Abstract
Mullerian cysts are benign tumors that are very rare in the posterior mediastinum. It is necessary to distinguish Mullerian cysts from benign tumors or other types of cyst in the posterior mediastinum. A 42-year-old woman visited our hospital for a routine check-up, and a mediastinal mass was identified on chest computed tomography (CT). Contrast-enhanced chest magnetic resonance imaging (MRI) revealed a 4.0 × 2.6 × 2.8-cm mass, and a neurogenic tumor or esophageal cyst was suspected. Single-port thoracoscopic surgery was performed for cyst removal. Histopathological examination of the resected tissue revealed that the cyst wall was covered with a single layer of ciliated columnar epithelium. Immunohistochemical staining revealed positivity for paired box gene 8 (PAX8), Wilms tumor protein 1 (WT-1), estrogen receptor (ER), and progesterone receptor (PR). Therefore, a diagnosis of mediastinal Mullerian cyst was made. Mediastinal Mullerian cysts should be included in the differential diagnosis of posterior mediastinal cysts. Cystic lesions in the posterior mediastinum should be removed surgically and undergo immunohistochemical examination.