Ultrasound diagnosis of interstitial pregnancy: findings and pitfalls.

The diagnosis of an unruptured interstitial gestation can be made by means of ultrasound examination. The most specific finding is an incomplete myometrial mantle around the sac. An eccentrically placed sac and failure to demonstrate the sac within the uterine cavity, i.e., near the internal os on the longitudinal scans, may be helpful ancillary findings. The differential diagnosis must take into consideration a pregnancy within one horn of a bicornuate uterus and a pregnancy within a myomatous uterus. Although this is a rare condition, it carries significant mortality if it ruptures. Diagnosis prior to rupture will reduce mortality and offer the possibility of preserving reproductive capabilities.