Risk factors associated with the higher incidence of interstitial ectopic pregnancy include uterine anomalies, pervious ectopic pregnancy or salpingectomy, pelvic inflammatory disease, in vitro fertilization and ovulation induction. However, in our index case, none of the above risk factors were noted suggesting the role of natural causes as well.
Interstitial ectopic pregnancy is associated with a higher risk of shock and hemoperitoneum than other forms of ectopic pregnancy, as well as with a higher risk of maternal mortality due to delayed diagnosis and high vascularity of the myometrium.[2
] The presence of an eccentrically located gestation sac with incomplete or asymmetric myometrial tissue, < 5 mm in thickness, is a highly suggestive but nonspecific indicator of interstitial pregnancy.[1
] The presence of an echogenic line between the gestation sac and the endometrial cavity, also known as the interstitial line sign, is highly sensitive and specific for interstitial ectopic pregnancy.[3
] Few reports exist of the utility of 3D transvaginal or endovaginal ultrasound (TVS or EVUS) in the diagnosis of interstitial ectopic pregnancy.[4
] The 3D scans are very useful in obtaining the coronal scans of the fundal region of the uterus, giving a better overview of the cornual regions of the uterus. The characteristic features of an interstitial ectopic pregnancy (also seen in our case) include a GS located eccentrically outside the endometrial cavity of the uterus, in the region of the fundus with no or minimal identifiable myometrial tissue on its lateral aspect. This eccentric location and superior and lateral myometrial stripes are better and easily visualized on coronal scans generated through 3D TVS, an infrequent achievement with 2D scans.
Treatment options for interstitial ectopic pregnancy include local injection or systemic therapy with methotrexate, local injection of potassium chloride, conservative laparoscopic surgery and uterine artery embolism and in emergency situations, cornuectomy or hysterectomy.[5
] Evidence of a hemorrhagic ectopic pregnancy is an indication for laparotomy.
To conclude, the diagnosis of an interstitial ectopic pregnancy is usually difficult and delayed resulting in high morbidity and mortality. In the present case, the diagnosis of an interstitial ectopic pregnancy was suggested on the basis of 3D transvaginal ultrasonography prior to the development of any complication, resulting in early management with a favorable outcome. This case thus highlights the role of 3D ultrasonography in cases of irregular bleeding or suspected early pregnancy, to diagnose or rule out unusual sites of ectopic pregnancy for their early safe management.