RESUMEN
Endometriosis is a benign, inflammatory disease characterized by the presence of dysfunctional endometrial tissue outside the uterus. Typically confined to the pelvis, endometriosis is frequently associated with pain, dysmenorrhea, and infertility. Rarely, endometrial tissue has been documented to implant within the lung parenchyma and involve both parietal and visceral pleura of the thorax. Manifestations of thoracic endometriosis include catamenial pneumothorax, hemothorax, and hemoptysis. We present a case of thoracic endometriosis in a 43-year-old female who was found to have a loculated pleural effusion with an associated pleural nodule after gynecologic surgery. The patient underwent thoracotomy, decortication, and nodule excision. Pathology of the pleural nodule showed evidence of endometrial tissue within the parietal pleural. Thoracic endometriosis is a medical problem that is frequently undiagnosed and encountered by the practicing surgeon. Early diagnosis reduces both disease progression and late complications, allowing for early initiation of appropriate medical and surgical therapy.