Endometriosis can actually occur in any organ of our body, although in the lower pelvis and the female reproductive organs are the most common locations.
Bowel endometriosis is not an uncommon as a location for endometriosis that is not confined to the female organs or the abdominal lining tissue (peritoneum) of the pelvis.
Bowel endometriosis origin is thought to be from the same medical issues that cause endometriosis in other parts of the body. But it is most likely that bowel endometriosis got there by being sperad through blood vessel channels or through lymph glands.
Since most of the lesions of endometriosis are quite small they can escape detection merely because of size. Intestinal endometriosis usually occurs on the 'outer' portion of the bowel wall, known as the serosa. Thus colonoscopy and barium studies of the bowel rarely identify endometriosis of the bowel because of this anatomic fact.
Pain with bowel endometriosis occurs from the same mechanisms of pain from endometriosis in other locations: some effect from the bleeding that occurs right where the implants are, pain from invasion of nerve cells by endometriosis, and pain from pain chemicals known as cytokines that are produced by the implants. Since the bowel is a large organ, the pain may be more intense than pain from endometriosis in other locations.
Diagnosis is thus best confirmed by laparoscopic surgeries, or by presumptive diagnosis based on symptoms. New treatments are on the way for endometriosis and thus new hope for those who suffer from this relatively debilitating form of pelvic problem.