RESUMEN
Background: Differential diagnosis of an eccentrically located sac includes interstitial pregnancy, true cornual pregnancy and angular pregnancy which may all look similar on 2D (two dimensional) ultrasound. Interstitial pregnancy is associated with a higher maternal mortality and needs to be differentiated from true cornual pregnancy and angular pregnancy. This paper is an illustration of the role of 3D (three dimensional) ultrasound in differential diagnosis and management of the three entities.Methods: 2D and 3D ultrasound findings were analyzed in 10 cases of eccentrically located sac. The role of 3D ultrasound in differentiating the three entities had been evaluated.Results: The presence of an eccentrically located gestation sac with incomplete or asymmetric myometrial tissue less than 5 mm in thickness on 2D and the coronal sections obtained from 3D scans were used for diagnosis of interstitial pregnancy in three cases. 2 cases of angular pregnancy were diagnosed based on the finding of sac located in one of the lateral angles of the uterus with broad based connection to the endometrium. 2 cases of cornual pregnancy one intrauterine in a bicornuate uterus and the other in a rudimentary horn has been described. One heterotopic pregnancy and two other cases where a cornual fibroid mimics interstitial pregnancy is also illustrated.Conclusions: The role of 3D ultrasound in differentiating the three entities and the key findings in obtaining the precise diagnosis are emphasized. Routine usage of 3D ultrasound in all cases of eccentrically located gestational sac is recommended.