TABLE 1.

Summary of characteristics of extra‐pelvic endometriosis

	Symptoms	Laterality	Surgical treatment	Postoperative recurrence	Hormonal treatment	The most likely hypothesis on the pathogenesis
Abdominal wall endometriosis
Scar endometriosis	Swelling, pain, or bleeding at the lesion	N/A	Preferable	4.5%‐11.2%	OC, progestin, or GnRH agonist may be effective by long‐term use.	Endometrial cells are directly implanted via an iatrogenic process.
Umbilical endometriosis	Swelling, pain, or bleeding at the lesion	N/A	Preferable	Approximately 10%	Dienogest, GnRH agonist, or OC may be effective for relieving symptoms.	Spontaneous (endometrial cells migrate to the umbilicus through blood or lymphatic vessels) and iatrogenic (laparoscopic port site)
Inguinal endometriosis	Swelling, pain, or bleeding at the lesion	Predominantly in the right side	Preferable	0%‐16.6%	Dienogest may be effective for relieving symptoms.	Implantation theory (the peritoneal fluid containing endometrial cells enter into the inguinal ring, or endometriosis propagates from the pelvis to the groin via round ligament.)
Thoracic endometriosis
Catamenial pneumothorax	Dyspnea and chest pain	90% or more in the right side	VATS is a gold standard for diagnosis and treatment	14.3%‐46.7%	Long‐term administration is required.	Endometrial cells reach the right hemidiaphragm and migrate into the thoracic cavity through the defects of diaphragm.
Catamenial hemoptysis	Bloody sputum and chest pain	Equivalent	Mostly not required	Not reported	Effective	Lymphatic and hematogenous embolization of endometrial cells