Unicornuate Uterus

Unicornuate uterus results from complete or near complete failure of development of one Müllerian duct, leaving a single, banana shaped uterine horn with one cervix and one fallopian tube. It makes up about 2.5 to 13 percent of Müllerian anomalies, and about 1 in 4,000 women.

There may be a rudimentary horn on the opposite side (in about 65 percent): non-communicating, with or without functioning endometrium (about 33 percent of those), communicating, or absent. The ipsilateral kidney is absent or ectopic in 40 percent of cases.

Functioning endometrium in a non-communicating horn leads to haematometra, pain, retrograde menstruation and endometriosis, and a pregnancy in a rudimentary horn is an ectopic pregnancy with a high risk of rupture at 12 to 20 weeks.

• Often asymptomatic; normal menstruation; discovered during infertility or pregnancy workup.
• Cyclical or progressive pelvic pain and dysmenorrhoea if a non-communicating horn contains functioning endometrium; a tender, lateral pelvic mass.
• Pregnancy outcomes: first trimester miscarriage 25 to 30 percent, preterm birth 15 to 20 percent, ectopic pregnancy (including in a rudimentary horn), malpresentation (breech about 15 percent), fetal growth restriction, and live birth rates about 40 to 60 percent. Cervical insufficiency is common.
• Rupture of a rudimentary horn pregnancy: acute abdomen with intraperitoneal haemorrhage and shock, often at 12 to 20 weeks.
• Associated renal anomalies and skeletal anomalies.

• Three dimensional pelvic ultrasound shows a single curved, narrow uterus with an off midline position; look for a rudimentary horn, which appears as a separate mass adjacent to the uterus with myometrial thickness and a possible endometrial lining.
• MRI is definitive for classification, rudimentary horn status (communicating or not, functional endometrium) and associated endometriosis.
• Renal ultrasound to identify renal agenesis.
• Laparoscopy with hysteroscopy for definitive diagnosis, which also allows treatment.
• Early ultrasound confirmation in pregnancy to distinguish an intrauterine pregnancy from a pregnancy in a rudimentary horn (the gestational sac separate from the uterus, surrounded by a thick myometrial layer, with a vascular pedicle connecting the horn to the uterus).

• Asymptomatic women with no rudimentary horn or a non-functioning horn: no surgery. Counselling about pregnancy risks and early antenatal surveillance.
• Rudimentary horn with functioning endometrium (communicating or not): laparoscopic excision of the horn, ideally before pregnancy, to relieve pain, prevent endometriosis, and eliminate the risk of rudimentary horn pregnancy.
• The ipsilateral fallopian tube is also removed (salpingectomy), and the ovary is preserved. Dissect the horn from the unicornuate uterus with careful division of its attachment with a bipolar device, and close the uterus with 2-0 polyglactin sutures.
• Rudimentary horn pregnancy: once diagnosed, excision of the horn laparoscopically or by laparotomy before rupture. In rupture: emergency laparotomy, resuscitation, blood transfusion and horn excision. Methotrexate is not reliable in advanced cases.
• Metroplasty is not effective in unicornuate uterus because there is no tissue to unify; it is not indicated.
• Antenatal care: early ultrasound, cervical length surveillance every 2 weeks from 14 to 24 weeks, cerclage if there is an insufficiency history, vaginal progesterone 200 mg nightly if the cervix is below 25 mm, and growth scans.
• Observe for preterm labour. Give antenatal corticosteroids (betamethasone 12 mg intramuscularly twice 24 hours apart) before 34 weeks if delivery is imminent.
• Delivery: elective caesarean section at 37 to 38 weeks is common for malpresentation or previous loss, although vaginal birth is possible with a cephalic presentation. Postpartum haemorrhage prophylaxis.
• Assisted reproduction is used for infertility; transfer to the unicornuate cavity is straightforward, and the transfer of a single embryo is advised.