Smooth muscles are frequent components of endometriotic lesions

Deep infiltrating endometriosis (deeper than 5 mm under the peritoneum) oft en takes the form of a nodular lesion (or 'adenomyotic nodule') consisting of smooth muscles and fibrosis with active glands and scanty stroma, Thus, among endometriotic lesions, a certain distinction is drawn between musculo -glandular lesions and glandular lesions composed of endometrial-like epith elium surrounded by a cell-producing (cytogenous) stroma, The aim of this s tudy was to detect by immunohistochemistry, with a monoclonal antibody agai nst muscle-specific actin, the presence of smooth muscles in 54 endometriot ic lesions originating from four different pelvic locations (peritoneum, ov ary, rectovaginal septum and uterosacral ligaments) and to quantify the smo oth muscle content, Smooth muscles were frequent components of endometrioti c lesions in pelvic locations. In addition, smooth muscles were significant ly (P < 0.001) more abundant in endometriotic lesions than in their respect ive unaffected sites. This finding supports, at least partially, the occurr ence of a metaplastic phenomenon in the pathogenesis of endometriotic lesio ns. The definition of distinct endometriotic entities based on the differen ce in the tissue composition of the lesions (endometriotic nodules versus a denomyotic nodules) is inconsistent with the very frequent presence of smoo th muscle cells in endometriosis irrespective of its localization.