What is Pelvic Effusion Pelvic effusion is an accumulation of fluid in the pelvic cavity. The pelvic cavity refers to the area below the waist and within the pelvis, including the uterus, fallopian tubes, ovaries, rectum, bladder and other organs. Pelvic effusion occurs when fluid in the pelvic cavity is not absorbed. Pelvic effusion is not an independent disease, but a symptom that may be a manifestation of other diseases, so further examination and diagnosis and treatment are required. Pelvic effusion can be divided into many types according to the nature of the fluid, such as bloody, serous, purulent, inflammatory, etc.