4.7 Differential Diagnosis
4.7.1 Pancreatic Ductal Adenocarcinoma（PDAC）
Patients with CP may also present with an apparent mass on cross-sectional imaging.Mass forming pancreatitis（MFP）need to be differentiated from PDAC.MFP and PC has similar findings:the hypo enhanced mass（arrow head）in the head of the pancreas，（2）the dilatation of the main pancreatic duct，（3）common bile duct stenosis Biochemical analysis has shown cholestasis and clinical jaundice.
Epidemiological studies have shown that the risk of development of PDAC is increased in patients with chronic pancreatitis（Lowenfels et al.1993）.In the subset of patients suffering from CP with IMH，PDAC was found in the pancreatic head in 3.5-6.8%（Lowenfels et al.1993；Talamini et al.1999）.The follow findings which are suggestive of malignancy include（1）a focal low-density mass，（2）pancreatic duct dilation upstream from the mass，（3）atrophy of the pancreas upstream from the mass，（4）the lack of features of CP（especially calcification），（5）vascular compression or obstruction with the loss of the fat plane between blood vessels and the mass，and（6）metastatic disease（Fig.7.13a-c）.
However，some cases of CP and PDAC are impossible to differentiate without surgical excision and histology.
4.7.2 Pancreatic Intraductal Papillary Mucinous Neoplasm（IPMN）
IPMN is a mucin-producing tumor，arising from the epithelium of the main pancreatic duct or side branches.Histologically，IPMN represents a spectrum of diseases，ranging from benign over borderline to frankly malignant tumors.According to their location，they are classified as main duct，branch duct，and combined type.Main duct type IPMN may show diffuse or segmental dilatation of the main duct due to mucin，typically hyper intense on T2-WI.A branch duct type is a multilocular cystic lesion，most often in the uncinate process，with communication to the（nondilated）main duct.A combined type will involve the main duct as well as side branches and show massive duct dilatation.(https://www.daowen.com)
Patients with CP may also present with a dilatation of the main pancreatic duct.dilatation of the main pancreatic duct need to be differentiated from main duct type IPMN（Fig.7.14a，b）.The retention cysts of CP need to be differentiated from branch duct type IPMN（Fig.7.14c，d）
Fig.7.13 Malignant transformation of chronic pancreatitis on CT.CECT axial（a）image shows extensive intraductal calcification and atrophy of the pancreatic parenchyma suggest chronic pancreatitis.An ill-defined low-density mass（arrows）adjacent to the pancreatic body（arrow）is seen on axial（b）image.CECT axial（C）image shows Double-duct sign is clearly seen with multiple intraductal calcification（arrows）in the dilated pancreatic duct（arrowheads）
The follow findings which can help us to differentiate them include（Talamini et al.2006；Kalaitzakis et al.2009）（1）patients with IPMN have a different male:female ratio，are older on average，have a lower alcohol intake and smoke fewer cigarettes than both patients with CP.（2）Patients with IPMN，which remains unidentified after pancreaticojejunostomy（PJS），have a prolonged period of well-being（several years）which is followed by recurrence of pain symptoms（leading to the correct diagnosis and to reoperation）.（3）Great care should be taken when diagnosing CP in patients who do not present typical characteristics of the disease，namely age over 50，moderate alcohol intake，nonsmokers，women，because there may be concomitant IPMN in such cases which is amenable to appropriate treatment.（4）Most of the patients with IPMN and a previous diagnosis of CP present with endoscopic appearances at onset which are not pathognomonic for IPMN（normal papillary opening，absence of mucus）and ERCP findings indicative of IPMN are only found a posteriori.（5）The different clinical characteristics at onset compared to CP and the anatomopathological data suggest that，in most cases，the IPMN was the cause and not a consequence of the CP.
Fig.7.14 Chronic pancreatitis was misdiagnosed as Pancreatic Intraductal Papillary Mucinous Neoplasm.A 38-year-old male with history of chronic upper back pain.CECT axial（a）image shows atrophy of the pancreatic parenchyma and irregular dilatation of the main pancreatic.Histological section（b）demonstrates a pancreatic parenchyma with abundant fibrosis（H&E，20×）.A 52-year-old female with history of alcohol abuse.CECT axial（c）image shows a small round cystic lesion communicated with main duct.Histological section（d）demonstrates bands of thick reactive fibro connective tissue arranged irregularly，creating a cystic cavity（H&E，20×）