Sonographic Characteristics and Key Diagnostic Signs of Interstitial Ectopic Pregnancy

Forty surgically proven cases of interstitial ectopic pregnancy (IEP) were reviewed for several signs and grayscale and color Doppler appearances, as well as for prospective interpretations by the interpreting radiologists. Prospectively, IEP was reported in 62.5%, with all reporting or describing a claw sign. The claw sign was identified on retrospective review in 100% of cases, thereby distinguishing the IEP from the more common tubal ectopic pregnancy (EP), which is separate from the uterus. The myometrial bar sign (myometrium between IEP and endometrium) was present in 100% of cases, allowing differentiation from an eccentric intrauterine pregnancy, which is peripherally located though completely surrounded by endometrium. The interstitial line sign was present in 22.5% of cases, considerably less frequent than prior studies, and was rarely used by the interpreting radiologists. The most common qualitative appearance of an IEP was a round mass (92.5%) with color Doppler flow (97.5%). An empty gestational sac (tubal ring) was present in 21 (52.5%), an embryo in 15 (37.5%), and a solid mass in 4 (10%). No cases of hematosalpinx were observed. Thus, the typical grayscale and color Doppler appearance of an IEP differs from the tubal EP, which most commonly presents as a mass without a visible gestational sac. In conclusion, IEP, a rare form of EP but with greater morbidity and mortality, is distinguished from a tubal EP and an eccentric intrauterine pregnancy by a combination of the claw and myometrial bar signs, use of which may potentially improve the diagnosis.