In a study of 44 patients with chronic pelvic pain, endometriosis was laparoscopically diagnosed in 36%, but histologic confirmation was obtained in only 18%. This approach resulted in a low diagnostic accuracy of laparoscopic inspection with a positive predictive value of only 45%, explained by a specificity of only 77% (247).
Microscopically, endometriotic implants consist of endometrial glands and stroma, with or without hemosiderin-laden macrophages (Fig. 17.6). It is suggested that using these stringent and unvalidated histologic criteria may result in significant underdiagnosis of endometriosis (5). Problems in obtaining biopsies (especially small vesicles) and variability in tissue processing (step or partial instead of serial sectioning) may contribute to false-negative results. Endometrioid stroma may be more characteristic of endometriosis than endometrioid glands (248). The presence of stromal endometriosis, which contains endometrial stroma with hemosiderin-laden macrophages or hemorrhage, was reported in women and in baboons and may represent a very early event in the pathogenesis of endometriosis (147,242,243). Isolated endometrial stromal cell nodules and immunohistochemically positive for vimentin and estrogen receptor can be found in the absence of endometrial glands along blood or lymphatic vessels (249).
Different types of lesions may have different degrees of proliferative or secretory glandular activity (248). Vascularization, mitotic activity, and the three-dimensional structure of endometriosis lesions are key factors (177,250,251). Deep endometriosis is described as a specific type of pelvic endometriosis characterized by proliferative strands of glands and stroma in dense fibrous and smooth muscle tissue (19). Smooth muscles are frequent components of endometriotic lesions on the peritoneum, ovary, rectovaginal septum, and uterosacral ligaments (252).
Microscopic endometriosis is defined as the presence of endometrial glands and stroma in macroscopically normal pelvic peritoneum. It is important in the histogenesis of endometriosis and its recurrence after treatment (253,254). The clinical relevance of microscopic endometriosis is controversial because it is not observed uniformly. Using undefined criteria for what constitutes normal peritoneum, peritoneal biopsy specimens of 1 to 3 cm were obtained during laparotomy from 20 patients with moderate to severe endometriosis (254). Examination of the biopsy results with low-power scanning electron microscopy revealed unsuspected microscopic endometriosis in 25% of cases not confirmed by light microscopy. Peritoneal endometriotic foci were demonstrated by light microscopy in areas that showed no obvious evidence of disease (255).
Figure 17.4 Laparoscopic excision of deep endometriosis from the cul-de-sac. (Photographs from Dr. Christel Meuleman, Leuven University Fertility Center, Leuven University Hospitals, Leuven, Belgium.) A: Extensive endometriosis with deep nodule at the right uterosacral ligament, masked by adhesions. B: Deep nodule still present in dense adhesion between rectum and uterosacral ligaments.
Figure 17.4 (continued) C: Cul-de-sac after resection of deep nodule with CO2 laser.