<prompt> Pain in endometrium is closely associated withsite of endometriumdepth of invasionstage of diseasesize of lesion  <response>: Ans B Ref: Williams gynaec page 230Underlying cause of pain is unclear: proinflammatory cytokines PGF2alpha released by the endometriotic implants into peritoneal fluidEvidence to suggest that pain from endometrium correlate to depth of invasion and site of pain- many indicate lesion location.Recent data suggest pain result from neuronal invasionRef: Sheila Balakrishnan, gynaec page 143Severe endometriosis can produce pain by peritoneal inflammation, deep infiltration and scarring, invasion of nerve endings, adhesions, collection of menstrual blood. 