A cornual pregnancy is a rare type of ectopic pregnancy where a fertilized egg implants in the corner (cornu) of the uterus, near where the fallopian tube connects. It accounts for roughly 2 to 4% of all ectopic pregnancies and carries a mortality rate two to five times higher than other ectopic types, largely because it can go undetected longer and cause more severe bleeding when it ruptures.
Where Exactly It Implants
The uterus has two upper corners, each connecting to a fallopian tube. In a cornual pregnancy, the embryo implants in the muscular wall of one of these corners rather than in the main uterine cavity. This location is significant because the muscle there can stretch considerably before anything goes wrong, which delays symptoms and makes early detection harder.
You’ll often see the terms “cornual” and “interstitial” used interchangeably, and even medical textbooks disagree on the distinction. Some reserve “cornual” for pregnancies that occur in an abnormally shaped uterus (such as one with two horns), while others use it broadly for any pregnancy in that upper corner region. A related term, “angular pregnancy,” refers to implantation just inside the uterine cavity at its lateral angle, which sometimes has a better outcome. In clinical practice, the terms overlap enough that many doctors treat them as the same condition.
Why It’s More Dangerous Than Other Ectopics
Most tubal ectopic pregnancies cause symptoms within the first six to eight weeks because the thin fallopian tube can’t stretch much. The cornual region is different. It’s surrounded by a thicker layer of uterine muscle, so it can expand significantly before rupturing. Patients typically present between 7 and 16 weeks of gestation, well past the window when other ectopic pregnancies would have already been caught.
When the cornual wall does give way, the blood supply in that area is rich and direct. Hemorrhagic shock occurs in about 25% of patients with ruptured cornual pregnancies, which is a major reason the death rate for this type sits between 2% and 2.5%. If a cornual pregnancy continues past 12 weeks, the risk of uterine rupture climbs to roughly 20%. About 40% of hysterectomies related to ectopic pregnancy are performed because of ruptured cornual pregnancies.
Symptoms and How It’s Found
Early on, a cornual pregnancy feels no different from a normal ectopic or even a normal pregnancy. Many people experience no symptoms at all in the first several weeks. When symptoms do appear, they’re the same ones associated with other ectopic pregnancies: pelvic pain, vaginal bleeding, or both. If rupture has already occurred, the picture shifts to sudden, severe abdominal pain and signs of internal bleeding like dizziness, lightheadedness, or fainting.
Diagnosis relies on transvaginal ultrasound. Doctors look for a few specific signs: an empty main uterine cavity, a gestational sac positioned less than 1 centimeter from the outer edge of the uterus, and a thin rim of muscle surrounding the sac with increased blood flow. Even with these criteria, cornual pregnancies are notoriously difficult to identify on ultrasound, especially early on. Three-dimensional ultrasound can improve accuracy by giving a clearer view of where the sac sits relative to the uterine wall.
Treatment Options
Treatment depends on how far along the pregnancy is, how high the pregnancy hormone (beta-hCG) levels are, and whether rupture has already happened.
Medication
Methotrexate, a drug that stops the pregnancy tissue from growing, is the most common nonsurgical option. For ectopic pregnancies in general, it has a success rate around 91%, but for cornual pregnancies specifically, that rate drops to about 66.7%. The reason: cornual pregnancies are often diagnosed later, when hormone levels are higher and the pregnancy is more developed.
Methotrexate works best when beta-hCG levels are below 5,000 IU/mL and the gestational sac is smaller than 3 centimeters, with success rates reaching 88% under those conditions. It becomes significantly less effective when the gestational age passes 9 weeks, hormone levels exceed 10,000 mIU/mL, or a fetal heartbeat is visible on ultrasound.
Surgery
When medication isn’t appropriate or doesn’t work, surgery is the next step. The traditional approach involved open abdominal surgery with removal of the affected corner of the uterus (cornual resection) or, in severe cases, hysterectomy. Today, laparoscopic (minimally invasive) techniques have largely replaced open surgery for most patients.
Surgeons choose between two main procedures based on size. For smaller pregnancies under 3.5 centimeters, a cornuostomy (opening and emptying the cornual area while preserving uterine tissue) is often appropriate. For larger pregnancies over 4 centimeters, a wedge resection that removes a section of the uterine corner is typically recommended. In some cases, a cornuostomy is followed by a dose of methotrexate to ensure all pregnancy tissue is cleared.
Fertility and Future Pregnancies
Many people who have a cornual pregnancy go on to have successful pregnancies afterward, but those pregnancies carry elevated risk. Any surgery on the uterine corner leaves a scar, and that scar creates a potential weak point. Uterine rupture in a subsequent pregnancy occurs at a rate of less than 1% in women with a previously scarred uterus, with studies estimating roughly 0.65%, but the consequences of rupture are serious enough that close monitoring is essential.
A future pregnancy after cornual surgery is classified as high risk. Any abdominal pain during that pregnancy needs prompt evaluation with uterine rupture in mind. Delivery planning typically involves early discussions about whether a cesarean section is safer than vaginal birth, depending on how much uterine tissue was removed and how the scar healed.