Endometriosis lesions that compromise the rectum deeper than the inner muscularis layer have more than 40% of the circumference of the rectum affected by the disease.

Study Objective: To estimate the relationship between the depth of lesions of rectal endometriosis and the percentage of the circumference of the bowel segment affected by the disease.
Design: A prospective pathologic analysis of 45 surgical specimens of bowel endometriosis obtained by laparoscopic segmental resection of the rectosigmoid (Canadian Task Force classification II-1).
Setting: Tertiary referral hospital.
Patients: forty-five patients were submitted to a segmental resection of the rectum due to endometriosis between July 2004 and September 2006.
Interventions: Morphometric aspects of endometriotic lesions were analyzed, such as size and thickness of the lesion, deepest layer of bowel affected by lesion, and percentage of circumference of bowel affected by endometriosis.
Measurements and Main Results: Results showed that in lesions that reached the submucous layer of the bowel, the circumference affected was 31.6% greater than in lesions that reached only the outer muscular layer, whereas in lesions that reached the mucous layer, the circumference affected was 52.5% greater than in those that reached the outer muscular layer of the bowel. In addition, 89.3% of lesions with an affected circumference greater than 40% were those affecting the submucous or mucous layers of the bowel. These results suggest that when a lesion reaches these 2 deepest layers of the rectosigmoid, risk increases that the circumference affected will be greater than 40% (relative risk = 1.5; 95% CI: 1.0-2.3; p = .03).
Conclusion: In endometriotic lesions affecting the rectosigmoid beyond the inner muscular layer of the bowel wall, more than 40% of the circumference of the rectosigmoid is affected by the disease, confirming the recommendation of segmental resection of the bowel for this form of the disease.