Pitfalls of MRCP in the diagnosis of pancreaticobiliary maljunction

Magnetic resonance cholangiopancreatography (MRCP) is useful for examining the pancreatic duct system in patients with acute pancreatitis instead of using endoscopic retrograde cholangiopancreatography (ERCP), as ERCP-induced pancreatitis represents a serious problem. However, we present here a case of idiopathic acute pancreatitis in which MRCP suggested pancreaticobiliary maljunction, but ERCP indicated normal pancreaticobiliary union.

A 22-year-old male was urgently admitted complaining of upper abdominal and back pain. He had no history of alcohol or drug intake. Serum amylase levels were elevated to 880 U/mL (reference value: less than 158 U/mL). Abdominal ultrasound demonstrated only a slight swelling of the pancreas, but no abnormal findings for the bile duct or gallbladder. Symptoms and hyperamylasemia improved with supportive therapy. Coronal heavily T2-weighted single-shot rapid acquisition with relaxation enhancement MRCP indicated a markedly long common channel, and pancreaticobiliary maljunction without biliary dilatation was diagnosed. Under the diagnosis of idiopathic acute pancreatitis associated with pancreaticobiliary maljunction without biliary dilatation, prophylactic laparoscopic cholecystectomy was planned. However, ERCP demonstrated a narrow main pancreatic duct and a normal common bile duct without the formation of a common channel. In a supine position, after withdrawal of the scope, the narrow main pancreatic duct at the head of the pancreas overlapped the lower common bile duct, giving the appearance of a long common channel as indicated by MRCP.

In MRCP of cases with a narrow main pancreatic duct, there is a possibility for false-positive indications of pancreaticobiliary maljunction. MRCP with secretin stimulation or ERCP should be performed in such cases.