Posterior fornix effusion is an exudative fluid in the posterior fornix of the vagina caused by inflammation, etc. The location of the posterior fornix is a depression behind the connection between the vagina and the cervix, which is called the utero-rectal fossa depression, so posterior fornix effusion is also called utero-rectal fossa effusion, and also called pelvic floor effusion. There are various causes of posterior fornix effusion, both physiologic and pathologic. Physiological posterior fornix effusion mainly occurs during menstruation and ovulation, the amount of fluid is very small, usually no obvious symptoms, most can disappear on their own, and does not require treatment. Pathological posterior fornix effusion is mostly caused by inflammation, that is, by chronic pelvic inflammatory exudation. A few are also caused by ruptured ectopic pregnancy, ruptured corpus luteum, pelvic abscess, chocolate cyst, ovarian cancer, etc. It is caused by acute and chronic pelvic inflammatory disease, mostly accompanied by lower abdominal pain, lumbosacral pain, history of abortion or medical abortion, etc. The specific cause of effusion is that the plasma exudate caused by inflammation cannot be absorbed by the body and slowly accumulates in the body.