Ultrasound Imaging of Interstitial Ectopic Pregnancy

Ultrasound is a valuable tool in diagnosing interstitial ectopic pregnancy, a rare but potentially life-threatening form of ectopic pregnancy. Interstitial ectopic pregnancy occurs when a fertilized egg implants in the interstitial portion of the fallopian tube, which is the segment of the tube that passes through the muscle of the uterus. This type of ectopic pregnancy can be difficult to diagnose and carries a higher risk of rupture and hemorrhage compared to other types of ectopic pregnancies.

When performing an ultrasound to evaluate for interstitial ectopic pregnancy, there are several key findings that should be assessed. These include:

1. Location of the gestational sac: In interstitial ectopic pregnancy, the gestational sac is typically located in the interstitial portion of the fallopian tube, which appears as a triangular or rounded structure seen within the myometrium (muscle layer) of the uterus. This location is outside of the uterine cavity but still within the muscular wall of the uterus.

2. Abnormal location of the gestational sac: One of the hallmark features of interstitial ectopic pregnancy is the presence of the gestational sac in a location that is separate from the endometrial cavity. This can be confirmed by visualizing the gestational sac outside of the uterine cavity and near the cornual region of the uterus, which is the area where the fallopian tube and the uterus meet.

3. Empty uterine cavity: Another characteristic finding in interstitial ectopic pregnancy is the absence of an intrauterine gestational sac or embryo. This can be confirmed by careful evaluation of the endometrial cavity for the presence of a normal intrauterine pregnancy, as well as by assessing the size and appearance of the uterus relative to the gestational sac.

4. Thin rim of myometrial tissue surrounding the gestational sac: In interstitial ectopic pregnancy, the gestational sac may be surrounded by a thin rim of myometrial tissue, which appears as a hyperechoic (bright) ring surrounding the sac. This finding is known as the interstitial line sign and is a reliable indicator of interstitial ectopic pregnancy.

5. Presence of a yolk sac or fetal pole: In some cases, the ultrasound may show the presence of a yolk sac or fetal pole within the gestational sac, confirming the presence of an embryo. However, in many cases of interstitial ectopic pregnancy, the gestational sac may be empty or contain only a gestational sac without a yolk sac or fetal pole.

In addition to these key findings, it is important to evaluate for signs of ruptured interstitial ectopic pregnancy, which can present with symptoms of abdominal pain, vaginal bleeding, and hemodynamic instability. Signs of rupture on ultrasound include the presence of free fluid within the abdominal or pelvic cavity, as well as evidence of active bleeding within the interstitial gestational sac.

In summary, ultrasound is a valuable tool in diagnosing interstitial ectopic pregnancy and can provide important information to guide management decisions. By carefully evaluating for key findings such as the location of the gestational sac, the presence of the interstitial line sign, and signs of rupture, ultrasound can help to accurately diagnose interstitial ectopic pregnancy and facilitate prompt treatment to prevent complications such as rupture and hemorrhage.