Ectopic Pregnancy

The most reassuring sign that an ectopic pregnancy is not present is the sonographic demonstration of a normal intrauterine pregnancy. The presence of an intrauterine pregnancy decreases the risk of a concurrent ectopic pregnancy to 1 in 30,000 for a low risk patient and 1 in 5,000 for a high risk patient (history of pelvic inflammatory disease (PID), previous ectopic, infertility, tubal surgery). Transvaginal ultrasound, with a reported accuracy of greater than 90%, should routinely be used in the evaluation for ectopic pregnancy.

A variety of uterine findings can be seen with ectopic pregnancies. The uterus may be empty or contain endometrial fluid collection (called pseudo-gestational sac seen in 10-20% of cases). This should not be confused with an intrauterine gestational sac.

The most common adnexal (tubal) finding in the presence of an ectopic pregnancy is a complex adnexal mass which represents hemorrhage. Other adnexal findings include a normal adnexa or a well formed adnexal "ring" with or without a yolk sac or embryo. Hemorrhage, either within a fallopian tube or peritoneal space, may be the only sonographic finding at the lowest HCG levels. The posterior uterine cul-de-sac (Pouch of Douglas) should be carefully investigated since complex peritoneal fluid may be the only finding in 15% of ectopic pregnancies.

An exophytic ovarian corpus luteum can mimic an ectopic pregnancy. However, the corpus luteum usually contains more echoes than an adnexal ring and is demonstrated as intra-ovarian by transvaginal imaging. The majority of ectopic pregnancies. are on the same side as the corpus luteum and we routinely try to identify the corpus luteum in our ectopic searches. Doppler ultrasound may help differentiate luteal flow from trophoblastic flow.

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Human Reproduction, Lectures: Clinical Radiology