D110-04 Surgically Resected Posterior Mediastinal Mullerian Cysts - Case Series of 3 Patients

Introduction With the increased use of radiographic imaging, incidental asymptomatic masses are being identified more frequently. Posterior mediastinal Müllerian cysts (Hattori’s cysts) can be one of these findings and are cysts arising from ectopic Müllerian tissue. Here, we present the first case series of three surgically resected posterior mediastinal Müllerian cysts (2017-2019) with a five-year follow-up. Case Series Three women were identified with asymptomatic posterior mediastinal masses on chest imaging. The patients included a 57-year-old postmenopausal woman (BMI 26), a 45-year-old premenopausal woman (BMI 43), and a 51-year-old perimenopausal woman (BMI 33). One patient was on hormone replacement therapy. Given the persistence of the masses and potential for growth, all three patients underwent surgical resection—one via video-assisted thoracoscopic surgery and two via robotic-assisted thoracoscopic resection—with intact cyst removal and uneventful recovery. All were discharged on postoperative day one. Five-year follow-up CT scans demonstrated no recurrence.Histopathology revealed cysts lined by ciliated cuboidal to columnar epithelium resembling fallopian tube mucosa. Immunohistochemistry was positive for estrogen receptor (ER), progesterone receptor (PR), PAX8, and WT1, confirming Müllerian differentiation and consistent with Hattori’s cysts. Discussion Just over forty publications have reported posterior mediastinal Müllerian cysts. Associations with obesity, hormone therapy, and prior gynecologic surgery have been common characteristics. Lesions are usually well-circumscribed, fluid-attenuated cysts on CT or MRI, and definitive diagnosis usually requires histopathology. Minimally invasive resection is both diagnostic and curative, with excellent outcomes and no known malignant potential.Our series supports prior findings of benign behavior and characteristic immunohistochemical profile. In those reported cases that are symptomatic, the most common include cough, chest pain, dysphagia, and dyspnea. Additionally, our findings corroborate the retrospective review by Sullivan et al., which reported a mean resected cyst size of 30.4 mm with a standard deviation of 11.5 mm. Definitive diagnosis of Mullerian cysts relies on histopathological confirmation. In addition to positivity for ER and PR, our specimens also demonstrated strong immunoreactivity for PAX8 and WT1, further supporting Mullerian differentiation. Conclusion From our literature review, this would be the largest reported series of resected Mullerian cysts with a five-year imaging follow-up showing no recurrence. Overall, Mullerian cysts are rare findings in the posterior mediastinum. However, in perimenopausal women aged 40-60 years, whether symptomatic or not, a cystic posterior mediastinal lesion should include Hattori’s cyst in the differential diagnosis. These cysts can be successfully resected using minimally invasive techniques, with excellent long-term outcomes.