Approximately 2% of all pregnancies are ectopic (i.e., implanted at a site other than within the uterine cavity). More than 95% of ectopic pregnancies are located in the fallopian tubes, with most in the isthmic or ampullary portion.

Women whose tubes are scarred or whose pregnancies were achieved by assisted reproductive techniques (e.g., in vitro fertilization) are at elevated risk of ectopic pregnancy. Because the incidence of pelvic inflammatory disease, which can result in tubal scarring, and the use of assisted reproductive techniques have increased over the past two to three decades, ectopic pregnancy has become more frequent than in the past.

Ectopic pregnancy typically presents clinically with pelvic pain and vaginal bleeding. Internal bleeding may occur and may, rarely, be severe enough to cause hypovolemic shock or death, especially if the diagnosis is delayed.

Ultrasound is the primary diagnostic modality for ectopic pregnancy. When a woman of childbearing age presents with pelvic pain or bleeding and has a positive pregnancy test (sometimes termed a “rule-out-ectopic” patient), ultrasound should be performed emergently and its interpretation should take into account the clinical presentation. In particular, the most likely cause of a complex adnexal mass in a “rule-out-ectopic” patient is ectopic pregnancy, whereas this diagnosis is highly unlikely in a woman with the same sonographic finding but a negative pregnancy test.

The sonographic finding that is definitive for ectopic pregnancy is visualization of a fluid-filled sac that lies outside the uterine cavity and contains either an embryo with cardiac activity (Figure 32.1.1) or a yolk sac (Figure 32.1.2). A more common, although less definitive, ultrasound finding in a woman with ectopic pregnancy is a complex extraovarian adnexal mass. In some cases, the mass is a fluid collection surrounded by a thick echogenic outer rim, termed a “tubal ring” (Figure 32.1.3), whereas in other cases, the mass has a solid or mixed solid and cystic appearance (Figure 32.1.4). There is sometimes a large amount of free intraperitoneal fluid and/or clotted blood in the pelvis (Figure 32.1.5).

The adnexal mass representing ectopic pregnancy often has high-volume, low-impedance blood flow around it when interrogated by color or spectral Doppler (Figure 32.1.6). Doppler, however, does not usually help substantially with the diagnosis of ectopic pregnancy because sonographic demonstration of an extraovarian mass and no intrauterine gestational sac in a “rule-out-ectopic” patient indicates a high likelihood (>90%) of ectopic pregnancy, regardless of the Doppler findings.

Interstitial (sometimes termed “cornual”) ectopic pregnancy is one that implants in the interstitial portion of the fallopian tube, the part of the tube that traverses the superolateral aspect of the uterus (the “cornu,” or “horn” of the uterus). This is an uncommon form of ectopic pregnancy but, like other ectopic pregnancies, occurs more frequently in pregnancies achieved via assisted reproductive techniques than those achieved naturally.

A gestational sac implanted in this location can grow for a period of time, but the myometrium around the interstitial portion of the fallopian tube has a far more limited ability to expand than does the body of the uterus. Continued growth of the gestational sac will lead to rupture and potentially life-threatening internal bleeding. Fortunately, pain usually occurs earlier than rupture, so prompt diagnosis when the patient presents with symptoms can save the patient’s life or spare her from a hysterectomy. Ultrasound-guided ablation is one of the treatment options.

On ultrasound, interstitial ectopic pregnancy appears as a gestational sac located in the superolateral portion of the uterus, bulging the external uterine contour, with little or no myometrium seen around the lateral or superior aspect of the gestational sac (Figures 32.2.1 and 32.2.2). A high volume of blood flow may be seen around the sac on color Doppler (Figure 32.2.2).