Posterior Mediastinal Müllerian Cyst (Hattori’s Cyst): A Case Report and Review of Pathogenesis and Diagnostic Features

Background: Posterior mediastinal Müllerian cysts are radiologically nonspecific lesions whose tubal-type epithelium raises unresolved questions about tissue origin. We describe a symptomatic case and review the published evidence. Case Presentation: A 44-year-old woman had recurrent right-sided chest pain for 4 years. Computed tomography showed an 18 × 26 × 32 mm paravertebral cyst at T5–T7 with an attenuation of 8 Hounsfield units. Magnetic resonance imaging excluded spinal involvement. Video-assisted thoracoscopic excision was followed by uncomplicated recovery. Ciliated epithelium with paired box protein 8 (PAX8), estrogen receptor, and progesterone receptor expression supported Müllerian differentiation. At 11 months, chest pain had resolved and usual activities had resumed. Literature Review: A narrative review with a structured search included 61 previously published patients in 45 publications. The combined sample, including the present case, comprised 62 patients, of whom 60 were women and 2 were men. Thirty-six patients (58.1%) were asymptomatic. Proposed origins include developmental persistence, coelomic metaplasia, and vascular or lymphatic dissemination. None has been demonstrated directly. Reported follow-up was heterogeneous and does not support a reliable estimate of recurrence. Conclusions: Imaging defines location and cystic structure but cannot establish Müllerian differentiation. Diagnosis requires concordant morphology and immunohistochemistry, irrespective of patient sex. Minimally invasive excision can provide diagnosis and symptom relief when symptoms or diagnostic uncertainty justify intervention.