[1] Endometriosis is characterized by the presence of tissue similar to the lining of the uterus (the endometrium) forming abnormal growths elsewhere in the body.
Diagnosis is based on clinical history and examination, augmented with X-ray, CT scan, and magnetic resonance imaging of the chest.
[medical citation needed] 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 endometriosis, 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.
[medical citation needed] The diagnosis of thoracic endometriosis is primarily based on clinical history and examination, augmented with non-invasive studies such as X-ray, CT scan, and magnetic resonance imaging of the chest.
[citation needed] Definitive diagnosis is necessary to avoid unnecessary treatment and exclude more serious diagnoses (for example, haemoptysis, pleural effusion or cancer).