Presentation
Patient presented for a dating scan after a positive urine beta hCG test at home.
Patient Data

Ovoid or flattened hypoechoic heterogeneous fluid collection that is eccentrically located in the region of the left superior uterine cornua, near the ostium of the left fallopian tube. On 3-D imaging, the fluid collection appears to be surrounded circumferentially by a thion layer of endometrium. No delineated yolk sac, fetal pole, or decidual reaction.
Subtle arcuate appearance of the uterine fundus on 3-D images.
Uterus is anteverted. The left ovary and right ovary are unremarkable in appearance.
Case Discussion
The eccentric location of the fluid collection near the uterine cornua makes interstitial ectopic pregnancy a consideration, although cornual pregnancy is also a possibility. Delineating these would require gauging the thickness of the endo-myometrium surrounding the gestational sac. This endometrial mantle thickness should not measure <5-8 mm, depending on the study 1. Although the measurement was not formally documented in this case, the appearance of the surrounding endo--myometrial mantle appears thin, but possibly borderline. If there is adequate thickness above this threshold, then an intrauterine, cornual pregnancy is the more likely diagnosis 2.
Incidental note of an arcuate morphology of the uterine fundus.