Decidual cast mimicking an intrauterine gestational sac and fetal pole in a patient with ectopic pregnancy. A case report.

In a case of ectopic pregnancy, ultrasound findings showed a pseudogestational sac in the uterus containing debris that mimicked a fetal pole. Ultrasonography done one week before had revealed no intrauterine gestational sac. The progression in one week of an "empty" uterus to a seven-week-sized intrauterine gestational sac with the appearance of a fetal pole without a heartbeat should suggest to the sonographer the possibility of a pseudosac and ectopic pregnancy.