A comparative study of ovarian and pelvic wall-infiltrating endometriosis

Study Objective. To compare the histology of ovarian endometriomas (OE) with that of pelvic wall-infiltrating endometriosis (PWIE) in an attempt to elucidate their histopathologic and clinical differences. Design. Retrospective histologic study. Setting. University-affiliated hospital. Subjects. Randomly selected tissue samples of 10 cases each of OE and PWIE. Interventions. Immunoperoxidase and Masson's trichrome stains were applied to the samples to determine the presence of myofibroblasts and collagen, respectively. Measurements and Main Results. All cases of OE showed changes suggestive of type 3 collagen deposition and myofibroblast proliferation. All cases of PWIE showed changes suggestive of type 1 collagen deposition and extensive smooth muscle metaplasia. The endometrial glands and stroma of OE tended to be on the inside lining of the chocolate cyst and did not freely intermix with native ovarian collagen. The lesions of PWIE, however, showed endometrial glands and stroma mixing freely with the native pelvic wall collagen. Conclusions. These findings suggest two different mechanisms for the pathogenesis of OE and PWIE and offer a rationale for using different surgical approaches to the different sites. Ovarian endometriosis is a lesion within the ovary with a response compatible with recent metastasis, whereas PWIE appears to be a metaplastic reaction.