**5.5 Lymphatic or vascular spread**

Evidence also supports the concept of endometriosis originating from aberrant lymphatic or vascular spread of endometrial tissue. Findings of endometriosis in unusual locations, such as the perineum or groin, bolster this theory. The lymphatic and hematogenous spread of endometrial cells can explain the presence of endometriosis in the pelvis or elsewhere. However, in the last few years, strong evidence indicates the possible role of immunologic factors and the lack of adequate immune surveillance in the pathogenesis of endometriosis (26, 27).
