Endometriosis is characterized mainly by the presence of ectopic endometrial glands outside the uterine cavity. It was first reported by Carl von Rokitansky in 1860 , who named the condition ‘adenomyoma’. The pathogenesis of endometriosis is ascribed to one (or more) of three mechanisms: the retrograde regurgitation of endometrium through the oviducts during menstruation, Müllerian metaplasia of coelomic epithelium, or lymphatic and venous dissemination of endometrial tissue to distant sites with implantation .
Extra-pelvic (that is, non-gynecologic) endometriosis has received special attention primarily because of the diversity of affected sites and its unusual symptomatology. Extra-pelvic endometriosis may occur in any of four anatomical regions: the lungs, bowel-omentum, urinary tract, and all other sites inclusive . Explanations for the spread of endometrial tissues to distant sites rest on hypotheses of venous or lymphatic circulation, or analogies to the metastatic spread of neoplasms . Therefore, the hypothesis is that endometriosis does not result solely from retrograde bleeding, but also from endometrial cells that are shed in the pelvic cavity and which have a tendency to implant and proliferate [14–16].
New insights into the etiology and pathogenesis of this disease serve as a background for new treatments for disease-associated pain and infertility. Possible causal and supportive factors include genetic susceptibility, environmental factors, the immune system, intrinsic endometrial abnormalities, and the secreted products of endometriotic lesions . Importantly, affected women are at higher risk than the general female population of developing ovarian cancer, and may also be at increased risk of breast and other cancers, as well as autoimmune and atopic disorders. However, there may soon be a new repertoire of approaches for treatment and perhaps cure of this enigmatic disorder in the near future.
Endometriosis of the lung is a clinically serious form of the disease, which requires careful differential diagnosis, as in the present case. Our patient complained of hemoptysis, a clinical symptom of thoracic endometriosis, as is hematothorax and pneumothorax. Menstruation-related hemoptysis is not obviously present in all patients, and accurate diagnosis of thoracic endometriosis is always difficult to make. Fortunately, our patient presented with catamenial hemoptysis. Due to our interest in this case, we also reviewed 74 cases of catamenial hemoptysis that have been reported since 1956  in which ectopic endometriosis was identified: 37 cases (59.6%) (please correct to 0.5) were in the right lung, 19 (30.6%) in the left, and 6 (9.7%) were bilateral. In 61 of 70 patients (87.1%) who underwent gynecological examinations, no evidence of pelvic endometriosis was found [1, 6–8, 18–21]. Additionally, 58 of 73 cases (80.6%) (please correct to 74 and additionally correct the percentage)showed a history of gynecological disorders. These observations support the embolization theory as the underlying cause of ectopic endometriosis in the respiratory tract.
While in our case there was no proven pelvic endometriosis or gynecological disease, our patient has previously undergone induced abortions, and there were two cases in the literature review in which induced abortion may have caused endometriosis in the respiratory system. The CT findings for pulmonary endometriosis may include well-defined opacities, nodular lesions, thin-wall cavities, or bullous formations, but most cases involving hemoptysis have transient radiologic densities in the affected part of the lung . In our patient, the CT images taken during her menstrual period showed a radiographic opacity at the distal end of the left superior lobe. Of note, there was also active bleeding in the distal bronchus of the superior segment of the left lingular lobe detected by bronchoscopy on the fourth day of the menstrual cycle, which further strengthened the clinical diagnosis in the view of the CT finding. Ultimately, histopathological confirmation of ectopic endometriosis was obtained after exploratory thoracotomy.
In general, the initially important diagnostic criterion for this disease is presentation of periodic hemoptysis that is synchronous with menstruation. Most previously reported cases were diagnosed based on the clinical history of the patient; a histological confirmation of ectopic endometriosis is not always done. Fortunately, in the patient reported here, ectopic endometrium was found in the pulmonary parenchyma, and infiltration of hemosiderin-laden macrophages was observed that were the result of repeated bleeding episodes.
Patients with lung endometriosis usually undergo either surgery or hormonal treatments. However, no large-scale randomized trial has been conducted and the optimal treatment regimen remains controversial. Recently, video-assisted thoracic surgery for catamenial hemoptysis was reported, which was found to be safer and less invasive than lobectomy [9, 14, 23]. When the bleeding site is confirmed by bronchoscopy and it is determined to be distributed within one lobe, the surgical approach is considered appropriate for the disease, especially when the patient desires a pregnancy in the future or if they are worried about possible complications related to hormonal treatments. In addition, the treatment of catamenial hemoptysis by endoscopic laser ablation has also been reported, and this treatment modality should be considered if the lesion can be clearly detected by bronchoscopy [11, 13].
In the current case, a lobectomy provided a favorable outcome for this benign lesion, and endometriosis was confirmed via postoperative histopathology. Because of the history of hemoptysis synchronous with the menstrual cycle, an immunohistochemistry test was performed to ensure the preoperative diagnosis. Although we performed a lobectomy rather than the more minimally invasive video-assisted thoracic surgery (because the patient could not afford it), endometriosis-associated events were not present during the postoperative 2-year follow-up. Lobectomy was appropriate for the treatment of lung endometriosis in the present case, and its success lends support for the efficacy and safety of lobectomy for this disorder.
Further studies and a more extensive literature search are required to determine the best course of treatment for patients presenting with this rare disease. Systems biological approaches with patients and morphology-based mathematical modeling could be valuable for studying aspects of pathophysiology and for comparing variants of therapeutic modalities in depth. For the majority of women with endometriosis, the disease imposes a substantial toll in terms of well-being, personal relationships, time away from work, and the need for surgery and expensive therapies . Furthermore, the increased risk of ovarian cancer and possible increased risks of autoimmune diseases and breast and skin cancers further support a need for multidisciplinary care and long-term follow-up of women with this disorder .
For women in whom lung endometriosis is suspected, a current history of catamenial hemoptysis, active bleeding observed by bronchoscopy, and evidence from CT scans justify the preliminary diagnosis. The endometriosis patient’s history, environmental exposures, family history, and physical examination are considered just as important for assessment and care. Surgical removal remains the accepted treatment for the disease, and is supported by the outcome of our case. Appropriately designed clinical trials are essential for determining which therapies are safe and effective.