The endometrium, the tissue that normally lines the female uterus, undergoes changes with each menstrual cycle. At the end of each cycle and after the lining has thickened in preparation for hosting a fertilised ovum, it sloughs off, detaches, and is expelled through the cervix and vagina in the process of menstruation. In<unk> , some endometrial-like tissue is found in other parts of the body; most often the pelvis and abdomen, the central nervous system, the nasal passages, skin and thorax. At these other 'ectopic' sites, endometrium tissue still responds to hormones with normal cyclical changes - bleeding roughly every 28 days. Theories explaining distant ectopic<unk>  include: * Vasculogenesis: Up to 37% of the microvascular endothelium of ectopic endometrial tissue originates from endothelial progenitor cells, which result in de novo formation of microvessels by the process of vasculogenesis rather than the conventional process of angiogenesis. * Lymphatic spread: endometrial fragments travel through the<unk>  duct and hilar lymph nodes, reaching the chest cavity and causing pulmonary or pleural<unk> . * Coelomic metaplasia theory: the pleura and peritoneum share the same embryological origin, both derived from mesothelium. A pathological stimulus could be responsible for inducing precursor cells (mesothelial stem cells) of the pleura or peritoneum in order to differentiate into endometrial cells. * Vascular embolisation: endometrial fragments are taken into the venous system, travel through the right side of the heart, and are deposited in the pulmonary circulation. The endometrial tissue settles in the lung parenchyma or pleura. A review of autopsy data showed that patients with<unk>  have bilateral pulmonary lesions, which supports the vascular embolisation theory. The pleural and/or diaphragmatic lesions were always found on the left side, which supports the theory of coelomic metaplasia.
Thoracic endometriosis
Cervical thymic cyst
Inguinal lymphadenopathy
Cervical lymphadenopathy
Subphrenic abscess
Lung hernia
Paraproctitis
Diaphragmatic hernia