The tumor is often located in the head of the pancreas and can be multiple, with a peak incidence of 60-70 y. WHO pathology is divided into intraductal papillary mucinous adenoma, junctional tumor and papillary mucinous adenocarcinoma (including carcinoma in situ and invasive carcinoma).IPMN is an important precursor of pancreatic cancer. It is often associated with malignant tumors outside the pancreas, up to 29%, such as malignant tumors of the stomach, colon, and liver. The papillary structures within it often secrete large amounts of mucus, often reaching the jugular abdomen and filling the pancreatic duct. The tumor is divided into three types 1. Main pancreatic duct type: the tumor mainly grows in the main pancreatic duct with dilation of pancreatic duct, and the duct diameter is more than 1cm. 2. Branch pancreatic duct type: the tumor mainly grows in the branch pancreatic duct with dilation of branch duct, and is often located in the head of pancreas. It is often in the shape of a cloverleaf, unlike mucinous cystadenoma which has a “sac within a sac” change. 3.Mixed type: The tumor grows in the main pancreatic duct and branch pancreatic ducts, with both dilated. The main pancreatic duct is diffusely or stage-dilated with duct diameter greater than 5 mm, accompanied by cystic foci in the pancreatic head. 2. Branching pancreatic duct type: one or more cystic lesions in the pancreatic parenchyma without dilatation of the main pancreatic duct. 3, Mixed type: One or more cystic lesions in the pancreatic parenchyma with dilatation of the main pancreatic duct. However, it is difficult to distinguish the branching pancreatic duct type from the mixed type from the image. CT manifestations: 1. Branching pancreatic duct type: It is usually located in the head of the pancreas, but can also be located in the body and tail of the pancreas. They appear as clusters of small sacs with lobulated margins and visible separation within them. It can also show as a single-compartment lesion. The tumor is often not visible on CT and MRI because of its flattened shape. It is often accompanied by dilatation of the main pancreatic duct, which is filled with mucus secreted by the cause tumor. Mucus may be seen protruding into the duodenal lumen. Multiple occurrences are uncommon, accounting for approximately 30% of cases. The bulging duodenal papilla and the significantly dilated main pancreatic duct are commonly seen in malignant cases. 2, Main pancreatic duct type: It often shows moderate and significant dilatation of the main pancreatic duct. Small papillary tumors can be seen in the dilated pancreatic duct, but they are often not recognized by the naked eye because the lesions are often small or the lesions are flat. As with the branching pancreatic duct type, mucus-containing duodenal papillae may also be seen protruding into the lumen. The main point of differentiation from other cystic tumors is whether it communicates with the main pancreatic duct, and if it does, the diagnosis is clear, and MRCP and ERCP are more advantageous in showing that the lesion communicates with the pancreatic duct. Multi-layer spiral CT with surface reconstruction and oblique reconstruction can significantly improve its display rate. Pancreatic pseudocysts can be communicating with the main pancreatic duct, and it is difficult to differentiate between the two. The presence of a wall nodule protruding into the main pancreatic duct or within a cystic lesion is highly suggestive of a lesion of IPMN rather than a pseudocyst and plasmacytic cystadenoma. The disease is often associated with pancreatitis and calcification can occur in both. Therefore, the differentiation of the main pancreatic ductal type from chronic pancreatitis is also a challenge. The main point of differentiation between invasive IPMT and pancreatic cancer is the presence of stricture of the main pancreatic duct in the latter. Malignant signs 1. Involvement of the main pancreatic duct: Involvement of the main pancreatic duct suggests malignancy, mainly referring to lesions of the main pancreatic duct type and mixed type. While small branch pancreatic duct type often suggests benign lesions. 2, significantly dilated main pancreatic duct: the literature reports that the maximum diameter of the main pancreatic duct 10 mm as the boundary, the specificity of the diagnosis of malignancy is 92% and the sensitivity is 78%. Some authors also reported (RG) that the sensitivity and specificity were 20% and 95% with 15 mm as the boundary; 33% and 86% with 10 mm as the boundary; and 73% and 81% with 6mm as the boundary. 3, diffuse and multi-site involvement: Choi reported that if the main pancreatic duct is involved by more than 50%, it suggests that the lesion is malignant or junctional. Another author reported that if the entire pancreatic duct is involved, or if the lesion involves multiple sites (pancreatic head/hooks, pancreatic body, and tail), the sensitivity of the diagnosis of malignancy is 56% and the specificity is 77%. 4. The presence of wall nodules or solid masses. Highly suggestive of malignancy. The presence of a nodule larger than 3 mm in the main pancreatic duct or the capsule is considered the presence of this sign. The specificity of the diagnosis of malignancy is 96% and the sensitivity is 67%. The thickened cystic wall and thickened separation also suggest malignant lesions. 5. Large lesions are suggestive of malignancy. The sensitivity and specificity of malignancy was 82% and 90% with 2 mm as the boundary, and the sensitivity of malignancy was 54% and specificity was 94% with 5 mm as the boundary of RG. Large lesions are suggestive of malignancy, but it should be noted that some small lesions can also be malignant. Another group of lesions: for the branching pancreatic duct type and the mixed type, the diameter of cystic lesions is larger for malignant lesions, with a mean of 43 mm and 28 mm for benign ones, with statistical differences between the two. Generally, 3.4 cm is often used as the threshold for determining benign and malignant. Wall nodules with a diameter greater than or equal to 3 mm were found in 13% of benign cases and 56% of malignant cases. Thickening of the cystic wall of a cystic lesion suggests a malignant lesion, which is not seen in 1 case in benign lesions. (Definition of cystic wall thickening: the maximum thickness of the cystic wall is greater than 3 mm and covers at least 1/3 of the cystic wall or dilated pancreatic duct). The presence of septa suggests a malignant lesion. 6. Presence of calcification. It is still controversial. 7, dilatation of the common bile duct suggests malignancy. the sensitivity of RG for the diagnosis of malignancy is 60% and the specificity is 95%. 8.Malignant cases may be accompanied by enlarged lymph nodes, but no one case was accompanied by distant metastasis, and no one case showed peritoneal metastasis. Differentiation between carcinoma in situ and invasive carcinoma 1. In general, a mass in the pancreas suggests invasive carcinoma, while a papillary nodule often suggests carcinoma in situ. Among the 25 cases of carcinoma in situ, 14 cases showed wall nodules. In contrast, among 21 cases of invasive carcinoma, only 1 case showed wall nodules. Among the 21 invasive carcinomas, 17 cases showed infiltrative masses in the pancreatic parenchyma; among the 25 cases of carcinoma in situ, only 2 cases were seen. 12 of the 46 cases of malignant lesions were not diagnosed because of the absence of wall nodules and pancreatic parenchymal masses, and only 3 of these cases were invasive carcinomas. Therefore, in IPMT, the presence of pancreatic parenchymal infiltrative masses is highly suggestive of invasive carcinoma. 2. The ductal diameter of the main pancreatic duct and the size of the cystic lesion in the branch pancreatic duct type were not statistically different between the two. In general, the main pancreatic duct type and the mixed type were often malignant or had a propensity for malignancy (57-92%) and required surgical treatment. In the branched pancreatic duct type, the tumor is often benign or junctional, and the tumor grows slowly, so if the tumor is less than 2 cm, it can be followed up and observed. Prognosis: The 5-year survival rate is 44.4% for tumors invading the pancreatic parenchyma and 100% for those not invading the pancreatic parenchyma.