smaller than that shown by MRCP, and the caudal tumor is not shown MRI can show the main pancreatic duct type T2WI shows a high signal dilated main pancreatic duct, with diffuse dilatation, segmental dilatation The main pancreatic duct can be seen as a high-signal dilated main pancreatic duct with diffuse dilatation and segmental dilatation. The branched type presents as a grape bunch or a single long T1-long T2 signal tumor with an average diameter of 6 cm (2 cm to 9 cm), some of which have wall nodules with an average diameter of about 2 cm (1 cm to 4 cm). The tumor is often associated with varying degrees of pancreatic atrophy and case calcification, or with dilatation of the main pancreatic duct. Enhanced MRI shows significant enhancement of the wall nodules. It also clearly shows the traffic between the branched type and the main pancreatic duct. ERCP shows enlarged large papilla with mucus flow, localized or diffuse main pancreatic duct dilatation and cystic dilatation of the branching pancreatic ducts, and filling defects due to the presence of wall nodules. In addition, ERCP can also be used to diagnose the fluid in the bursa and pancreatic ducts by aspiration under ultrasound guidance. In cases where it is difficult to differentiate from pancreatic cancer or chronic pancreatitis, ERCP can be the gold standard, and transoral pancreatic ductoscopy can reveal polyp-like masses in the main pancreatic duct or villi-like changes in the pancreatic duct mucosa. Intraductal ultrasound (IDUS) is complicated and not yet popular. However, data show that the detection rate of IDUS for nodular lesions, the detection of multiple lesions and the qualitative diagnosis rate are higher than that of ultrasound endoscopy (EUS). Although serum CA19-9 and CEA play an important role in the diagnosis of pancreatic ductal adenocarcinoma, serum CA19-9 and CEA levels are mildly to moderately elevated. The specificity of CEA is 91% and CA19-9 is 82%, but the sensitivity is unsatisfactory, 27% and 48%, respectively. Therefore, CA19-9 and CEA lack specific diagnostic value and cannot be used as an important basis for diagnosing IPMT or judging the benignity and malignancy. 6. Diagnosis of IPMT is very easy to be misdiagnosed: clinical symptoms lack obvious characteristics, and the degree of dilation of the duct and the amount of mucus produced determine its clinical symptoms and signs. (1) IPMT is not specific in terms of clinical symptoms and laboratory tests, so the diagnosis mainly relies on imaging and postoperative pathology. (2) The diagnosis of IPMT should be considered when the CT shows a lobulated or nodular cystic pancreatic mass with dilated pancreatic ducts. The clinical diagnosis can be made if ERCP examination is performed if an enlarged duodenal papilla, significant abnormal dilatation of the pancreatic duct and mucus overflow are found. Differential diagnosis Differentiation with mucocystic adenoma (carcinoma) is helpful for diagnosis. Similarities include: both tumors originate from the pancreatic duct epithelium, both produce large amounts of mucin, and papillary protrusion in the pancreatic duct is a common pathological feature. The differences are: IPMT occurs in men around 60 years of age, mostly in the head of the pancreas, characterized by dilatation of the pancreatic duct, and has a better prognosis. On the contrary, mucinous cystadenoma (carcinoma) is common in women around 40 years of age, and it is more common in the body and tail of the pancreas, usually large and round in shape, completely surrounded by fibrous tissue, not connected to the pancreatic duct, and has a poor prognosis. The clinical features of IPMT include: (1) large mucus production and retention in the pancreatic duct, (2) enlargement of the opening in the papilla due to mucus flow, (3) development and dissemination mainly in the main pancreatic duct, (4) little tendency to infiltrate, (5) high surgical resection rate and good prognosis. Through the above experience and pathological features, IPMT can be differentiated from other pancreatic tumors. The clinical manifestations of benign and malignant IPMT do not differ significantly. In general, it is believed that patients with malignant IPMT are relatively older and have shorter duration of symptoms; the possibility of malignancy is higher in patients with jaundice, because biliary obstruction is often caused by tumor infiltration of the bile duct wall. Sugiyama et al. reported that a main pancreatic duct diameter of ≥15 mm (main pancreatic duct type, mixed type) or a cyst diameter of >30 mm (branch pancreatic duct type) are all suggestive of a high possibility of malignancy, and therefore suggested that a main pancreatic duct diameter of 15 mm should be used as the threshold value for determining the benignity and malignancy of the lesion. In addition, IPMC accounted for 81.8% of cases in the main pancreatic duct type and 37.5% of cases in the branch pancreatic duct type, with a more obvious difference. Therefore, in China, Hu Xiangui [5] suggested that the possibility of malignant lesions should be highly suspected in cases with main pancreatic duct diameter >10 mm, tumor diameter >40 mm and main pancreatic duct type, and Kawai pointed out that when the tumor size exceeds 30 mm and the attached nodule exceeds 5 mm is an important basis for diagnosing IPMT as malignant. In China, Fan Fei [8] suggested that 30 mm can be used as a criterion to distinguish benign from malignant IPMT, that is, a tumor lesion with a diameter above 30 mm can be considered as malignant IPMT, if it is smaller than this value, the possibility of malignancy is small; similarly, for the diameter of the main pancreatic duct, the distinguishing value is 6.5 mm, and a diameter above 7.0 mm is more supportive of the diagnosis of malignancy. The presence of abdominal pain, jaundice or yellow urine, as well as a large tumor with a diameter of 30 mm or more, a raised nodule attached to the wall of the cyst, a significantly dilated main pancreatic duct with a diameter of more than 6.5 mm, and the presence of irregular thick septa in the cystic cavity of the lesion dividing it into one cystic cavity after another, can be used as many reliable indicators for the clinician to preoperatively determine the malignancy of IPMT, but they must be considered together. Only when multiple indicators meet the above conditions can we estimate whether it is benign or malignant. However, due to the special characteristics of IPMT tumors, the biological types of different parts of the same tumor lesion may not be the same, and the few tissues obtained by intraoperative frozen pathology cannot represent the pathological types of the whole tumor. Therefore, intraoperative fast-freezing pathology cannot be fully relied on. As IPMT and pancreatic ductal carcinoma have very different biological behaviors and prognosis, the principles of treatment are also different. However, it is still difficult to determine the preoperative benignity and malignancy of IPMT, and to determine the scope and extent of tumor invasion, so the choice of surgical method is still controversial. It is generally believed that the preoperative consideration of benign IPMT favors surgical options that preserve pancreatic and gastrointestinal functions, including pylorus-preserving pancreaticoduodenectomy (PPPD), duodenal-preserving pancreatic head resection, localized pancreatic hook resection, segmental pancreatic resection, and spleen-preserving pancreatic tail resection. If preoperative or intraoperative IPMT lesions are found to have a tendency to extend along the pancreatic duct, the extent of resection can be determined by intraoperative frozen section to ensure negative margins. For junctional IPMT or non-invasive malignant IPMT, partial pancreatectomy can be performed. Therefore, pancreaticoduodenectomy, total pancreatectomy or pancreatic tail resection and regional lymph node dissection are required for invasive carcinoma to reduce the recurrence of tumor after surgery. Since total pancreatectomy is very traumatic and seriously affects the postoperative quality of life, it is usually used only for patients with total pancreatic ductal lesions. If the risk of additional resection is estimated intraoperatively, partial resection is feasible if there is only heterogeneous hyperplasia at the severed end without infiltrating cancer. Duodenal papilloplasty can help mucus drainage and relieve symptoms, but only in cases that cannot tolerate pancreatectomy. Because of the significant differences in biological behavior and prognosis between IPMT and pancreatic ductal adenocarcinoma, the surgical treatment of IPMT needs to be further rationalized and improved. Intraoperative mucus leakage is one of the main causes of postoperative recurrence, and measures should be taken to avoid mucus dissemination and to flush the main pancreatic duct on the preserved side to remove the residual mucus in the pancreatic duct. The basic principles of the International Consensus Guidelines for the treatment of intraductal papillary mucinous tumors and mucinous cystic tumors (International Consensus Guidelines, 2005) are as follows: (1) Indications for surgery: main pancreatic duct lesions, pancreatic duct diameter > 1.0 cm; branch lesions, cystic mass diameter > 3.0 cm; cystic masses 1.0 to 3.0 cm in diameter, E Cystic masses of 1.0 to 3.0 cm in diameter, nodular lesions in the cystic wall, dilated main pancreatic duct, and positive cytological examination were found in EUS, MRCP or ERCP; recurrent pancreatitis due to mucus obstruction of the pancreatic duct. (2) Periodic observation: for cystic lesions with a diameter of 1.0-3.0 cm and no definite malignancy, periodic observation should be performed; CT or MRCP should be performed every 12 months for those with a diameter < 1.0 cm, every 6-12 months for those with a diameter > 1.0-2.0 cm, and every 3-6 months for those with a diameter 2.0-3.0 cm. The prognosis of IPMN is better, with a reported 5-year survival rate of 82.6% after IPMT, which is much higher than the 17.3% for common pancreatic ductal carcinoma. According to the national statistics of Japan in 2005, the 5-year survival rates of different lesions of IPMT were 100% for hyperplasia (54 cases), 99% for adenoma (436 cases), 100% for junctional tumor (9 cases), 98.4% for carcinoma in situ (159 cases), 88.9% for microinvasive carcinoma (84 cases), and 57.7% for invasive carcinoma (137 cases). The 5-year survival rate of benign lesions was 94%-100%, non-invasive carcinoma 77%-100%, and infiltrative carcinoma 24%-80%, according to the statistics of 11 English literature (879 cases) from 2000 to 2005. In addition, IPMT is often complicated by malignant tumors of other organs. The national statistics of Japan show that the complication rate of other malignant tumors in IPMT is 19% (79% of which are digestive tract cancers), which is much higher than that of pancreatic cancer (7%). In addition, about 11% of IPMT is complicated by pancreatic cancer. Therefore, systemic examination of the whole body should be performed during the follow-up observation of IPMT.