Discussion: A definite intrauterine pregnancy is present when a gestational sac with a sonolucent center (>5 mm in diameter) is surrounded by a thick, concentric, echogenic ring located within the endometrium and contains a fetal pole, yolk sac, or both.
A probable abnormal intrauterine pregnancy occurs when a gestational sac larger than 10 mm in diameter is present without a fetal pole or when a definite fetal pole is present without cardiac activity.
A definite ectopic pregnancy is characterized by the presence of a thick, brightly echogenic, ringlike structure outside the uterus, with a gestational sac containing an obvious fetal pole, yolk sac, or both.
Pregnancy of unknown location occurs with an empty uterus on endovaginal sonograms in patients with serum beta-HCG levels greater than the discriminatory cutoff value. In this case, an ectopic pregnancy is considered present until proven otherwise. An empty uterus may also represent a recent abortion.
Other ultrasonographic findings include an adnexal mass, free cul-de-sac fluid, and/or severe adnexal tenderness upon palpation with the probe. Patients with no definite intrauterine pregnancy and the aforementioned findings are thought to have a high risk for ectopic pregnancy.
An appreciation for the spectrum of ultrasonographic findings in ectopic pregnancy may enable radiologists to recognize an early ectopic pregnancy. Findings include the following:
- Tubal ring: Echogenic ringlike structure outside of the uterus representing early ectopic pregnancy.
- Extrauterine mass: Tender adnexal mass at US suggests an ectopic pregnancy. The findings of one study suggest that the presence of any adnexal mass other than a simple cyst is the most significant ultrasonographic finding in the diagnosis of ectopic pregnancy.
- Interstitial ectopic pregnancy: An interstitial ectopic pregnancy is one that implants at the highly vascular region of the uterus near the insertion of the fallopian tube. These types can grow larger than can those within the fallopian tube because the endometrial tissue is more expandable. Because of the increased size and partial endometrial implantation, these advanced ectopic pregnancies can be misdiagnosed as an intrauterine pregnancy. A clue to the diagnosis of an interstitial ectopic pregnancy is the eccentric location of the gestational sac. It is important to evaluate the amount of uterine myometrium surrounding the gestational sac and echogenic decidual layer. This thickness is called the myometrial mantle. At least 5 mm of myometrium should be present. A finding of less than 5 mm suggests the diagnosis. Another sonographic finding is the interstitial line sign.
- Heterotopic pregnancy: This is a combined intrauterine and ectopic pregnancy. It is thought to occur in approximately 1 in 3000 pregnancies and is more common in patients taking fertility agents.
- Extrauterine empty gestational sac: The presence of an extrauterine mass with a thick brightly echogenic band (rind) may represent an ectopic pregnancy.
- Hemosalpinx: The fallopian tubes may fill with blood or free fluid. One study found hematosalpinx as pathognomonic of ectopic pregnancy.
- Ruptured ectopic pregnancy: Findings on sonograms include free fluid or clotted blood in the cul-de-sac or intraperitoneal gutters, such as the Morison pouch.
