Recurrent rupture of a pancreatic mucinous cystic neoplasm with suspected main pancreatic duct communication, presenting with a mediastinal pancreatic pseudocyst, pancreatic pleural effusion, and pericardial effusion.

Spontaneous rupture of pancreatic mucinous cystic neoplasm (MCN) is rare, particularly outside pregnancy, and mediastinal extension has not been reported. We report a 34-year-old woman with a pancreatic tail MCN demonstrating continuity with the main pancreatic duct on computed tomography (CT), suggesting ductal communication. The neoplasm ruptured dorsally, and cyst fluid extended through the aortic hiatus, resulting in a mediastinal pancreatic pseudocyst, pancreatic pleural effusion, and pericardial effusion. Pleural fluid amylase was 1541 IU/L. Endoscopic ultrasonography showed a cyst-in-cyst architecture, and a preoperative diagnosis of MCN was made. After conservative treatment, the mediastinal lesion regressed; subsequently, symptoms recurred on day 5, and CT on day 7 showed a second rupture at a distinct site. Distal pancreatectomy with splenectomy was performed on day 58. Histologically, the lesion was an MCN with low-grade dysplasia, and the ovarian-type stroma was positive for estrogen and progesterone receptors. Epithelial denudation and ulceration extended well beyond the rupture sites, indicating diffuse inner-wall injury. These findings suggest that persistent inflow of pancreatic juice through the suspected communication may have contributed to recurrent rupture and mediastinal extension. Early surgical resection may be warranted when imaging suggests such communication. The patient has remained recurrence-free for 10 years postoperatively.