This is a cross section of a rectal nodule of endometriosis invading the wall of the colon. This is the type of bowel wall involvement that can be seen with obliteration of the cul de sac. The centimeter scale on the scalpel shows that this nodule is over 2 cm in thickness. The inside lining of the bowel is toward the top by the 2 cm line, the reddish discoloration which might be the only visible evidence seen by the surgeon is at the bottom by the 0 cm line.