Interstitial pregnancy: a potential for misdiagnosis of ectopic pregnancy with emergency department ultrasonography.

Interstitial pregnancy is a rare and dangerous form of ectopic pregnancy that can be mistaken for a normal intrauterine pregnancy on ultrasonography, leading to catastrophic results. Increasingly, emergency physicians are using ultrasonography to diagnose intrauterine pregnancy. Emergency physicians should be aware of the potential for mistaking an interstitial pregnancy for an intrauterine pregnancy. We present a case report of an interstitial pregnancy misdiagnosed as an intrauterine pregnancy and discuss ultrasonographic and physical examination findings to help differentiate interstitial pregnancy from an intrauterine pregnancy.