A hydrosalpinx is a condition that occurs when a fallopian tube is blocked and fills with serous or clear fluid near the ovary (distal to the uterus). The blocked tube may become substantially distended giving the tube a characteristic sausage-like or retort-like shape. The condition is often bilateral and the affected tubes may reach several centimeters in diameter. The blocked tubes cause infertility. A fallopian tube filled with blood is a hematosalpinx, and with pus a pyosalpinx.

Hydrosalpinx is a composite of the Greek words ὕδωρ (hydōr – "water") and σάλπιγξ (sálpinx – "trumpet"); its plural is hydrosalpinges.

Symptoms can vary. Some patients have lower often recurring abdominal pain or pelvic pain, while others may be asymptomatic. As tubal function is impeded, infertility is a common symptom. Women who are not trying to get pregnant and have no pain, may go undetected.

Endometriosis, ruptured appendicitis, and abdominal surgery sometimes are associated with the problem. As a reaction to injury, the body rushes inflammatory cells into the area, and inflammation and later healing result in loss of the fimbria and closure of the tube. These infections usually affect both fallopian tubes, and although a hydrosalpinx can be one-sided, the other tube on the opposite side is often abnormal. By the time it is detected, the tubal fluid usually is sterile, and does not contain an active infection. (Not symptoms)

The major cause for distal tubal occlusion is pelvic inflammatory disease, usually as a consequence of an ascending infection by chlamydia or gonorrhea. However, not all pelvic infections will cause distal tubal occlusion. Tubal tuberculosis is an uncommon cause of hydrosalpinx formation.

While the cilia of the inner lining (endosalpinx) of the fallopian tube beat towards the uterus, tubal fluid is normally discharged via the fimbriated end into the peritoneal cavity from where it is cleared. If the fimbriated end of the tube becomes agglutinated, the resulting obstruction does not allow the tubal fluid to pass; it accumulates and reverts its flow downstream, into the uterus, or production is curtailed by damage to the endosalpinx. This tube then is unable to participate in the reproductive process: sperm cannot pass, the egg is not picked up, and fertilization does not take place.

Other causes of distal tubal occlusion include adhesion formation from surgery, endometriosis, and cancer of the tube, ovary or other surrounding organs.

A hematosalpinx is most commonly associated with an ectopic pregnancy. A pyosalpinx is typically seen in a more acute stage of pelvic inflammatory disease and may be part of a tubo-ovarian abscess.