Angular and interstitial pregnancies are ectopic pregnancies located around the entrance of the fallopian tube into the uterus in an area also known as the cornua of the uterus. Because they are surrounded by the muscular wall of the uterus, they both have similar presentations and are often used interchangeably. Cornual pregnancy although, is often used loosely to describe the above two, it is strictly speaking, an ectopic pregnancy located in the rudimentary horn of an abnormal uterus. Its frequency is however extremely very rare and its management is outside the scope of this discussion.
Anatomical differences however exist between the interstitial and angular pregnancies. While the latter is implanted into the part of the cornua lateral to the insertion of the round ligament of the uterus on the uterine fundus, the former is inserted medially to the origin of insertion of this ligament. Literarily, it means that while the former is found a bit closer to the tube, the latter is a bit closer to the interior part of the uterus. Even though both may present similarly and may rupture or tear the angle of the uterus as the fetus grows, resulting in massive bleeding, the latter has a higher chance of becoming fully intra-uterine, i.e. the fetus has a higher chance of sliding into the womb where it can continue to grow and thus a lower chance of rupture.
Interstitial pregnancies are found in about 4 % of all ectopic pregnancies and in about one in every 2,500 to 5,000 live birth. It is associated with about 7 times the risk of death compared to tubal pregnancies, largely as a result of massive bleeding. It is associated with a mortality rate of about 2.0 – 2.5%.
Although it shares some similar risk factors with tubal pregnancies, such as 1) a previous history of a ectopic pregnancy,2) pelvic infections 3) IVF and 4) IUD, the most important risk factor remains a previous history of an ipsilateral salpingectomy. A previous history of ipsilateral salpingectomy is present in about 37.5% of patients with interstitial/ angular pregnancy.
Because the pregnancy is located in the proximal part of the tube close to where the tube projects out of the womb, surrounded by some of the muscular wall of the uterus/womb, the ectopic pregnancy is better protected here than in any other part of the tube. Therefore, symptoms of the ectopic pregnancy may not manifest until about 3 months or 12 – 13 weeks of pregnancy due to distensibility of the surrounding myometrial wall, although rupture before 12 weeks of pregnancy are not uncommon. When they do rupture, the symptoms are similar but are often more acute than those of tubal ectopic pregnancies. They include abdominal pain, shock, dizziness and fainting attacks, all due largely to extensive bleeding from the rupture site into the abdomen. The growth of the fetus is however likely to occur way beyond the 12th week of pregnancy in angular pregnancies due to the increased surrounding uterine muscular wall compared to interstitial ectopic and many may be carried to term without any complications in some carefully selected cases.
This is similar to those done for tubal ectopic pregnanies. A definitive diagnosis may sometimes be reached with the aid of an ultrasound scan prior to rupture; otherwise, in most instances, a defintive diagnosis is usually made during surgery, only after the rupture of the ectopic pregnancy.
In clinically stable patients without any evidence of rupture, non-surgical management may be appropriate and include medical treatment with methotrexate alone or with UAE. Local injection of the ectopic pregnancy with methotrexate or potassium chloride under ultrasound or laparoscopic guidance can also be done.
Surgical intervention is indicated for cases with failed medical management, or based on patient’s preference after proper counselling or in cases where the patient is clinically unstable especially where findings suggest a ruptured interstitial pregnancy, such as patients presenting in pain or those with evidence of intra abdominal bleedig/hemoperitoneum on ultrasound scan. The surgical options include laparoscopy with cornuostomy or with salpingostomy or with cornual resection and salpingectomy with or without UAE.
Laparotomy and cornual resection is another option if the above is not available or in patients with clinically unstable heamodynamic features due to a ruptured interstitial ectopic pregnancy in which laparoscopy is not ideal. Hysterectomy is another option often reserved as a last resort in cases of severe intractable bleeding.
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