The Second Report of Posterior Mediastinal Müllerian Cyst in a Male Patient.

Following the recent first report of a posterior mediastinal Müllerian cyst in a male patient (Mihara et al, 2026), we present the second documented male patient, confirming that this entity, previously considered exclusive to women since the 2005 description by Hattori, can indeed occur in men. A 51-year-old man was incidentally found to have a posterior mediastinal cyst during cardiac computed tomography. The 3.5 × 3 × 5.5 cm3 cyst at T4-T7 was resected via robotic-assisted thoracoscopy. Immunohistochemistry confirmed Müllerian differentiation (estrogen receptor+/progesterone receptor+/PAX8+/WT1+). This second male patient establishes that posterior mediastinal Müllerian cysts should be considered in the differential diagnosis of mediastinal cystic lesions regardless of patient sex.