Lung Localization of Endosalpingiosis: Challenges of Rare Manifestation of Müllerianosis.

Endosalpingiosis (ES) is a benign, nonneoplastic condition of the Müllerian system characterized by the ectopic implantation of fallopian tube-like ciliated columnar epithelium. Unlike endometriosis, ES lacks endometrial stroma and therefore does not produce the characteristic hemorrhagic episodes or extensive inflammatory responses associated with endometriosis. Although ES is primarily identified in the visceral pelvic peritoneum, extrapelvic manifestations are exceedingly rare, with pulmonary and pleural localization, accounting for ∼0.1% of reports. This report describes the clinical presentation of thoracic ES in a 40-year-old woman who presented with catamenial spontaneous primary pneumothorax. Despite a remote surgical history for ovarian endometriosis 10 years earlier, the patient had a prolonged period of clinical latency and no evidence of current pelvic recurrence. Videothoracoscopic surgery revealed a 5-mm apical pulmonary nodule and diffusely calcified pleural plaques. Histopathology and immunohistochemistry are remain gold-standard diagnostic methods for differentiating ES from thoracic endometriosis syndrome or malignancy. The diagnosis was confirmed by epithelial immunoreactivity for Müllerian transcription factors (PAX8 and WT1), keratin 7, and estrogen/progesterone receptors, together with the absence of cluster of differentiation 10 expression, which argued against endometrial stroma, and calretinin negativity, which argued against mesothelial origin. The pathophysiology of thoracic ES may resemble that of pulmonary endometriosis, involving transdiaphragmatic or vascular migration of Müllerian cells. For symptomatic presentations, surgical excision combined with long-term suppressive hormonal therapy is recommended to reduce epithelial proliferation. Given that the emerging literature suggests a possible link between ES and gynecological malignancies, rigorous long-term postoperative surveillance remains essential.