4.8　Diagnostic Strategy

Transabdominal ultrasound（TUS）is generally used as the first imaging method for patients with suspected CP.The sensitivity reported for TUS in chronic pancreatitis ranges from 49 to 96%（Rosch et al.2000）.This variation reflects the morpho-While the sensitivity of TUS is low for early lesions，it may detect more severe pancreatic changes as well as extrapancreatic alterations such as，for example，bile duct dilatation and fluid collections.

Abdominal computed tomography（CT）scanning has good sensitivity for diagnosing moderate-to-severe CP（Stabile Ianora et al.2013）.However，the early changes associated with CP are more difficult to identify on CT.Diagnostic criteria are similar as for TUS.Yet，compared with TUS，CT is less operator dependent，not compromised by intervening bowel gas，and identifies sensitively pancreatic calcifications.As a rule，sensitivity of CT for CP depends on the severity of the disease and ranges from＜60 to 95%（Rosch et al.2000）.Yet，it should be kept in mind that in patients with early stages of CP frequently have normal CT findings.

MRCP has been emphasized that its sensitivity（81-100%），specificity（94-98%），positive（86-93%）and negative（94-98%）predictive values，and diagnostic accuracy（94-97%）are as high as those of ERCP，which makes MRCP a promising alternative to diagnostic ERCP（Merkle and Baillie 2006；Lara et al.2001；Sai et al.2008）.MRCP is noninvasive，avoids ionizing radiation and contrast administration，and does not routinely require sedation.Moreover，it can provide useful information on the parenchymatous organs in this region in combination with conventional cross-sectional magnetic resonance sequences.Although it has advantages，MRCP also has certain drawbacks.Small duct changes and calcifications are not readily detected，and most importantly，it does not allow simultaneous therapeutic intervention.While ERCP offers a therapeutic option in the same session after the diagnosis is made（e.g.，papillotomy，removal of choledocholithiasis，stenting of a biliary stricture），MRCP just offers the diagnosis.Clips，stents，pneumobilia，hemobilia，and ascites might result in artifacts and impede interpretation of the MRCP image.Despite the new technological advances in MRI，its resolution has remained lower than that of ERCP（Keogan and Edelman 2001）.Maybe the innovative secretin-stimulated MRCP，which permits the detection of pancreatic flow dynamics and assessment of pancreatic exocrine function，will improve the sensitivity of MRCP in future（Mensel et al.2014a；Wathle et al.2014）.(https://www.daowen.com)

ERCP is considered to be the most accurate test for the diagnosis of CP，with sensitivities of 70-90%and specificities of 90-100%（Clark et al.2016；Gooshe et al.2015）.ERCP is widely considered the gold standard for the morphologic diagnosis and staging of CP.The most commonly used method for staging CP is the Cambridge classification（Milosavljevic et al.2010）.In mild or early disease，side-branch ectasia can be visualized.In more advanced disease，irregularity and dilatation of the main pancreatic duct，as well as strictures，calcifications and cysts may be seen.In ERCP，slight changes are often difficult to detect and variable to interpret.It has been reported that in 30%of patients with small duct disease who have had a normal or near-normal ERCP，an abnormal secretin stimulation test can be found（Gupta and Toskes 2005）.Overall，ERCP is useful for those patients in whom other methods failed or are unavailable，in patients with a clinical pattern of recurrent acute pancreatitis，or when a therapeutic intervention is being considered（Safari et al.2016；Md and Md 2016）.The role of ERCP in the evaluation of those patients suspected of having sphincter of Oddi dysfunction as a contributor to acute recurrent pancreatitis or CP continues to be evaluated（Vitale et al.2009）.However，it should be noted that ERCP is invasive and has a substantial risk of complications，in particular acute pancreatitis.In a recent multicenter survey，the overall complication rate was 4%and the procedure-related mortality rate was 0.4%（Bolan and Fink 2003）.

The diagnosis of CP at EUS is based on the finding of abnormalities in the pancreatic duct and parenchyma（Stevens 2013）.EUS accurately diagnoses CP in most patients with ERCP-or pancreatic-function-test-proven CP.However，they also suggest that 25%of those patients with a normal ERCP and 40%of those with normal pancreatic function tests have an abnormal EUS（Forsmark 2000）；at present it is unclear if these patients have CP or if EUS produces false-positive results.

The main indication for EUS-guided fineneedle aspiration（FNA）in the pancreas is to obtain samples from an intrapancreatic mass.EUS is able to detect and target abnormalities of the pancreas that cannot be seen by other imaging procedures.EUS-guided FNA allow the histological analysis of tissue from the pancreas（Sey et al.2016）.The Trucut needle is helpful for diagnosing benign parenchymal diseases of the pancreas，such as autoimmune pancreatitis（Sey et al.2016；Nayar et al.2016）.Of particular importance is the potential to avoid unnecessary surgery（Chang et al.1997）.