Ruptured interstitial pregnancy presenting as an intrauterine pregnancy by ultrasound.

Interstitial pregnancy is an uncommon subset of ectopic pregnancy in which the conceptum implants in the intrauterine portion of the fallopian tube. These pregnancies tend to progress further before rupture than do other tubal pregnancies and subsequently have greater propensity for massive intra-abdominal bleeding and maternal demise. Abdominal ultrasound can be deceptive in evaluating interstitial ectopic pregnancies. Transvaginal ultrasonography is more sensitive in the diagnosis of early ectopic pregnancy. Knowledge of the application and limitations of both transabdominal and transvaginal ultrasound will assist the emergency physician in the timely evaluation of this potentially lethal condition.