Histological Evaluation of Endometriotic Lesions. Panel A is a section through a chocolate lesion harvested from the uterine surface at three months. Panels B and C are sections through blue lesions obtained at six months of disease from the uterine fundus (B) and 12 months of disease in peritoneal fat (C). Panel D is a section through a red lesion obtained at 16 months of disease from the peritoneal wall. The presence of endometriotic tissue is histologically confirmed by the presence of endometrial glands (indicated with arrows) and stroma (highlighted with asterisks): the stroma surrounding glands of endometriotic lesions ranges from only a few cells (as in B) to several cells in depth (as in C).