Rivka Feig, MS4
The Article: Lee R, Dupuis C, Chen B, Smith A, Kim Y (2018) Diagnosing ectopic pregnancy in the emergency setting. Ultrasonography 37(1): 78-87
The Idea:
Ectopic pregnancy is an important diagnostic consideration for women presenting to the emergency department with abdominal or pelvic pain and/or vaginal bleeding. The diagnosis is based on a positive serum beta-hCG as well as ultrasound imaging. The early detection and treatment of an ectopic pregnancy improves outcomes. Ultrasound findings of ectopic pregnancy are variable and can be subtle, often making diagnosis challenging. This essay describes (and illustrates) the sonographic findings of ectopic pregnancy and reviews the differential diagnoses that can mimic an ectopic pregnancy on ultrasound.
Ectopic Pregnancy:
Ectopic pregnancy is the implantation of a fertilized egg outside of the endometrial cavity. 98% occur in the fallopian tubes, with the remainder found in the ovaries, cesarean section scars, cervix, and peritoneal cavity. Risk factors include pelvic inflammatory disease, previous ectopic pregnancy, and tubal surgery.
Imaging Technique:
Transabdominal evaluation with a low-frequency curvilinear probe offers a wide field of view of the pelvis, better visualization of the uterine fundus and can also visualize free fluid within the peritoneal cavity. Transvaginal examination with a high-frequency intracavitary probe provides superior near-field resolution which allows for more detailed evaluation of the endometrial cavity, ovaries , and other adnexal structures.
Visualization of an intra-uterine gestational sac along with normal adnexal structures can exclude ectopic pregnancy from the diagnostic differential.
If no IUP is identified in a patient with a beta hCG above the discriminatory zone, ectopic pregnancy cannot be excluded.
Ultrasound Findings of Ectopic Pregnancy:
Tubal ectopic pregnancy most commonly presents as an extraovarian heterogenous mass, which may demonstrate varying degrees of echogenicity. The second most common presentation is the tubal ring sign- an echogenic ring in the adnexa surrounding the ectopic pregnancy. Color doppler may show increased vascularity within the ring.
Other findings associated with ectopic pregnancy include the presence of intraperitoneal free fluid (69% specific and 63% sensitive for ectopic pregnancy in patients with a positive pregnancy test and an empty uterus), which can be either simple or complex.
A pseudo-gestational sac, which is a small amount of intra-uterine fluid, is present in 10% of patients with ectopic pregnancy, and can be misinterpreted as a true gestational sac. However, they can be differentiated with real-time imaging, which often demonstrates shifting of the fluid in a pseudo-sac, in contrast to the fixed position on a true gestational-sac.
Mimics of Ectopic Pregnancy:
A corpus luteum can look similar to an ectopic pregnancy on ultrasound. It is usually a round, cystic, thick-walled structure with varying internal echogenicity, which also shows increased circumferential vascularity on color doppler.
An incidental adnexal mass, such as a para-ovarian or dermoid cyst can also be mistaken for an ectopic pregnancy. Ovarian neoplasms can also mimic ectopic pregnancy. Visualization of bowel loops in the pelvis can occasionally be misinterpreted as ectopic pregnancy and vice versa.
Takeaway:
Ectopic pregnancy is a leading cause of pregnancy related mortality during the first trimester. Early detection can lead to timely intervention and decrease maternal morbidity and mortality, particularly with the increased use of medical management, which can avoid the need for surgery and prevent complications.
Ultrasound evaluation is a crucial element in the diagnosis of ectopic pregnancy, but requires careful and detailed scrutiny of the pelvic anatomy as the presentation of an ectopic pregnancy can vary and is occasionally mimicked by other findings.