(P102) Identifying Interstitial Ectopic Pregnancy on Transvaginal Point of Care Ultrasound

Chief Complaint : Abdominal pain

History of Present Illness : A female in her 30s with a past medical history of 2 vaginal deliveries and 1 dilation and curettage was referred to the emergency department due to concern for an ectopic pregnancy on ultrasound at her obstetrician’s office. She had seen an obstetrician to establish prenatal care following a positive home pregnancy test 4 days before presentation. She reported cramping suprapubic abdominal pain and mild vaginal bleeding for two days, with her LMP approximately 6 weeks ago.

Pertinent Physical Exam: Vital signs stable with heart rate 67 beats/min, blood pressure 121/76mmHg, respiratory rate 20 breaths/min, oxygen saturation 95%, and temperature 98.2°F. The patient was generally well-appearing with suprapubic tenderness and mild bleeding from a closed os.

Pertinent Laboratory Data: 𝛃-Hcg 4500, Hgb 11.3 (no baseline), Rh positive
Abdominal ultrasound showed no intraperitoneal free fluid and insufficient visualization of the uterus and adnexa. Transvaginal ultrasound (TVUS) demonstrated a thickened endometrial stripe (Image 1) and a gestational sac within the uterine myometrium (Image 2) containing a yolk sac and fetal pole with cardiac activity confirmed on M-mode. These findings raised concern for an interstitial pregnancy and gynecology was consulted.

Case Discussion: This case demonstrates the use of transvaginal ultrasound in the emergency department to identify a rare type of ectopic pregnancy with a higher risk of complications. Interstitial pregnancy (IP) is a type of tubal ectopic within the myometrium. They constitute 2-6.8% of ectopic pregnancies but with higher morbidity (2-2.5%) due to their proximity to the intramyometrial arcuate vasculature, and delayed diagnosis compared to other ectopic pregnancies.1 Ultrasound is the diagnostic standard, with diagnostic criteria defined as (1) an empty uterine cavity; (2) chorionic sac >1cm from lateral uterine border; and (3) myometrial layer < 5mm surrounding chorionic sac, with a specificity of 88-93% and sensitivity of 40%.2 On our POC TVUS, we first noted no gestational sac within the endometrial cavity, then identified a gestational sac surrounded by myometrium. IP must be differentiated from a viable angular pregnancy, with distinguishing criteria of (1) non-anomalous uterus, (2) embryonic implantation in the superior lateral angle of the uterus, (3) < 10mm myometrial thickness from gestational sac to outer border of uterus, and (4) gestational sac fully encompassed by circumferential endometrium.3, 4 If this determination cannot be made on ultrasound, MRI can be offered to clinically stable patients.

Treatment is either expectant, medical, or surgical, depending on patient preference and clinical status. Expectant or medical management with Methotrexate is first line for clinically stable patients.5 For unstable patients, including patients such as ours with stable vital signs but symptoms concerning for ectopic rupture, surgical options are cornuostomy or corneal resection.5 Based on our TVUS results, we consulted gynecology who took our patient to the OR for diagnostic laparoscopy, which found an unruptured right interstitial ectopic pregnancy. She underwent a right cornual wedge resection and salpingectomy and was discharged home in stable condition.

References and Acknowledgements (Optional): 1. Brincat M, Bryant-Smith A, Holland TK. The diagnosis and management of interstitial ectopic pregnancies: a review. Gynecol Surg. 2019 Feb 4; 16(2). doi:10.1186/s10397-018-1054-4
2. Timor-Tritsch IE, Monteagudo A, Matera C, Veit CR. Sonographic evolution of cornual pregnancies treated without surgery. Obstet Gynecol 1992 Jun 1; 79(6):1044–1049. PMID:1579304.
3. Durand YG, Capoccia-Brugger R, Vial Y, Balaya V. Diagnostic dilemma between angular and interstitial ectopic pregnancy: 3D ultrasound features. J Ultrasound. 2022 Apr 21; 25:989-994. doi:10.1007/s40477-022-00668-1
4. Bollig KF, Schust DJ. Refining angular pregnancy diagnosis in the first trimester: a case series of expectant management. Obstet Gynecol 2020 Jan; 135(1):175-184. doi:10.1097/AOG.0000000000003595.
5. Cassik P, Ofili-Yebovi D, Yazbek J, Lee C, Elson J, Jurkovic D. Factors influencing the success of conservative treatment of interstitial pregnancy. Ultrasound Obstet Gynecol. 2005 July 25; 26(3):279-282. doi:10.1002/uog.1961