Resection of a mediastinal mature teratoma diagnosed owing to sudden chest pain with elevated preoperative serum CA19-9.

Mediastinal teratomas are typically benign and asymptomatic, but they undergo sudden enlargement or rupture into neighboring organs in some patients owing to intratumoral hemorrhage, leading to serious complications. We report the case of a mediastinal mature teratoma that was discovered because of the sudden onset of chest pain accompanied by elevated preoperative serum CA19-9 levels. The patient was a 43-year-old man who experienced sudden chest pain and was brought to hospital in an ambulance. Chest radiography and computed tomography revealed a mediastinal tumor and a serum CA19-9 level that was elevated to 4377 U/ml. The tumor comprised soft tissue, fluid, and cystic components. The histological diagnosis was mature teratoma with peritumoral bleeding. Most epithelial components, including squamous epithelium and similar components in the bronchi, showed positive results for CA19-9 on immunohistological examination. The postoperative course was uneventful, and serum CA19-9 levels normalized.