AIM: To investigate the usefulness of secretin injection-MRCP for the diagnosis of mild chronic pancreatitis.

METHODS: Sixteen patients having mild chronic pancreatitis according to the Cambridge classification and 12 control subjects with no abnormal findings on the pancreatogram were examined for the diagnostic accuracy of secretin injection-MRCP regarding abnormal branch pancreatic ducts associated with mild chronic pancreatitis (Cambridge Classification), using endoscopic retrograde cholangiopancreatography (ERCP) for comparison.

RESULTS: The sensitivity and specificity for abnormal branch pancreatic ducts determined by two reviewers were respectively 55%-63% and 75%-83% in the head, 57%-64% and 82%-83% in the body, and 44%-44% and 72%-76% in the tail of the pancreas. The sensitivity and specificity for mild chronic pancreatitis were 56%-63% and 92%-92%, respectively. Interobserver agreement (κ statistics) concerning the diagnosis of an abnormal branch pancreatic duct and of mild chronic pancreatitis was good to excellent.

CONCLUSION: Secretin injection-MRCP might be useful for the diagnosis of mild chronic pancreatitis.

Chronic pancreatitis is morphologically characterized by irregular sclerosis associated with destruction and permanent loss of the exocrine parenchyma which may be either, focal, segmental or diffuse. These changes may present together with varying degrees of dilatation of the duct system at different segments[1]. Chronic pancreatitis is classified according to morphologic changes of the pancreatic ducts, as defined in the 1983 Cambridge Symposium[2].

MR cholangiopancreatography (MRCP) is a useful non-invasive technique to depict the projection images of the pancreatico-biliary tree, and is expected to become a valuable alternative to endoscopic retrograde cholangiopancreatography (ERCP)[3–8]. However, visualization of the branch pancreatic ducts by MRCP is not good[9–11], and there are few reports about the diagnostic value of MRCP in mild chronic pancreatitis (Cambridge classification). On the other hand, secretin injection-MRCP might allow better visualization of the pancreatic ductal system[12–16].

The purpose of this study was to evaluate the usefulness of secretin injection-MRCP for the diagnosis of abnormal branch pancreatic duct in patients with mild chronic pancreatitis.

Successful MRCP images were obtained after secretin injection in patients with mild chronic pancreatitis and control subjects. The rates for visualization of the main pancreatic duct on MRCP were 100%.

Abnormal branch ducts delineated on MRCP images correlated with ERCP images, lesion by lesion. The sensitivity and specificity for the diagnosis of abnormal branch pancreatic ducts determined by the two reviewers were 55%-63% and 75%-83% in the head, 57%-64% and 82%-83% in the body, and 44%-44% and 72%-76% in the tail of the pancreas, respectively (Table 1a and 1b). The sensitivity and specificity for the diagnosis of mild chronic pancreatitis (Cambridge classification) was 56%-63% and 92%-92%, respectively (Table 2). Interobserver agreement (κ statistics) for identifying abnormal branch pancreatic ducts and for diagnosing mild chronic pancreatitis was good to excellent (Table 3).

Early-stage chronic pancreatitis is difficult to diagnose because less obvious changes occur over time, before the development of overt exocrine or endocrine insufficiency and visible structural abnormalities[17]. Therefore, a major diagnostic challenge occurs when patients have clinical signs suggestive of chronic pancreatitis, in the absence of demonstrable pancreatic abnormalities on ultrasonography and CT. Reversely, in patients with advanced disease, findings such as atrophy, calcification, dilatation and stenosis of the pancreatic duct are obvious[18]. One of the earliest findings of chronic pancreatitis is an abnormal branch of the pancreatic duct detected by ERCP[218]. ERCP is the sensitive method for the diagnosis of early-stage chronic pancreatitis[19–21]; however, it is invasive and associated with complications[2223], because sufficient contrast medium must be injected to the peripheral branches of the pancreatic ducts when mild changes of chronic pancreatitis are sought[24].

Today, diagnostic ERP is challenged by MRCP, which is a noninvasive alternative to diagnostic ERP for the evaluation of normal and diseased pancreatic ducts[5–9]. However, it is difficult to delineate minimally dilated branch pancreatic ducts on MRCP despite its improved resolution because while on ERCP images the collapsed branches and main pancreatic duct are distended by the contrast medium, MRCP reflects the physiologic state of the pancreatic duct.

Since Takehara et al[10] first reported the MRCP images of moderate to severe chronic pancreatitis obtained after the injection of secretin; several authors have reported the usefulness of secretin injection-MRCP in the diagnosis of chronic pancreatitis[12–15]. Secretin stimulates fluid secretion in the ductal system; and increases the tonus of the sphincter of Oddi during the first 5 min, inhibiting the release of fluid through the papilla of Vater[9]. Therefore, secretin increases the absolute volume of intraductal free water and fills the collapsed branches with fluid[10], facilitating the detection of mild ductal changes in patients with mild chronic pancreatitis, even when no abnormalities can be demonstrated by MRCP under physiologic conditions. According to Mansfredi et al[25], visualization of the pancreatic duct branches improved from 71% to 100% in 93 patients with severe chronic pancreatitis and from 4% to 63% in 84 patients suspected of having pancreatic disease. Since the pancreatic juice secretion decreases in patients with advanced chronic pancreatitis, secretin injection-MRCP could be of diagnostic value for those with early-stage chronic pancreatitis, although the occurrence of mild chronic pancreatitis was underestimated by secretin injection-MRCP compared with ERCP in the present study.

There were some limitations to the present study. MRCP should be interpreted by someone blinded to the clinical information to avoid biases. Furthermore, although ERCP was chosen as the gold standard, it is well known that chronic pancreatitis may exist in the presence of a normal pancreatogram. Besides, parenchymal abnormalities may precede ductal and functional changes, and EUS is considered a more sensitive test for parenchymal abnormalities[26–30]. Therefore, the diagnostic value of secretin injection-MRCP for mild chronic pancreatitis might be limited.

In conclusion, secretin injection-MRCP might allow an earlier diagnosis of chronic pancreatitis and reduce the rate of false-negative cases detected with MRCP.