Endometrium is the thin lining of the uterus. In women of childbearing age who are not pregnant, endometrium normally is shed each month as menstrual flow.
Endometriosis is a condition wherein there is presence of tissue that looks and acts like endometrium, but is located outside the uterus, usually in the abdominal cavity.
You are right is suspecting that endometriosis could be the reason for your intermittent abdomen pain.
A pelvic examination can sometimes suggest the presence of endometriosis. A normal uterus is quite mobile, but the scarring of endometriosis can make it tender and fixed in the pelvis.
To confirm endometriosis requires a diagnostic laparoscopy. This is a procedure wherein a telescope is passed through the umbilicus to gain access to the pelvis so that the presence of endometriosis and its stage assessed. Ultrasound scans are useful to help diagnose endometriosis cysts affecting the ovary, but they may not work for endometriosis of the abdominal cavity,
I would recommend that you get a second opinion from an Ob/Gy so that the cause of your illness can be ascertained,
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Dr. Gupta