The dilemma of eccentrically located gestational sac

The dilemma of eccentrically located gestational sac

1. The dilemma of eccentrically located gestational sac By Ahmed Moustafa Al- Amely Assistant lecturer of Obstetrics and Gynecology

2. Content Background Interstitial pregnancy Angular pregnancy Cornual pregnancy Take home message Reference

3. Background Early pregnancy scan is aimed at locating the sac and to check for fetal viability. The differential diagnosis of an eccentric located gestation sac includes interstitial, cornual and angular pregnancy. The lack of clarity in terminology used to define the several types of pregnancies that localize near the uterine cornua can have dramatic consequences. If the terms cornual, angular, and interstitial pregnancies are used interchangeably, there is substantial risk for intrauterine pregnancies to be inappropriately managed as ectopic pregnancies and vice versa. There remains significant opportunity to formulate and disseminate criteria that discriminate between and classify pregnancies that are only millimeters apart, but have disparate outcomes that range from the delivery of a healthy full-term infant to pregnancy loss and potential maternal morbidity. 

4. Interstitial pregnancy Although it is common to hear that ectopic pregnancies are those that are outside of the uterus, the increase in cervical ectopic pregnancies and cesarean scar pregnancies make evident that this description is imprecise.  An interstitial ectopic pregnancy implants in the interstitial part of the fallopian tube that passes through the cornual portion of the uterine myometrium. While these types of pregnancies could certainly still be considered within the uterus, like cervical and cesarean scar pregnancies, they lie outside of the endometrial cavity.  Interstitial tubal pregnancies are the least common of the tubal ectopic gestations and are estimated to account for 2–4% of ectopic pregnancies overall . They have a rupture rate of 13.6%, a maternal mortality rate of 2–2.5%, and have been quoted as accounting for 20% of all deaths attributed to ectopic pregnancy. 

5. Interstitial pregnancy One of the earliest published sonographic signs of an interstitial ectopic pregnancy is a very thin myometrial band measuring less than 5 mm around the border of the gestational sac and a separate empty cavity.  This sign is followed by another sonographic sign, the interstitial line sign ,which is an echogenic line that extends from the lateral corner of the endometrium and points to the ectopic pregnancy which represent the interstitial portion of the fallopian tube proximal to the ectopic gestation. However, a more important and useful finding is a band of hypoechoic myometrium along the inner border of the sac, between the endometrial cavity and the hyperechoic rim of the ectopic gestational sac. This band of myometrium causes a clearer separation of the sac from the endometrium. Another helpful finding is a color Doppler image showing a ring of the vessels around the ectopic gestational sac. 3D US is very helpful in differentiating an interstitial ectopic pregnancy from other types of cornual pregnancies

6. Interstitial pregnancy ( Ultrasound Criteria ) A n empty uterine cavity. A chorionic sac identified separately from the lateral edge of the endometrial cavity by at least 1 cm. A thin (5 mm) myometrial layer surrounding the chorionic sac . Presence of I nterstitial line sign. Absence of double sac sign. Ring of fire on color doppler US around the gestational sac.

7. Double sac sign Double sac sign is used to differentiate between intrauterine but eccentrically located pregnancies and interstitial ectopic pregnancies. It is used to verify all intrauterine pregnancies and uses the presence of two concentric sonolucent intrauterine rings surrounding the gestational sac to determine an early intrauterine pregnancy. These rings are thought to represent an outer normal peripheral decidual reaction and an inner chorionic ring.  .

8. Interstitial Pregnancy (1a) Transabdominal sagittal section of uterus depicting laterally placed sac. (1b) Transverse section at fundus of uterus illustrating eccentric sac. (1c) trans-vaginal image of sac seen separate from endometrial cavity. (1d) CRL measures 11 mm with cardiac activity. (1e) 3D image illustrating sac separate from endometrial cavity by an intervening myometrial band (arrows). (1f) 3D image showing thin myometrial mantle (arrows).

9. Interstitial Pregnancy Transvaginal transverse scan of the uterus (U) shows the eccentrically located interstitial ectopic pregnancy separate from the uterine cavity, containing a live embryo with a heartbeat. Note the thin mantle of myometrium surrounding the outer border of the gestational sac (arrows).

10. Interstitial Pregnancy Transvaginal transverse scan of the uterus (U) shows the eccentrically located interstitial ectopic pregnancy (arrows) separate from the uterine cavity. The open arrow points to the interstitial line sign, which extends from the endometrium toward the interstitial ectopic gestational sac (filled arrows).

11. Interstitial Pregnancy A , Transvaginal transverse scan of the uterus shows a left‐sided eccentrically located interstitial ectopic pregnancy separate from the endometrial cavity (E), which contains fluid. Note that the myometrium (long arrow) clearly separates the interstitial ectopic sac from the endometrial cavity and surrounds the sac (short arrows).  B , Transvaginal transverse scan of another uterus shows a right‐sided eccentrically located interstitial ectopic pregnancy (asterisk) separate from the endometrium (E). Note that a thin band of myometrium (long arrow) separates the interstitial ectopic sac from the endometrial cavity and surrounds the sac (short arrows).

12. Interstitial Pregnancy Three‐dimensional coronal image of a uterus with an interstitial ectopic pregnancy. Three‐dimensional coronal reconstruction from a transvaginal scan of the uterus shows an empty endometrial cavity (E) with an eccentrically placed gestational sac containing an embryo (asterisk) in the interstitial portion of the fallopian tube as it crosses through the cornual portion of the myometrium. Note a thin outer covering of myometrium (small arrows) and a thin band of inner myometrium (long arrow) separating the gestational sac from the endometrial cavity. By definition, this is an ectopic pregnancy ( ie , a pregnancy located outside the endometrial cavity).

13. Management of Interstitial Pregnancy Interstitial pregnancies can be treated with either non-surgical or surgical management. Nonsurgical treatment includes systemic/locally injected methotrexate and local injection of other cytotoxic drugs directly into the gestational sac. As first line of treatment, RCOG recommends methotrexate in patients with β- hCG < 5000 IU/mL and ectopic pregnancy smaller than 3.5 cm to 4 cm with minimal symptoms. Approximately 10% to 20% of patients with interstitial pregnancies who are treated with methotrexate will ultimately require surgery for a rising HCG level, continued pain, or evidence of cornual rupture. There have been only small case series of interstitial pregnancies treated with locally injected methotrexate or potassium chloride and a universally accepted protocol of either systemic single or multidose regimen or local injection has yet to be identified. Currently, there is no consensus as to whether cornuctomy , cornuostomy or hysterectomy is better, but however more conservative approaches are preferred like cornuostomy and laparoscopy instead of laparotomy for fertility conservation. Patients who are submitted to any of these treatments should ideally undergo caesarean section because of the risk of uterine rupture

14. Angular Pregnancy Most radiologists and many clinicians are not familiar with the term angular pregnancy. This condition refers to an implantation in the superolateral angle or corner of the endometrial cavity and results in the appearance of an eccentric gestational sac, which has been falsely called an ectopic pregnancy. In contradistinction to an interstitial ectopic pregnancy, an angular pregnancy implantation occurs in the superolateral angle of the endometrial cavity, medial to the uterotubal junction and medial to the round ligament, which can be seen on MRI. There is an adequate myometrial mantle surrounding the sac peripherally, and there is no intervening myometrium between the endometrial cavity and the gestational sac, as in an interstitial ectopic pregnancy

15. Angular Pregnancy T he terms angular and interstitial were being used synonymously for two very different types of laterally displaced or eccentric pregnancies. In an attempt to clarify the differences between these two types of gestations, they employed the use of laparoscopy to describe these pregnancies in relationship to the round ligament stating “The lateral uterine enlargement of an angular pregnancy displaces the round ligament reflection upward and outward. The swelling of an interstitial tubal pregnancy is lateral to the round ligament.”

16. Angular Pregnancy Angular pregnancy on ultrasound presents as an eccentrically located gestation sac implanted in the lateral angle of the uterus in the endometrial cavity. Most often there is sufficient myometrium surrounding the sac although focal thinning of myometrium may be seen sometimes. The “surrounding endometrium” sign has been recently proposed as a specific sign for angular pregnancies. This sign is based on the “double sac sign” (a layer of decidual reaction and a chorionic ring) seen in any intrauterine pregnancy should also be seen in an angular pregnancy but is not seen in interstitial pregnancy.

17. Angular Pregnancy ( Ultrasound Criteria ) Implantation of the embryo in the lateral angle of the uterine, cavity, just medial to the uterotubal junction. About 1 cm of myometrial thickness surrounding the gestational sac .  Presence of completely circumferential endometrium surrounding the gestation, and therefore diagnostic of intrauterine gestation. “Surrounding endometrium” or “double sac sign” .  Lack of an “interstitial line sign” or extension of endometrium to the gestational sac edge

18. Angular Pregnancy ( 4a and 4b) Transabdominal and transvaginal image of eccentrically located sac (arrow) in angular pregnancy. (4c) 3D image showing gestational sac (arrow) in the superolateral angle of the uterus.

19. Angular Pregnancy   A , Transvaginal transverse scan of the uterus shows an eccentric gestational sac (large arrow) implanted in the right lateral corner of the endometrial cavity (E). The pregnancy is intrauterine and has a broad interface with the endometrium (asterisks), which completely surrounds the gestational sac. The myometrium surrounds the outer border of the sac (small arrows).   B , Three‐dimensional coronal reconstruction of the uterus shows an early eccentrically located gestational sac (arrow) in the right lateral corner of the endometrial cavity. The pregnancy is intrauterine and has a broad interface with the endometrium (asterisks). 

20. Angular Pregnancy   (5 a) Eccentric gestation sac (arrow) located in the lateral angle of endometrial cavity, note the large broad-based connection with endometrium. (5b) Arrows point to the normal myometrium noted on the lateral angle.

21. Comparison between angular pregnancy and interstitial pregnancy    A , Transvaginal transverse scan of the uterus shows an angular pregnancy, which is an eccentric gestational sac (asterisk) implanted in the left lateral angle or corner of the endometrial cavity (E). The pregnancy is intrauterine and has a broad connection with the endometrium (arrowheads), which continues around the gestational sac. The myometrium surrounds the outer border of the sac (arrows).   B , Transvaginal transverse scan of the uterus shows the eccentrically located interstitial ectopic pregnancy (*), separate from the endometrial cavity (E). It is located in the interstitial portion of the fallopian tube as it passes through the cornual part of the uterus. Note that a thin band of myometrium (arrows) separates the interstitial ectopic sac from the endometrial cavity and surrounds the sac.

22. Management of Angular Pregnancy   Patients may have persistent pain and bleeding during pregnancy, and there are several reports in the literature of an increased risk of spontaneous abortion, uterine rupture (23.5% of cases), and abnormal implantation causing a morbidly adherent placenta.  The risks are probably exaggerated because cases of ectopic interstitial pregnancies are likely mixed in these reports. Nonetheless, more recent investigators believe that there still is increased risk associated with pregnancies located in the lateral corner of the endometrial cavity. Full-term delivery is likely as the gestational sac descends into the uterine cavity. In cases where the sac might not descend into the uterine cavity there may be tendency for rupture, hence it is also important to look for myometrial discontinuity and hemoperitoneum whenever angular pregnancy is suspected. Although a strategy of expectant management may be reasonable, continuous and careful monitoring of the mother and fetus is necessary.

23. Cornual Pregnancy The term “cornual pregnancy” is imprecise because it has been applied to 5 different types of pregnancies. Two of these are ectopic pregnancies, which by definition are pregnancies implanted outside the endometrial cavity, and 3 of these are intrauterine pregnancies. Many clinicians and radiologists use interstitial and cornual ectopic pregnancy interchangeably, while  o thers insist that cornual should only refer to a pregnancy in the cornu of an anomalous uterus.

24. Cornual Pregnancy Two of the 5 pregnancies that have been called cornual pregnancies are ectopic pregnancies: one being an interstitial ectopic pregnancy, which implants in the interstitial part of the fallopian tube, and the second being a pregnancy in the rudimentary horn of a unicornuate uterus. The other 3 are normal intrauterine pregnancies, which include a pregnancy in the cornu or horn of a bicornuate uterus, a pregnancy in the cornu or horn of a septate uterus, and a pregnancy referred to as an angular pregnancy, which is eccentrically located in the lateral angle of the endometrial cavity as it narrows toward the ostium of the fallopian tube

25. Cornual Pregnancy A I nterstitial ectopic pregnancy.  B Ectopic pregnancy in a non –communicating right rudimentary horn associated with a unicornuate uterus. C E ctopic pregnancy is implanted in a right communicating rudimentary horn. D This pregnancy is implanted in the right horn of a bicornuate uterus and is therefore an intrauterine pregnancy.  E This pregnancy is implanted in the right horn of a septate uterus and is therefore an intrauterine pregnancy.  F On the left side of the uterus, a pregnancy is implanted in the lateral angle of the endometrial cavity, most appropriately termed an “angular pregnancy,” which is an intrauterine pregnancy, not an ectopic pregnancy

26. Cornual Pregnancy The term “cornual pregnancy” has been used to describe all of these different types of pregnancies. Therefore, the term is potentially misleading, because it is confusing to sonologists and clinicians, and should not be used except for pregnancy in rudimentary horn ( either communicating or non communicating ) of unicornate uterus. ( Only B and C )

27. Cornual Pregnancy Cornual pregnancy in rudimentary horn. (7a) Transabdominal image of sagittal section of uterus. (7b) Gestational sac seen separate from the uterus surrounded by myometrium. (7c) A vascular pedicle joining the gestational sac to the unicornuate uterus, (7d) 3D rendering of uterus demonstrating right unicornuate uterus. (7e) 3D rendering of gestational sac in left rudimentary horn. (7f and 7g) 3D multiplanar imaging with VCI demonstrating unicornuate uterus with sac in left rudimentary horn.

28. Management of Cornual Pregnancy The differential diagnosis between cornual and other forms of ectopic pregnancy is important because of the different clinical implications and management strategies. Failure to diagnose a cornual pregnancy in rudimentary horn can lead to serious complications, while an diagnosis provides the option of safe and effective treatment. Although interstitial pregnancy can be treated by medical or conservative management, such management for cornual pregnancy in rudimentary horn is not advisable and should always be managed surgically

29. Take Home Message We are in the era of ART; Hence, we might face the dilemma of eccentrically located gestational sac with the need for accurate diagnosis as this is a precious pregnancy. Interstitial pregnancy is intracavitary ectopic pregnancy that must be terminated. Angular pregnancy is intrauterine pregnancy that can continue pregnancy with close monitoring. Cornual pregnancy should be only termed for pregnancy in rudimentary horn of unicornate uterus that should be surgically excised. Pregnancy in didelphys, bicornate and septate uterus should no longer termed cornual pregnancy to avoid false interpretation as they are normal intrauterine pregnancy.

30. Reference Differentiating pregnancies near the uterotubal junction (angular, cornual, and interstitial): a review and recommendations; 2020. The Term “Cornual Pregnancy” Should Be Abandoned; 2017. Diagnostic dilemmas of an eccentrically located gestation sac: role of 3D ultrasound; 2019.