A Rare Case of Incidental Catamenial Pneumothorax With Endometriosis-Related Ascites and Pelvic Endometriosis.

Endometriosis is characterized by the ectopic implantation of a functional uterine lining outside of the uterus. Commonly, it occurs in the fallopian tubes, ovaries, uterosacral ligaments, and gastrointestinal tract. Less commonly, it may occur in the pericardium, pleura, and central nervous system. Thoracic endometriosis syndrome includes multiple presentations, most commonly catamenial pneumothorax. We present a case of a catamenial pneumothorax that was incidentally found on imaging after the patient presented with complaints of abdominal pain and weight loss.