Endoscopic ultrasonography-guided drainage for spontaneous rupture of a pancreatic pseudocyst into the peritoneal cavity in a patient with autoimmune pancreatitis.

A 75-year-old man was referred to our hospital due to a huge pancreatic cyst. Computed tomography revealed a monocular cyst 15 cm in size without a solid mass lesion nearby. He was diagnosed with pancreatic pseudocyst. Endoscopic ultrasound (EUS)-guided drainage was planned for the next day due to abdominal distension; however, the pseudocyst ruptured into the peritoneal cavity before treatment could be applied. To prevent the progression of peritonitis, EUS-guided drainage of the pseudocyst was performed. A nasocystic tube and plastic stent were placed into the ruptured cyst via the gastric wall through the same puncture tract. After the treatment, the cyst rapidly decreased in size, and the peritonitis improved without surgery. The patient's serum IgG4 level was found to be elevated to 820 mg/dL. Endoscopic retrograde cholangiopancreatography revealed main pancreatic duct stricture without obstruction. No communication between the main pancreatic duct and the pseudocyst was found. An EUS-guided fine-needle aspiration biopsy of the hypoechoic site was performed, revealing IgG4-positive plasma cell infiltration. He was finally diagnosed with AIP associated with the rupture of a pseudocyst. Oral corticosteroid (30 mg/day) treatment was started and gradually tapered. There has been no recurrence in the 28 months since the initiation of treatment.