Adenocarcinoma arising from an enteric cyst of the posterior mediastinum.

Mediastinal enteric cysts are rare congenital thoracic cysts. The majority of mediastinal enteric cysts occur in infants, while they are rare in adults. Although most of these cysts are benign, surgical resection is sometimes performed, and malignant changes found in enteric cysts are rare. A 52-year-old man was incidentally discovered to have a posterior mediastinal mass and we excised the mass thoracoscopically. Histopathological findings showed an enteric cyst with adenocarcinoma. Comparing the pathological and magnetic resonance imaging (MRI) findings, MRI would help to detect malignant changes in such cysts. Although malignant changes found in mediastinal enteric cysts are extremely rare, clinicians should always keep in mind that those cysts have malignant potential and careful evaluation of MRI would be a clue for surgical indication.